for Journals by Title or ISSN
for Articles by Keywords
help
  Subjects -> CHEMISTRY (Total: 846 journals)
    - ANALYTICAL CHEMISTRY (50 journals)
    - CHEMISTRY (597 journals)
    - CRYSTALLOGRAPHY (22 journals)
    - ELECTROCHEMISTRY (25 journals)
    - INORGANIC CHEMISTRY (41 journals)
    - ORGANIC CHEMISTRY (45 journals)
    - PHYSICAL CHEMISTRY (66 journals)

CHEMISTRY (597 journals)                  1 2 3 | Last

Showing 1 - 200 of 735 Journals sorted alphabetically
2D Materials     Hybrid Journal   (Followers: 7)
Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement     Hybrid Journal   (Followers: 26)
ACS Catalysis     Full-text available via subscription   (Followers: 31)
ACS Chemical Neuroscience     Full-text available via subscription   (Followers: 17)
ACS Combinatorial Science     Full-text available via subscription   (Followers: 23)
ACS Macro Letters     Full-text available via subscription   (Followers: 22)
ACS Medicinal Chemistry Letters     Full-text available via subscription   (Followers: 39)
ACS Nano     Full-text available via subscription   (Followers: 217)
ACS Photonics     Full-text available via subscription   (Followers: 10)
ACS Synthetic Biology     Full-text available via subscription   (Followers: 20)
Acta Chemica Iasi     Open Access   (Followers: 2)
Acta Chimica Sinica     Full-text available via subscription  
Acta Chimica Slovaca     Open Access   (Followers: 1)
Acta Chromatographica     Full-text available via subscription   (Followers: 9)
Acta Facultatis Medicae Naissensis     Open Access  
Acta Metallurgica Sinica (English Letters)     Hybrid Journal   (Followers: 5)
Acta Scientifica Naturalis     Open Access   (Followers: 2)
adhäsion KLEBEN & DICHTEN     Hybrid Journal   (Followers: 5)
Adhesion Adhesives & Sealants     Hybrid Journal   (Followers: 7)
Adsorption Science & Technology     Full-text available via subscription   (Followers: 5)
Advanced Functional Materials     Hybrid Journal   (Followers: 48)
Advanced Science Focus     Free   (Followers: 3)
Advances in Chemical Engineering and Science     Open Access   (Followers: 53)
Advances in Chemical Science     Open Access   (Followers: 12)
Advances in Chemistry     Open Access   (Followers: 12)
Advances in Colloid and Interface Science     Full-text available via subscription   (Followers: 18)
Advances in Drug Research     Full-text available via subscription   (Followers: 22)
Advances in Enzyme Research     Open Access   (Followers: 10)
Advances in Fluorine Science     Full-text available via subscription   (Followers: 8)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 14)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 8)
Advances in Materials Physics and Chemistry     Open Access   (Followers: 18)
Advances in Nanoparticles     Open Access   (Followers: 12)
Advances in Organometallic Chemistry     Full-text available via subscription   (Followers: 15)
Advances in Polymer Science     Hybrid Journal   (Followers: 40)
Advances in Protein Chemistry     Full-text available via subscription   (Followers: 18)
Advances in Protein Chemistry and Structural Biology     Full-text available via subscription   (Followers: 18)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 5)
Advances in Science and Technology     Full-text available via subscription   (Followers: 10)
African Journal of Bacteriology Research     Open Access  
African Journal of Chemical Education     Open Access   (Followers: 2)
African Journal of Pure and Applied Chemistry     Open Access   (Followers: 7)
Agrokémia és Talajtan     Full-text available via subscription   (Followers: 2)
Alkaloids: Chemical and Biological Perspectives     Full-text available via subscription   (Followers: 3)
AMB Express     Open Access   (Followers: 1)
Ambix     Hybrid Journal   (Followers: 3)
American Journal of Biochemistry and Biotechnology     Open Access   (Followers: 65)
American Journal of Biochemistry and Molecular Biology     Open Access   (Followers: 14)
American Journal of Chemistry     Open Access   (Followers: 25)
American Journal of Plant Physiology     Open Access   (Followers: 13)
American Mineralogist     Full-text available via subscription   (Followers: 12)
Analyst     Full-text available via subscription   (Followers: 38)
Angewandte Chemie     Hybrid Journal   (Followers: 153)
Angewandte Chemie International Edition     Hybrid Journal   (Followers: 203)
Annales UMCS, Chemia     Open Access   (Followers: 1)
Annals of Clinical Chemistry and Laboratory Medicine     Open Access   (Followers: 1)
Annual Reports in Computational Chemistry     Full-text available via subscription   (Followers: 3)
Annual Reports Section A (Inorganic Chemistry)     Full-text available via subscription   (Followers: 3)
Annual Reports Section B (Organic Chemistry)     Full-text available via subscription   (Followers: 7)
Annual Review of Chemical and Biomolecular Engineering     Full-text available via subscription   (Followers: 12)
Annual Review of Food Science and Technology     Full-text available via subscription   (Followers: 14)
Anti-Infective Agents     Hybrid Journal   (Followers: 3)
Antiviral Chemistry and Chemotherapy     Hybrid Journal  
Applied Organometallic Chemistry     Hybrid Journal   (Followers: 6)
Applied Spectroscopy     Full-text available via subscription   (Followers: 22)
Applied Surface Science     Hybrid Journal   (Followers: 26)
Arabian Journal of Chemistry     Open Access   (Followers: 6)
ARKIVOC     Open Access   (Followers: 2)
Asian Journal of Biochemistry     Open Access   (Followers: 1)
Atomization and Sprays     Full-text available via subscription   (Followers: 3)
Australian Journal of Chemistry     Hybrid Journal   (Followers: 7)
Autophagy     Hybrid Journal   (Followers: 2)
Avances en Quimica     Open Access   (Followers: 1)
Biochemical Pharmacology     Hybrid Journal   (Followers: 9)
Biochemistry     Full-text available via subscription   (Followers: 277)
Biochemistry Insights     Open Access   (Followers: 5)
Biochemistry Research International     Open Access   (Followers: 6)
BioChip Journal     Hybrid Journal  
Bioinorganic Chemistry and Applications     Open Access   (Followers: 9)
Bioinspired Materials     Open Access   (Followers: 3)
Biointerface Research in Applied Chemistry     Open Access   (Followers: 2)
Biointerphases     Open Access   (Followers: 1)
Biology, Medicine, & Natural Product Chemistry     Open Access  
Biomacromolecules     Full-text available via subscription   (Followers: 18)
Biomass Conversion and Biorefinery     Partially Free   (Followers: 10)
Biomedical Chromatography     Hybrid Journal   (Followers: 6)
Biomolecular NMR Assignments     Hybrid Journal   (Followers: 3)
BioNanoScience     Partially Free   (Followers: 4)
Bioorganic & Medicinal Chemistry     Hybrid Journal   (Followers: 107)
Bioorganic & Medicinal Chemistry Letters     Hybrid Journal   (Followers: 99)
Bioorganic Chemistry     Hybrid Journal   (Followers: 10)
Biopolymers     Hybrid Journal   (Followers: 18)
Biosensors     Open Access   (Followers: 2)
Biotechnic and Histochemistry     Hybrid Journal   (Followers: 1)
Bitácora Digital     Open Access  
Boletin de la Sociedad Chilena de Quimica     Open Access  
Bulletin of the Chemical Society of Ethiopia     Open Access   (Followers: 2)
Bulletin of the Chemical Society of Japan     Full-text available via subscription   (Followers: 24)
Bulletin of the Korean Chemical Society     Hybrid Journal   (Followers: 1)
C - Journal of Carbon Research     Open Access   (Followers: 2)
Canadian Association of Radiologists Journal     Full-text available via subscription   (Followers: 2)
Canadian Journal of Chemistry     Full-text available via subscription   (Followers: 10)
Canadian Mineralogist     Full-text available via subscription   (Followers: 3)
Carbohydrate Research     Hybrid Journal   (Followers: 26)
Carbon     Hybrid Journal   (Followers: 67)
Catalysis for Sustainable Energy     Open Access   (Followers: 6)
Catalysis Reviews: Science and Engineering     Hybrid Journal   (Followers: 8)
Catalysis Science and Technology     Free   (Followers: 6)
Catalysis Surveys from Asia     Hybrid Journal   (Followers: 3)
Catalysts     Open Access   (Followers: 7)
Cellulose     Hybrid Journal   (Followers: 7)
Cereal Chemistry     Full-text available via subscription   (Followers: 4)
ChemBioEng Reviews     Full-text available via subscription   (Followers: 1)
ChemCatChem     Hybrid Journal   (Followers: 8)
Chemical and Engineering News     Free   (Followers: 12)
Chemical Bulletin of Kazakh National University     Open Access  
Chemical Communications     Full-text available via subscription   (Followers: 69)
Chemical Engineering Research and Design     Hybrid Journal   (Followers: 23)
Chemical Research in Chinese Universities     Hybrid Journal   (Followers: 3)
Chemical Research in Toxicology     Full-text available via subscription   (Followers: 19)
Chemical Reviews     Full-text available via subscription   (Followers: 165)
Chemical Science     Open Access   (Followers: 21)
Chemical Technology     Open Access   (Followers: 15)
Chemical Vapor Deposition     Hybrid Journal   (Followers: 4)
Chemical Week     Full-text available via subscription   (Followers: 7)
Chemie in Unserer Zeit     Hybrid Journal   (Followers: 55)
Chemie-Ingenieur-Technik (Cit)     Hybrid Journal   (Followers: 25)
ChemInform     Hybrid Journal   (Followers: 7)
Chemistry & Biodiversity     Hybrid Journal   (Followers: 6)
Chemistry & Biology     Full-text available via subscription   (Followers: 30)
Chemistry & Industry     Hybrid Journal   (Followers: 5)
Chemistry - A European Journal     Hybrid Journal   (Followers: 136)
Chemistry - An Asian Journal     Hybrid Journal   (Followers: 15)
Chemistry and Materials Research     Open Access   (Followers: 17)
Chemistry Central Journal     Open Access   (Followers: 4)
Chemistry Education Research and Practice     Free   (Followers: 5)
Chemistry in Education     Open Access   (Followers: 9)
Chemistry International     Hybrid Journal   (Followers: 2)
Chemistry Letters     Full-text available via subscription   (Followers: 43)
Chemistry of Materials     Full-text available via subscription   (Followers: 189)
Chemistry of Natural Compounds     Hybrid Journal   (Followers: 9)
Chemistry-Didactics-Ecology-Metrology     Open Access  
ChemistryOpen     Open Access   (Followers: 2)
Chemkon - Chemie Konkret, Forum Fuer Unterricht Und Didaktik     Hybrid Journal  
Chemoecology     Hybrid Journal   (Followers: 2)
Chemometrics and Intelligent Laboratory Systems     Hybrid Journal   (Followers: 15)
Chemosensors     Open Access  
ChemPhysChem     Hybrid Journal   (Followers: 8)
ChemPlusChem     Hybrid Journal   (Followers: 2)
ChemTexts     Hybrid Journal  
CHIMIA International Journal for Chemistry     Full-text available via subscription   (Followers: 2)
Chinese Journal of Chemistry     Hybrid Journal   (Followers: 6)
Chinese Journal of Polymer Science     Hybrid Journal   (Followers: 10)
Chromatographia     Hybrid Journal   (Followers: 23)
Chromatography Research International     Open Access   (Followers: 7)
Clay Minerals     Full-text available via subscription   (Followers: 9)
Cogent Chemistry     Open Access  
Colloid and Interface Science Communications     Open Access  
Colloid and Polymer Science     Hybrid Journal   (Followers: 10)
Colloids and Surfaces B: Biointerfaces     Hybrid Journal   (Followers: 8)
Combinatorial Chemistry & High Throughput Screening     Hybrid Journal   (Followers: 3)
Combustion Science and Technology     Hybrid Journal   (Followers: 18)
Comments on Inorganic Chemistry: A Journal of Critical Discussion of the Current Literature     Hybrid Journal   (Followers: 2)
Composite Interfaces     Hybrid Journal   (Followers: 6)
Comprehensive Chemical Kinetics     Full-text available via subscription   (Followers: 2)
Comptes Rendus Chimie     Full-text available via subscription  
Comptes Rendus Physique     Full-text available via subscription   (Followers: 1)
Computational and Theoretical Chemistry     Hybrid Journal   (Followers: 9)
Computational Biology and Chemistry     Hybrid Journal   (Followers: 12)
Computational Chemistry     Open Access   (Followers: 2)
Computers & Chemical Engineering     Hybrid Journal   (Followers: 9)
Coordination Chemistry Reviews     Full-text available via subscription   (Followers: 2)
Copernican Letters     Open Access  
Critical Reviews in Biochemistry and Molecular Biology     Hybrid Journal   (Followers: 5)
Crystal Structure Theory and Applications     Open Access   (Followers: 3)
CrystEngComm     Full-text available via subscription   (Followers: 10)
Current Catalysis     Hybrid Journal   (Followers: 2)
Current Metabolomics     Hybrid Journal   (Followers: 4)
Current Opinion in Colloid & Interface Science     Hybrid Journal   (Followers: 9)
Current Research in Chemistry     Open Access   (Followers: 8)
Current Science     Open Access   (Followers: 48)
Dalton Transactions     Full-text available via subscription   (Followers: 18)
Detection     Open Access   (Followers: 2)
Developments in Geochemistry     Full-text available via subscription   (Followers: 2)
Diamond and Related Materials     Hybrid Journal   (Followers: 11)
Dislocations in Solids     Full-text available via subscription  
Doklady Chemistry     Hybrid Journal  
Drying Technology: An International Journal     Hybrid Journal   (Followers: 3)
Eclética Química     Open Access   (Followers: 1)
Ecological Chemistry and Engineering S     Open Access   (Followers: 4)
Ecotoxicology and Environmental Contamination     Open Access  
Educación Química     Open Access   (Followers: 1)
Education for Chemical Engineers     Hybrid Journal   (Followers: 5)
EJNMMI Radiopharmacy and Chemistry     Open Access  
Elements     Full-text available via subscription   (Followers: 2)
Environmental Chemistry     Hybrid Journal   (Followers: 8)
Environmental Chemistry Letters     Hybrid Journal   (Followers: 4)
Environmental Science & Technology Letters     Full-text available via subscription   (Followers: 5)
Environmental Science : Nano     Partially Free   (Followers: 1)
Environmental Toxicology & Chemistry     Hybrid Journal   (Followers: 19)

        1 2 3 | Last

Journal Cover Chemistry - A European Journal
  [SJR: 2.323]   [H-I: 188]   [136 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0947-6539 - ISSN (Online) 1521-3765
   Published by John Wiley and Sons Homepage  [1583 journals]
  • Metal-Free Arene and Heteroarene Borylation Catalyzed by Strongly
           Electrophilic Bis-boranes
    • Authors: Yun-Lin Liu; Gerald Kehr, Constantin G. Daniliuc, Gerhard Erker
      Abstract: The geminal chelate bis-borylalkanes 4 and 5 featuring strongly electrophilic B(C6F5)2 and B(C6F5) groups, respectively, serve as efficient catalysts for the borylation of arenes and heteroarenes. The borylation reactions proceed under mild conditions with liberation of dihydrogen.Geminal pentafluorophenyl-containing bis-borylalkanes efficiently catalyze the borylation reaction of a variety of arenes and heteroarenes at RT with liberation of dihydrogen.
      PubDate: 2017-05-26T04:45:37.109766-05:
      DOI: 10.1002/chem.201701771
       
  • Tellurite-Squarate Driven Assembly of a New Family of Nanoscale Clusters
           based on (Mo2O2S2)2+
    • Authors: Lee Cronin; Jamie Purcell, Haralampos Miras, De-Liang Long, Panagiota Markopoulou
      Abstract: We report the preparation and characterization of a new family of four polyoxothiometalate (POTM) clusters, with varying size and complexity, based upon the dimeric [Mo2O2S2(H2O)6]2+ with the general formula (NMe4)aKb[(Mo2O2S2)c(TeO4)d(C4O4)e(OH)f] where a,b,c,d,e,f = {1,7,14,2,4,10} = 1, {Mo28Te2}; {2,26,36,4,10,48} = 2, {Mo72Te12}; {0,11,15,3,3,21} = 3, {Mo30Te3}; {2,6,12,2,4,16} = 4, {Mo24Te2}. The incorporation of tellurite anions allowed the fine tuning of the templation and bridging of the available building blocks leading to new topologies of increased complexity. The structural diversity of this family of compound, ranges from the highly symmetrical cross-shaped {Mo24Te2} to the stacked ring structure of {Mo72Te12} which is the largest chalcogen-containing POTM cluster reported so far. Also a detailed experimental analysis revealed that the pH isolation window extends form acidic to basic values. ESI-MS analyses not only confirmed the stability of this family in solution but also revealed the stability of the observed virtual building blocks.
      PubDate: 2017-05-26T04:25:55.975851-05:
      DOI: 10.1002/chem.201701920
       
  • Multivalency to inhibit and discriminate hexosaminidases
    • Authors: Yves Bleriot; dimitri alvarez-dorta, dustin t king, thibaut legigan, daisuke ide, isao adachi, david deniaud, jerome desire, atsushi kato, david vocadlo, sebastien gouin
      Abstract: A set of multivalent polyhydroxylated acetamidoazepanes based on ethylene glycol, glucoside or cyclodextrin scaffolds was prepared. The compounds were assessed against plant, mammalian and therapeutically relevant hexosaminidases. Multimerization was shown to improve the inhibitory potency with synergy, and to fine tune the selectivity profile between related hexosaminidases.
      PubDate: 2017-05-26T04:25:52.818822-05:
      DOI: 10.1002/chem.201701756
       
  • Frontispiece: Twisted Amides: From Obscurity to Broadly Useful
           Transition-Metal-Catalyzed Reactions by N−C Amide Bond Activation
    • Authors: Chengwei Liu; Michal Szostak
      Abstract: Twisted amides: The use of amide bond twist (distortion) has advanced to the general organic chemistry mainstream enabling a host of highly attractive N−C amide bond cross-coupling reactions of broad synthetic relevance. In their Minireview, M. Szostak and C. Liu on page 7157 ff. discuss recent progress in this area and provide a detailed overview of the prominent role of amide bond twist as a driving force in the development of transition-metal-catalyzed cross-coupling reactions by N−C amide bond activation.
      PubDate: 2017-05-26T04:24:55.120938-05:
      DOI: 10.1002/chem.201783061
       
  • Frontispiece: Molecular Assemblies of Metal Complexes via Base-Pairing of
           Nucleic Acids in the Crystalline State
    • Authors: Manabu Nakaya; Ryo Ohtani, Kunihisa Sugimoto, Masaaki Nakamura, Leonard F. Lindoy, Shinya Hayami
      Abstract: The assembly arrangement of nucleobase-appended terpyridine cobalt(II) complexes, [Co(A-C6-terpy)2](BF4)2 and [Co(T-C6-terpy)2](BF4)2 is investigated. In addition a single crystal structure of heteroleptic terpyridine cobalt(II) complexes, [Co(A-C6-terpy)(T-C6-terpy)](BF4)2 has been obtained successfully for the first time. The complex exhibited dimer ring structure through the base pairings. This result shows that use of base pairings is useful for construction of supramolecular structures. For more details, see the Full Paper by S. Hayami et al. on page 7232 ff.
      PubDate: 2017-05-26T04:24:50.674596-05:
      DOI: 10.1002/chem.201783063
       
  • Frontispiece: Double Sequential Encrypted Targeting Sequence: A New
           Concept for Bone Cancer Treatment
    • Authors: Gonzalo Villaverde; Valentina Nairi, Alejandro Baeza, María Vallet-Regí
      Abstract: The efficacy of conventional chemotherapy is severely compromised by the associated systemic toxicity caused by lack of selectivity. In this work, we propose a novel double sequential encrypted targeting system that contains an active primary targeting group able to recognize the target tissue (bone) and an encrypted or hidden secondary targeting moiety able to recognize malignant cells that populate the diseased tissue. Once the system reaches the tumoral place, the presence of a characteristic enzyme naturally overproduced by malignant cells (cathepsin K) provokes the activation of the cellular targeting moiety inducing the uptake within the diseased cells. For more information, see the Communication by Vallet-Regí et al. on page 7174 ff.
      PubDate: 2017-05-26T04:24:48.867131-05:
      DOI: 10.1002/chem.201783062
       
  • d-Cysteine Ligands Control Metal Geometries within De Novo Designed
           Three-Stranded Coiled Coils
    • Authors: Leela Ruckthong; Anna F. A. Peacock, Cherilyn E. Pascoe, Lars Hemmingsen, Jeanne A. Stuckey, Vincent L. Pecoraro
      Abstract: Although metal ion binding to naturally occurring l-amino acid proteins is well documented, understanding the impact of the opposite chirality (d-)amino acids on the structure and stereochemistry of metals is in its infancy. We examine the effect of a d-configuration cysteine within a designed l-amino acid three-stranded coiled coil in order to enforce a precise coordination number on a metal center. The d chirality does not alter the native fold, but the side-chain re-orientation modifies the sterics of the metal binding pocket. l-Cys side chains within the coiled-coil structure have previously been shown to rotate substantially from their preferred positions in the apo structure to create a binding site for a tetra-coordinate metal ion. However, here we show by X-ray crystallography that d-Cys side chains are preorganized within a suitable geometry to bind such a ligand. This is confirmed by comparison of the structure of ZnIICl(CSL16DC)32− to the published structure of ZnII(H2O)(GRAND-CSL12AL16LC)3−. Moreover, spectroscopic analysis indicates that the CdII geometry observed by using l-Cys ligands (a mixture of three- and four-coordinate CdII) is altered to a single four-coordinate species when d-Cys is present. This work opens a new avenue for the control of the metal site environment in man-made proteins, by simply altering the binding ligand with its mirror-imaged d configuration. Thus, the use of non-coded amino acids in the coordination sphere of a metal promises to be a powerful tool for controlling the properties of future metalloproteins.Cysteine in the mirror: The effect of changing the configuration of an amino acid from l to d within metal-binding peptide sequences is investigated. By substituting l-Cys with d-Cys residues a new binding situation for metal ions was created (see figure). This observation opens new possibilities for protein designers to control the properties of future metalloproteins.
      PubDate: 2017-05-26T02:11:19.705385-05:
      DOI: 10.1002/chem.201700660
       
  • Liquid/Liquid Interfacial Synthesis of a Click Nanosheet
    • Authors: Amalia Rapakousiou; Ryota Sakamoto, Ryo Shiotsuki, Ryota Matsuoka, Ukyo Nakajima, Tigmansu Pal, Rintaro Shimada, Amran Hossain, Hiroyasu Masunaga, Satoshi Horike, Yasutaka Kitagawa, Sono Sasaki, Kenichi Kato, Takeaki Ozawa, Didier Astruc, Hiroshi Nishihara
      Abstract: A liquid/liquid interfacial synthesis is employed, for the first time, to synthesize a covalent two-dimensional polymer nanosheet. Copper-catalyzed azide–alkyne cycloaddition (CuAAC) between a three-way terminal alkyne and azide at a water/dichloromethane interface generates a 1,2,3-triazole-linked nanosheet. The resultant nanosheet, with a flat and smooth texture, has a maximum domain size of 20 μm and minimum thickness of 5.3 nm. The starting monomers in the organic phase and the copper catalyst in the aqueous phase can only meet at the liquid/liquid interface as a two-dimensional reaction space; this allows them to form the two-dimensional polymer. The robust triazole linkage generated by irreversible covalent-bond formation allows the nanosheet to resist hydrolysis under both acidic and alkaline conditions, and to endure pyrolysis up to more than 300 °C. The coordination ability of the triazolyl group enables the nanosheet to act as a reservoir for metal ions, with an affinity order of Pd2+>Au3+>Cu2+.Between the layers: A liquid/liquid interfacial synthesis is employed to synthesize a covalent two-dimensional nanosheet. Copper-catalyzed azide–alkyne cycloaddition of a triangular terminal alkyne and azide at the interface generates a triazole-linked nanosheet (see figure). The irreversible, robust, and metal-coordinating triazole linkage allows the nanosheet to resist hydrolysis under acidic and alkaline conditions, withstand heat to>300 °C, and to take up metal ions selectively.
      PubDate: 2017-05-26T02:11:12.61473-05:0
      DOI: 10.1002/chem.201700201
       
  • Mechanistic Aspects in the Formation, Growth and Surface Functionalization
           of Metal Oxide Nanoparticles in Organic Solvents
    • Authors: Rupali Deshmukh; Markus Niederberger
      Abstract: The synthesis of metal oxide nanoparticles in organic solvents, so-called nonaqueous (or nonhydrolytic) processes represent powerful alternatives to aqueous approaches and have become an independent research field. 10 Years ago, when we published our first review on organic reaction pathways in nonaqueous sol–gel approaches, the number of examples was relatively limited. Nowadays, it is almost impossible to provide an exhaustive overview. Here we review the development of the last few years, without neglecting pioneering examples, which help to follow the historical development. The importance of a profound understanding of mechanistic aspects of nanoparticle crystallization and formation mechanisms can't be overestimated, when it comes to the design of rational synthesis concepts under minimization of trial-and-error experiments. The main reason for the progress in mechanistic understanding lies in the availability of characterization tools that make it possible to monitor chemical reactions from the dissolution of the precursor to the nucleation and growth of the nanoparticles, by ex situ methods involving sampling after different reaction times, but more and more also by in situ studies. After a short introduction to experimental aspects of nonaqueous sol–gel routes to metal oxide nanoparticles, we provide an overview of the main and basic organic reaction pathways in these approaches. Afterwards, we summarize the main characterization methods to study formation mechanisms, and then we discuss in great depth the chemical formation mechanisms of many different types of metal oxide nanoparticles. The review concludes with a paragraph on selected crystallization mechanisms reported for nonaqueous systems and a few illustrative examples of nonaqueous sol–gel concepts applied to surface chemistry.Chemical formation and crystallization mechanisms play an outstanding role in the development of rational synthesis routes to inorganic nanoparticles. In this review, the mechanistic aspects of metal oxide nanoparticle formation in organic solvents are discussed with a focus on the organic reaction pathways.
      PubDate: 2017-05-26T02:11:09.593531-05:
      DOI: 10.1002/chem.201605957
       
  • Heterotetracenes: Flexible Synthesis and in Silico Assessment of the
           Hole-Transport Properties
    • Authors: Yifan Li; Ganna Gryn'ova, Felipe Saenz, Xavier Jeanbourquin, Kevin Sivula, Clémence Corminboeuf, Jérôme Waser
      Abstract: Thienoacenes and furoacenes are among the most frequent molecular units found in organic materials. The efficient synthesis of morphologically different heteroacenes and the rapid determination of their solid-state and electronic properties are still challenging tasks, which slow down progress in the development of new materials. Here, we report a flexible and efficient synthesis of unprecedented heterotetracenes based on a platinum- and gold-catalyzed cyclization–alkynylation domino process using EthynylBenziodoXole (EBX) hypervalent iodine reagents in the key step. The proof-of-principle in silico estimation of the synthesized tetracenes’ charge transport properties reveals their strong dependence on both the position and nature of the heteroatoms in the ring system. A broad range of mobility is predicted, with some compounds displaying performance potentially comparable to that of state-of-the-art electronic organic materials.Acenes, acenes everywhere: Thienoacenes and furoacenes are among the most frequent molecular units found in organic materials. Here, we report a flexible and efficient synthesis of heterotetracenes based on a platinum- and gold-catalyzed cyclization–alkynylation domino process using ethynylbenziodoxole (EBX) hypervalent iodine reagents in the key step, as well the in silico estimation of the synthesized tetracenes’ charge mobility.
      PubDate: 2017-05-26T02:10:56.467149-05:
      DOI: 10.1002/chem.201701139
       
  • Alkynyl N-Nosylhydrazones: Easy Decomposition to Alknynl Diazomethanes and
           Application for Allene Synthesis
    • Authors: Xihe Bi; Yang Yang, Zhaohong Liu, Alessio Porta, Giuseppe Zanoni
      Abstract: The dissociation of N-tosylhydrazones is a safe and convenient method for the generation of donor carbenes. However, alkynyl carbenes cannot be isolated by this route because they readily undergo intramolecular cyclization to pyrazoles as soon as formed from alkynyl N-tosylhydrazones. Herein we report the use of alkynyl N-nosylhydrazones for the in situ generation of alkynyl carbenes and their coupling reaction with boronic acids under metal-free conditions, giving rise to a wide array of di- and trisubstituted allenes. Preliminary mechanistic investigations demonstrated that γ-protodeboration of propargyl boric acid was responsible for the initial allene formation. This methodology based on the nosyl group allows for novel transformations that involve an alkynylcarbene transient species.
      PubDate: 2017-05-26T00:20:35.278322-05:
      DOI: 10.1002/chem.201701462
       
  • Organic CO-prodrugs: Structure CO-release rate relationship Studies
    • Authors: Binghe Wang; Zhixiang Pan, Xingyue Ji, Vayou Chittavong, Wei Li, Kaili Ji, Mengyuan Zhu, Jun Zhang
      Abstract: Carbon monoxide (CO) is an endogenously produced gasotransmitter in mammals, and may have signaling roles in bacteria as well. It has many recognized therapeutic effects. A significant challenge in this field is the development of pharmaceutically acceptable forms of CO delivery with controllable and tunable release rates. Herein, we describe the structure-release rate studies of the first class of organic CO-prodrugs that release CO in aqueous solution at neutral pH.
      PubDate: 2017-05-25T13:20:25.183385-05:
      DOI: 10.1002/chem.201700936
       
  • Inosine can increase DNA's susceptibility to photo-oxidation by a Ru(II)
           complex due to structural change in the minor groove
    • Authors: John M. Kelly; Paraic Keane, James Hall, Fergus Poynton, Bjorn Poulsen, Sarah Gurung, Ian Clark, Igor Sazanovich, Michael Towrie, Thorfinnur Gunnlaugsson, Susan Quinn, Christine Cardin
      Abstract: Key to the development of DNA-targeting phototherapeutic drugs is determining the interplay between the photoactivity of the drug and its binding preference for a target sequence. For the photo-oxidising lambda-[Ru(TAP)2(dppz)]2+ (Ʌ-1) complex bound to either d{T1C2G3G4C5G6C7C8G9A10}2 (G9) or d{TCGGCGCCIA}2 (I9), the X-ray crystal structures shows the dppz intercalated at the terminal T1C2;G9A10 step or T1C2;I9A10 step. Thus substitution of the G9 nucleobase by inosine does not affect intercalation in the solid state although with I9 the dppz is more deeply inserted. In solution it is found that the extent of guanine photo-oxidation, and the rate of back electron transfer, as determined by ps and ns time-resolved infrared and transient visible absorption spectroscopy, is enhanced in I9, despite it containing the less oxidisable inosine. This is attributed to the nature of the binding in the minor groove due to the absence of an NH2 group. Similar behaviour and the same binding site in the crystal.are found for d{TTGGCGCCAA}2 (A9), In solution we propose that intercalation occurs at the C2G3;C8I9 or T2G3;C8A9 steps, respectively, with G3 the likely target for photo-oxidation. This demonstrates how changes in the minor groove (in this case removal of an NH2 group) can facilitate binding of Ru(II)dppz complexes and hence influence any sensitised reactions occurring at these sites. No similar enhancement of photooxidation on binding to I9 is found for the delta enantiomer.
      PubDate: 2017-05-25T05:20:33.702028-05:
      DOI: 10.1002/chem.201701447
       
  • An Efficient Pd-Catalyzed Regio- and Stereoselective Carboxylation of
           Allylic Alcohols with Formic Acid
    • Authors: Yao Fu; Rui Shang, Ming-Chen Fu, Wan-Min Cheng
      Abstract: Formic acid is efficiently used as a C1 source to directly carboxylate allylic alcohols in the presence of a low loading of palladium catalyst and acetic anhydride as additive to afford β,γ-unsaturated carboxylic acids with excellent chemo-, regio-, and stereoselectivity. The reaction proceeds through a carbonylation process with in situ-generated carbon monoxide (CO) under mild conditions, avoiding the use of high-pressure gaseous CO. A bisphosphine ligand that has a large bite angle (4,5-bis(diphenylphosphino)-9,9-dimethylxanthene) was found to be uniquely effective for this transformation. The regio- and stereoconvergence of this reaction is ascribed to the thermodynamically favored isomerization of the allylic electrophile in the presence of the palladium catalyst.
      PubDate: 2017-05-25T05:20:29.731098-05:
      DOI: 10.1002/chem.201701971
       
  • Covalently modified graphenes in catalysis, electrocatalysis and
           photoresponsive materials.
    • Authors: Sergio Navalon; Jose Raul Herance, Mercedes Alvaro, Hermenegildo García
      Abstract: Ideal graphene is a one-atom thick single layer of carbon atoms having sp2 hybridation in hexagonal arrangement. Due to their large surface area and good dispersability in common solvents, graphenes are suitable platforms to anchor covalently units. The appended unit can introduce additional functionality to graphene. Although the field of covalently modified graphene is still starting compared to the development of other carbon nanoforms, there is alrady many examples describing the use of modified graphenes as recoverable photo-, electro- and catalysts as well as in non-linear optics and to improve mechanical resistance and solubility of graphenes. In this review, the state of the art of covalently modified graphenes for these applications is reviewed. After some general sections describing properties and characterization techniques of graphenes relevant to their use as supports and those general reaction and starting substrates to obtain the modified graphene conjugates, the main body of the review is describes the preparation and properties of covalently modified graphene depending on their use as catalyst, photocatalyst, photoresponsive material, non-linear optics, electrocatalyst and other uses. The last section of the review summarizes the main achievements of the field and what should be according to our view the future developments.Introduction
      PubDate: 2017-05-25T05:20:28.155698-05:
      DOI: 10.1002/chem.201701028
       
  • Synthesis of a Single-Crystalline Macroporous Layered Silicate from
           Macroporous UTL-Type Zeolite and its Accelerated Intercalation
    • Authors: Yusuke Asakura; Naoki Kawaura, Yoshiyuki Kuroda, Masakazu Koike, Hiroaki Wada, Atsushi Shimojima, Kazuyuki Kuroda
      Abstract: A single-crystalline macroporous layered silicate was obtained for the first time. Firstly, UTL-type zeolite with macropores was prepared hydrothermally under the presence of acetylene black as a macropore template and the subsequent calcination to remove the template. Double four-membered ring (d4r) units in the UTL framework were selectively dissolved to yield a layered silicate with macropores. Intercalation of tetrabutylammonium ions into the macroporous layered silicate is accelerated if compared with that into the same silicate without macropores, indicating the effectiveness of macropores due to easy diffusion. The layered silicate with macropores was converted into PCR-type zeolite with macropores, a hierarchically micro- and macro-porous material, through interlayer condensation.
      PubDate: 2017-05-25T04:20:55.515092-05:
      DOI: 10.1002/chem.201701504
       
  • A New Polyoxometalate (POM)-Based Composite  Fabrication through
           POM-Assisted Polymerization of Dopamine and Properties as Anode Materials
           for High-Performance Lithium Ion Battery
    • Authors: Yan-Hong Ding; Jun Peng, Shifa-Ullah Khan, Yue Yuan
      Abstract: Abstract: Organic substrates are indispensable to fabricate multi-functional polyoxometalate (POM)-based composites for various application fields. A new Molybdovanadophosphoric heteropolyacid (PMo10V2)-based polydopamine (PDA) composite (PMo10V2/PDA) has been firstly synthesized through a facile in-situ polymerization method under hydrothermal conditions without adding extra buffer solution. The obtained PMo10V2/PDA composite shows homogeneous microsphere morphology. By utilizing the adhesive ability of PDA, the composite can be used as an anode material without additional binder for rechargeable lithium ion batteries. Excellent electrochemical performances are obtained with a high stable specific capacity of 915.3 mA h g-1 at a current density of 100 mA g-1, remarkable rate capability, and good stable cyclability (~93% capacity remained after 300 cycles at a high current density of 1000 mA g-1).
      PubDate: 2017-05-24T23:20:27.192335-05:
      DOI: 10.1002/chem.201700773
       
  • Tunable wettability of electrospun polyurethane/silica composite membranes
           for effective separation of water-in-oil and oil-in-water emulsions
    • Authors: Libin Liu; Wenyuan Fang, Gailan Guo
      Abstract: Polymer-dominated membranes with switchable wettability are highly desired due to their on-demand applications for oil/water separation. Herein, we report a low-cost methodology to fabricate membranes consisting of hyperbranched polyurethane (HBPU) and fluorine-modified silica (F-SiO2) with tunable wettability by electrospinning. The HBPU/F-SiO2 composite membranes can be transformed from superhydrophobicity to superhydrophilicity via plasma treatment, which exhibit different wettability for effective separation of surfactant-stabilized water-in-oil and oil-in-water emulsions.
      PubDate: 2017-05-24T21:20:29.52569-05:0
      DOI: 10.1002/chem.201701409
       
  • Self-assembly of perylenediimide-single strand DNA conjugates: Employing
           hydrophobic interactions and DNA base pairing to create a diverse
           structural space
    • Authors: Frederick Lewis; Ashutosh Kumar Mishra, Haim Weissman, Elisha Krieg, Kevin A. Voltaw, Martin McCullagh, Boris Rybtchiinski
      Abstract: The self-assembly behavior of DNA conjugates possessing a perylenediimide (PDI) head group and a single N-oligonucleotide tail has been investigated using a combination of optical spectroscopy and cryogenic transmission electron microscopy (cryo-TEM) imaging. In order to obtain insight into the interplay between DNA base pairing and PDI hydrophobic interactions we employed systematic variation in the length and composition of the oligo tails. Conjugates with short (TA)n or (CG)n oligo tails (n ≤ 3) form fibers (helical or nonhelical) constructed from -stacked PDI head groups with pendent oligo tails at room temperature in aqueous solution. Conjugates with longer (TA)n oligo tails also form stacks of PDI head groups in solution, which are further stabilized by base pairing between their oligo tails, leading to fiber bundling and formation of bilayers. The longer (CG)n conjugates (n  3) form PDI end-capped duplexes, which further assemble into PDI-stacked arrays of duplexes leading to large scale ordered assemblies. Cryo-TEM imaging reveals that (CG)3 gives rise to both fibers and large assemblies, while (CG)5 assembles preferentially into large ordered structures. Overall, we show that the PDI-N-oligonucleotide conjugate motif can assemble via hydrophobic -stacking and/or oligo base pairing resulting in a diverse structural space. Our findings provide guidelines for the design of simple and complex structures from molecules containing DNA strands and hydrophobic moieties.
      PubDate: 2017-05-24T15:20:25.268681-05:
      DOI: 10.1002/chem.201700752
       
  • Photoelectrochemical Catalysis toward Selective Anaerobic Oxidation of
           Alcohols
    • Authors: Ruikang Zhang; Mingfei Shao, Zhenhua Li, Fanyu Ning, Min Wei, David G. Evans, Xue Duan
      Abstract: Selective oxidation of alcohols to aldehydes plays an important role in perfumery, pharmaceuticals, and agrochemicals industry. Different from traditional catalysis or photocatalytic process, here we report an effective photoelectrochemical (PEC) approach for selective anaerobic oxidation of alcohols accompanied with H2 production by means of solar energy. By using TiO2 nanowires modified with graphitic carbon layer as photoanode, benzyl alcohol (BA) has been oxidized to benzaldehyde with high efficiency and selectivity (>99 %) in aqueous media at room temperature, superior to individual electrocatalytic or photocatalytic processes. Moreover, this PEC synthesis method can be effectively extended to the oxidation of several other aryl alcohols to their corresponding aldehydes under mild conditions. The electron spin resonance (ESR) results indicate the formation of intermediate active oxygen (O2.−) on the photoanode, which further reacts with alcohols to produce final aldehyde compounds.A green organic synthesis route, based on the photoelectrochemical water-splitting alcohol oxidation reaction coupling, has been developed.
      PubDate: 2017-05-24T09:05:26.033413-05:
      DOI: 10.1002/chem.201701107
       
  • Markovnikov versus anti-Markovnikov hydrophosphination: Divergent
           reactivity using an iron(II) β-diketiminate pre-catalyst
    • Authors: Andrew King; Kimberley Gallagher, Mary F. Mahon, Ruth L. Webster
      Abstract: The ability to tune between different regioselectivities using a common pre-catalyst is an unusual yet highly desirable process. Herein, we report the use of an iron(II) pre-catalyst that can be used to synthesize vinyl phosphines in a Markovnikov selective manner in benzene, whereas a simple change to dichloromethane as the reaction solvent leads to the Z-selective anti-Markovnikov functionalization. Preliminary mechanistic that studies suggest Markovnikov selectivity is a radical mediated process whereas the anti-Markovnikov selectivity is not radical in nature, and is due to a change in oxidation state, are reported.
      PubDate: 2017-05-24T08:35:33.8256-05:00
      DOI: 10.1002/chem.201702374
       
  • A Homochiral {CoΙΙ16CoΙΙΙ4} Supertetrahedral T4 Cluster from a
           Racemic Ligand with Ferromagnetic Behavior and High Photocatalytic
           Activity
    • Authors: Wei Du; Yue-Ling Bai, Xiuping Yin, Jianhui Fang, Shourong Zhu, Jun Tao
      Abstract: A homochiral mixed-valence cobalt cluster [CoΙΙ16CoΙΙΙ4(μ6-O)4(μ3-OH)12(S-bme)12(OAc)6]Cl6⋅5 CH3OH⋅18 H2O (1, Hbme=1H-(benzimidazol-2-yl)ethanol) was synthesized from a racemic ligand and three cobalt salts of CoCl2⋅6 H2O, Co(Ac)2⋅4 H2O and Co(NO3)2⋅6 H2O in a DMF/MeOH mixed solvent. The enantioselective coordination occurs when a large excess of cobalt ions added in the solution and only the S-configuration of the racemic ligand involved in crystallization. The CD spectra of three crystal samples show identical Cotton signals, indicating the repeatability and the enantiomeric purity of the single crystals. This compound presents a beautiful two-shell Matryoshka-type supertetrahedral T4 cluster constructed by an inner CoΙΙΙ4O4 cubane and four exterior CoΙΙ4O4 cubanes bridged by μ6-O2− and μ3-OH− ions. This highest nuclear chiral cobalt cluster is the first example of enantiopure cobalt cluster separated from a racemic ligand and is the largest supertetrahedral cobalt cluster up to now. The magnetic studies reveal it behaves as a ferromagnet. Photocatalytic properties of 1 show high catalytic activities for the degradation of the highly toxic triphenyl dye crystal violet (CV) in the presence of H2O2 under visible light in aqueous solution. The degradation rate almost reach 100 % at 45 min and can maintain 98.54 % after 8 cycles.Chiral cobalt cluster: An enantioselective coordination-induced mixed-valence homochiral Co20 supertetrahedral T4 cluster based on an inner CoIII4O4 cubane and four exterior CoII4O4 cubanes was synthesized from a racemic ligand, which displays ferromagnetic behavior and high photocatalytic activity.
      PubDate: 2017-05-24T08:15:36.342772-05:
      DOI: 10.1002/chem.201700797
       
  • The Transformation of Hybrid Silica Nanoparticles from Solid to Hollow or
           Yolk-Shell Nanostructures
    • Authors: Xingwen Liu; Guangren Qian, Zheng Jiao, Minghong Wu, Haijiao Zhang
      Abstract: Here, a facile self-templating approach is presented for synthesis of hollow and yolk-shell mesoporous silica nanoparticles (HMSNs and YMSNs) through a selective etching of hybrid silica nanoparticles. The hybrid silica nanoparticles are from the co-condensation of tetraethylorthosilicate (TEOS) and N-[3-(trimethoxysilyl)propyl]ethylenediamine (TSD) by a simple one-step process. Two kinds of products including HMSNs and YMSNs can be easily prepared only by tuning the TSD amounts in the precursor. Significantly, the transformation of hollow structure does not use any sacrificial template and surface-protective agent. The etching mechanism and formation process are systematically investigated by SEM, TEM, TG, CHN elemental analysis and Si MAS NMR spectroscopy. The results reveal that the selective etching is mainly attributed to the discrepancy in density between the outer layer and inner area of hybrid silica, where its inner section is more readily dissolved while the outer shell is robust in hydrofluoric acid (HF) aqueous solution. Specifically, the new understanding is further extended to precisely prepare multi-shelled hollow/yolk-shell silica nanoparticles.Mesoporous silica nanoparticles: A facile self-templating approach is presented for synthesis of hollow/yolk-shell mesoporous silica nanoparticles (HMSNs and YMSNs) through a facile selective etching of hybrid silica nanoparticles.
      PubDate: 2017-05-24T08:15:31.459879-05:
      DOI: 10.1002/chem.201701140
       
  • Amino-Acid-Derived Naphthalenediimides as Versatile G-Quadruplex Binders
    • Authors: Dora M. Răsădean; Bin Sheng, Jyotirmayee Dash, G. Dan Pantoş
      Abstract: The design and synthesis of water soluble, amino-acid-functionalised naphthalenediimides (NDIs) as potential ligands of native G-quadruplexes is reported. The NDIs were tested on a panel of oncogene promoters, on the human telomeric sequence h-telo, and on double-stranded DNA. Out of the ligands tested, NDI 3 (Nϵ-Boc-l-lysine NDI) exhibited a highly discriminating nature by only stabilising the oncogene promoter c-kit2, which is up-regulated up to 80 % in ovarian, gastrointestinal, and breast malignancies.Selective oncogene stablilisation: Water-soluble, amino acid functionalised naphthalenediimides are potential ligands of native G-quadruplexes, and they are tested on a panel of oncogene promoters and against double-strand DNA. One of the ligands, NDI 3, exhibits a highly discriminating nature by stabilising only the oncogene promoter c-kit2, which is upregulated up to 80 % in ovarian, gastrointestinal, and breast malignancies (see figure).
      PubDate: 2017-05-24T08:15:28.539469-05:
      DOI: 10.1002/chem.201700957
       
  • Solid-State NMR Spectroscopy Proves the Presence of Penta-coordinated Sc
           Sites in MIL-100(Sc)
    • Authors: Raynald Giovine; Christophe Volkringer, Sharon E. Ashbrook, Julien Trébosc, David McKay, Thierry Loiseau, Jean-Paul Amoureux, Olivier Lafon, Frédérique Pourpoint
      Abstract: The use of advanced solid-state NMR methods, combined with first-principles calculations, highlight for the first time the formation of penta-coordinated scandium in activated Sc3BTB2 and MIL-100(Sc) MOFs upon dehydration. These coordinatively unsaturated sites correspond to the Lewis acid sites in MIL-100(Sc), responsible for its catalytic activity. More information can be found in the Full Paper by F. Pourpoint et al. (
      DOI : 10.1002/chem.201700584).
      PubDate: 2017-05-24T08:15:23.102445-05:
       
  • Rigidly Tethered Bis-phosphoric Acids: Generation of Tunable Chiral
           Fluorescent Frameworks and Unexpected Selectivity for the Detection of
           Ferric Ions
    • Authors: Frescilia Octa-Smolin; Raja Mitra, Maike Thiele, Constantin G. Daniliuc, Linda Stegemann, Cristian Strassert, Jochen Niemeyer
      Abstract: We describe the straightforward synthesis of a series of bis-phosphoric acids (R,R)-1 a–d, featuring two chiral 1,1′-binaphthyl-phosphoric acid units that are tethered by rigid, π-conjugated linkers. The nature of the linker has a profound influence on the properties of the bis-phosphoric acids, such as their self-association behavior and their interaction with metal ions. This led to the identification of one preferred bis-phosphoric acid (R,R)-1 d, which shows selective fluorescence quenching in the presence of ferric ions (Fe3+). Thus, (R,R)-1 d could be applied for the detection of Fe3+, even in the presence of a variety of other metal ions. The chiral nature of the bis-phosphoric acid enables the interaction with Fe3+ to be followed by CD spectroscopy, providing a complementary detection mode with the same probe.Iron turns me off: The preparation and analysis of a series of rigidly tethered 1,1′-binaphthyl-phosphoric acids led to the identification of a novel probe for ferric ions (see figure). The presence of Fe3+ can be detected by means of CD or fluorescence spectroscopy with high chemoselectivity.
      PubDate: 2017-05-24T07:10:39.282616-05:
      DOI: 10.1002/chem.201700954
       
  • A Designed ZnO@ZIF-8 Core–Shell Nanorod Film as a Gas Sensor with
           Excellent Selectivity for H2 over CO
    • Authors: Xiaonan Wu; Shunshun Xiong, Zhenghao Mao, Sheng Hu, Xinggui Long
      Abstract: The development of H2 gas sensors is important for H2 production as a fuel. In this work, a ZnO@ZIF-8 core–shell nanorod film is designed and synthesized as a gas sensor through a facile solution deposition process. This film shows an excellent selective response for H2 over CO. By fine-tuning the reaction conditions, a ZnO@ZIF-8 core–shell structure with a thin, fine-grain, porous ZIF-8 shell is obtained. Owing to the facile H2 penetration through the ZIF-8 thin shell (≈110 nm) and the increased oxygen vacancies for the complex film, the ZnO@ZIF-8 nanorod film shows a higher H2 sensitivity than a raw ZnO nanorod film. More importantly, the ZnO@ZIF-8 nanorod film shows no response for CO at 200 °C. Because of the fine-grain confinement of the porous ZIF-8 shell (
      PubDate: 2017-05-24T07:10:33.907455-05:
      DOI: 10.1002/chem.201700320
       
  • Synergistic Effect of a Boron-Doped Carbon-Nanotube-Supported Cu Catalyst
           for Selective Hydrogenation of Dimethyl Oxalate to Ethanol
    • Authors: Peipei Ai; Minghui Tan, Noriyuki Yamane, Guoguo Liu, Ronggang Fan, Guohui Yang, Yoshiharu Yoneyama, Ruiqin Yang, Noritatsu Tsubaki
      Abstract: Heteroatom doping is a promising approach to improve the properties of carbon materials for customized applications. Herein, a series of Cu catalysts supported on boron-doped carbon nanotubes (Cu/xB-CNTs) were prepared for the hydrogenation of dimethyl oxalate (DMO) to ethanol. The structure and chemical properties of boron-doped catalysts were characterized by XRD, TEM, N2O pulse adsorption, CO chemisorption, H2 temperature-programmed reduction, and NH3 temperature-programmed desorption, which revealed that doping boron into CNT supports improved the Cu dispersion, strengthened the interaction of Cu species with the CNT support, introduced more surface acid sites, and increased the surface area of Cu0 and especially Cu+ sites. Consequently, the catalytic activity and stability of the catalysts were greatly enhanced by boron doping. 100 % DMO conversion and 78.1 % ethanol selectivity could be achieved over the Cu/1B-CNTs catalyst, the ethanol selectivity of which was almost 1.7 times higher than that of the catalyst without boron doping. These results suggest that doping CNTs with boron is an efficient approach to improve the catalytic performance of CNT-based catalysts for hydrogenation of DMO. The boron-doped CNT-based catalyst with improved ethanol selectivity and catalytic stability will be helpful in the development of efficient Cu catalysts supported on non-silica materials for selective hydrogenation of DMO to ethanol.Better B doped: Boron doping is an efficient approach to improve the catalytic performance of carbon nanotube (CNT)-supported Cu catalysts (Cu/xB-CNTs, where x is the boric acid:CNT weight ratio in the doping process) for the hydrogenation of dimethyl oxalate (DMO) to ethanol. The Cu/1B-CNTs catalyst achieved the highest ethanol selectivity and DMO conversion, which could be attributed to high Cu dispersion, enhanced interaction of Cu species with the CNT support, appropriate distribution of Cu0 and Cu+, and suitable surface acidity.
      PubDate: 2017-05-24T07:10:28.096466-05:
      DOI: 10.1002/chem.201700821
       
  • Highly Conductive Water-Based Polymer/Graphene Nanocomposites for Printed
           Electronics
    • Authors: Apostolos Koutsioukis; Vasilios Georgakilas, Vassiliki Belessi, Radek Zboril
      Abstract: The preparation and characterization of highly conductive carbon inks is described based on nanocomposites that combine a polystyrene-acrylic resin or water-soluble polymers with a hydrophilic graphene/carbon nanotube hybrid. The water-based carbon inks showed high electrical conductivity and could be effectively used in advanced technologies such as gravure printing for printed electronics. Moreover, the conductivity was shown to be increased with a power law of the nanohybrid volume fraction, with an exponent close to that predicted from the percolation theory, indicating a limited impact of the polymer tunneling barrier on the electrical conductivity of such nanocomposites.Carbon inks: Highly conductive water-dispersible polymer nanocomposites gravure inks are produced by combining a hydrophilic graphene/carbon nanotube nanohybrid and polymers in a wide range of ratios. The electrical conductivity of the nanocomposites is increased with a power law of the nanohybrid volume fraction, with an exponent close to that predicted from the percolation theory, indicating a limited impact of the polymer tunneling barriers.
      PubDate: 2017-05-24T07:05:34.156021-05:
      DOI: 10.1002/chem.201700997
       
  • Synthesis of Mono-, Bis- and Tris(pentafluoroethyl)tin Derivatives,
           (C2F5)4−nSnXn (X=Ph, Me, Cl, Br, Cp; n=1–3)
    • Authors: Johannes Klösener; Markus Wiesemann, Mark Niemann, Beate Neumann, Hans-Georg Stammler, Berthold Hoge
      Abstract: For (pentafluoroethyl)phenylstannanes, (C2F5)4−n SnPhn (n=1–3), and dimethylbis(pentafluoroethyl)stannane, (C2F5)2SnMe2, a high yield synthesis was developed by the use of LiC2F5 as a C2F5 transfer reagent. The treatment of these products with gaseous hydrogen chloride or hydrogen bromide afforded (C2F5)4−nSnXn (X=Cl, Br; n=1–3) in good yields. The (pentafluoroethyl)stannanes were fully characterized by 1H, 13C, 19F and 119Sn NMR, IR spectroscopy and mass spectrometry. The treatment of the (pentafluoroethyl)tin halides (C2F5)4−nSnXn with 1,10-phenanthroline (phen) led to the formation of the corresponding octahedrally coordinated complexes [(C2F5)4−nSnXn(phen)], the structures of which were elucidated by X-ray diffraction analyses.The bromostannane (C2F5)3SnBr reacted with sodium cyclopentadienide to give the (η1-cyclopentadienyl)tris(pentafluoroethyl)stannane, (C2F5)3SnCp, for which single-crystal X-ray diffraction analysis could be performed. The coupling constants 1J(119Sn,13C) and 2J(119Sn,19F) of all new stannanes are strongly correlated and sensitive to the substitution pattern at the tin atom. For both coupling constants a negative sign could be assigned.Some-tin special: We present a convenient protocol for the high yield synthesis of (pentafluoroethyl)stannanes (n=1–3) by using LiC2F5. (Pentafluoroethyl)phenylstannanes are functionalized by gaseous hydrogen halides HX (X=Cl, Br) to give (pentafluoroethyl)tin halides. Their corresponding 1,10-phenanthroline (phen) complexes were structurally characterized by X-ray diffraction analysis.
      PubDate: 2017-05-24T07:05:31.376389-05:
      DOI: 10.1002/chem.201701270
       
  • Synthesis and Properties of Salicylaldehydes Fine-Tuned by Modular
           Assembly using “Plug-and-Socket”-Type Extendibility
    • Authors: Hirohiko Houjou; Yoshikazu Suzuki, Qian-Wen Shen, Isao Yoshikawa, Toshiki Mutai
      Abstract: A salicylaldehyde derivative bearing four pyridine arms, 3,5-bis(N,N-bis(2-pyridylmethyl)aminomethyl)-2,4-dihydroxybenzaldehyde (Hbpsal) as a “socket”, was prepared and used to derive a series of zinc complexes with various extra anions “plugged” into their vacant site. The crystal structure and 1H NMR spectra were noticeably influenced by the extra anions, allowing fine-tuning of the properties by “plug-and-socket”-type modification. Similar to unsubstituted salicylaldehyde, the zinc complexes reacted with primary amines to afford Schiff-base compounds. Because of the potential chirality around the coordination sphere, reaction with a chiral amine resulted in an equilibrium system between diastereomers, the potential of which as chiral sources tunable by the extra anions is discussed. Some of the complexes were further converted into zinc- or nickel-salphen (=N,N-bis(salicylidene)-1,2-phenylenediamine) complexes. The electrochemical properties of the nickel complex were slightly modified by the extra anions, whereas the photophysical properties of the zinc complex appeared unchanged.Peripherals: Salicylaldehyde provided with a “socket”-shaped zinc complex into which various extra anions can be “plugged” was developed. The prochirality around the coordination sphere demonstrated its potential as a chiral source tunable by the extra anions. The salicylaldehyde was derived to Schiff-base complexes, the electrochemistry of which was significantly influenced by the anions.
      PubDate: 2017-05-24T07:05:26.719397-05:
      DOI: 10.1002/chem.201701141
       
  • Hexakis [60]Fullerene Adduct-Mediated Covalent Assembly of Ruthenium
           Nanoparticles and Their Catalytic Properties
    • Authors: Philippe Serp; Faqiang Leng, Iann C. Gerber, Pierre Lecante, Ahmed Bentaleb, Antonio Muñoz, Beatriz M. Illescas, Nazario Martín, Georgian Melinte, Ovidiu Ersen, Hervé Martinez, M. Rosa Axet
      Abstract: The C66(COOH)12 hexa-adduct has been successfully used as a building block to construct, via carboxylate bridges, 3D networks with very homogeneous sub-1.8 nm ruthenium nanoparticles. This strategy allows the control of the interparticle distance. The obtained nanostructures are active in nitrobenzene selective hydrogenation.
      PubDate: 2017-05-24T06:21:09.773016-05:
      DOI: 10.1002/chem.201701043
       
  • The Role of the co-Activation and Ligand Functionalization in Neutral
           Methallyl Nickel(II) Catalysts for Oligomerization and Polymerization of
           Ethylene
    • Authors: Daniela E. Ortega; Diego Cortés-Arriagada, Oleksandra S. Trofymchuk, Diana Yepes, Soledad Gutierrez-Oliva, René S. Rojas, Alejandro Toro-Labbe
      Abstract: It is presented a detailed quantum chemical study analyzing the mechanism of ethylene oligomerization and polymerization by means of a family of four neutral methallyl NiII catalysts. The role of the boron co-activators [BF₃ or B(C₆F₅)₃] and ligand functionalization (in ortho or para position of the N-arylcyano moiety of the catalysts) was investigated to explain the chain length of the obtained polymers. The chain initialization proceeds with higher activation barriers for the ortho functionalized complexes (19 kcal mol¯¹) compared to the para isomers (17-18 kcal mol¯¹). Two main pathways were revealed for the chain propagation. The first pathway is preferred when using the B(C₆F₅)₃ co-activated catalyst, and it produce large chain polymers. A second pathway leads to the β-hydrogen complexes, which results in chain oligomerization; this pathway is preferred when the BF₃ co-activated catalysts are used. Otherwise, the termination of larger chains occurs via a stable hydride intermediate, which is formed with barriers of 14 kcal mol¯¹ for the B(C₆F₅)₃ co-activated catalysts. This work gives significant new insights into the mechanism whereby neutral methallyl NiII catalysts acts in oligomerization and polymerization processes, it clarifies the role of co-activation and ligand-functionalization, which are key information for further design of related catalysts.
      PubDate: 2017-05-24T05:35:27.268962-05:
      DOI: 10.1002/chem.201701571
       
  • Preparation and Characterization of Group 13 Cyanides
    • Authors: Ralf Haiges; Piyush Deokar, Monica Vasiliu, Trent H. Stein, David A. Dixon, Karl O. Christe
      Abstract: Invited for the cover of this issue is the group of Ralf Haiges at the University of Southern California. The image depicts characters from the popular web comic “Cyanide & Happiness” alongside some of the cyanide complexes synthesized. Read the full text of the article at 10.1002/chem.201700611.“Our work features a healthy mix of fundamental and applied research.” Read more about the story behind the cover in the Cover Profile and about the research itself on page ▪▪ ff. (
      DOI : 10.1002/chem.201700611).
      PubDate: 2017-05-24T05:33:58.485152-05:
       
  • Lipophilic N-hydroxyphthalimide Catalysts for the Aerobic Oxidation of
           Cumene: Towards Solvent-Free Conditions ... and Back
    • Authors: Manuel Petroselli; Lucio Melone, Massimo Cametti, Carlo Punta
      Abstract: A new class of lipophilic N-hydroxyphthalimides catalysts designed for the aerobic oxidation of cumene in solvent-free conditions were synthesized and tested. The specific strategy proposed for the introduction of lipophilic tails on the NHPI moiety leads to lipophilic catalysts which, while completely preserving the activity of the precursor, allow to conduct the catalytic oxidation in neat cumene for the very first time. The corresponding cumyl hydroperoxide is obtained in good yields (28-52%) and high selectivity (95-97%), under mild conditions. Importantly, the presence of a polar solvent is no longer required to guarantee the complete solubilization of the catalyst. On the other hand, the oxidation conducted in neat cumene unearths the unexpected necessity of using small amounts of acetonitrile in order to fully promote the hydrogen atom transfer process and prevent the catalyst from detrimental hydrogen bond (HB) driven aggregation.
      PubDate: 2017-05-24T05:30:24.671485-05:
      DOI: 10.1002/chem.201701573
       
  • Employing BINOL-Phosphoroselenoyl Chloride for Selective Inositol
           Phosphorylation and Synthesis of Glycosyl Inositol Phospholipid from
           Entamoeba histolytica
    • Authors: Toshihiko Aiba; Sae Suehara, Siew-Ling Choy, Yuuki Maekawa, Hannelore Lotter, Toshiaki Murai, Shinsuke Inuki, Koichi Fukase, Yukari Fujimoto
      Abstract: The chemical synthesis of glycosyl inositol phospholipids from Entamoeba histolytica is reported. The key feature of this synthesis is a regioselective phosphorylation reaction that occurs through desymmetrization of a myo-inositol derivative with phosphoroselenoyl chloride. A new protecting-group strategy was developed that utilizes allyl and alloc groups to synthesize complex glycolipids bearing unsaturated lipids. These developments provided an efficient synthetic route for various complex inositol phospholipids and their analogues. Furthermore, the binding affinity of the synthetic inositol phospholipids with mouse CD1d molecules has been evaluated, as well as the immunostimulatory activity.A route to glycolipids: The synthesis of glycosyl inositol phospholipids from Entamoeba histolytica is reported, the key feature of which is a regioselective phosphorylation reaction that occurs through desymmetrization of a myo-inositol derivative with phosphoroselenoyl chloride. A new protecting-group strategy was developed to synthesize complex glycolipids bearing unsaturated lipids. This provided an efficient route to various complex inositol phospholipids and their analogues.
      PubDate: 2017-05-24T05:15:26.807031-05:
      DOI: 10.1002/chem.201701298
       
  • Helically chiral peptides containing ferrocene-1,1′-diamine scaffold
           as a turn inducer
    • Authors: Lidija Barisic; Monika Kovacevic, Ivan Kodrin, Suncica Roca, Kresimir Molcanov, Yuning Shen, Bimalendu Adhikari, Heinz-Bernhard Kraatz
      Abstract: A series of peptides containing homo- and heterochiral Ala-Pro sequences attached to the turn inducing ferrocene-1,1′-diamine scaffold was synthesized. The effects of the backbone chirality and N-terminal group (Boc/Ac) on the conformational properties of the novel peptidomimetics were thoroughly explored by IR, NMR and CD spectroscopies as well as corroborated by DFT studies in solution. The most stable conformers of the homochiral peptides adopt the interstrand hydrogen bonding patterns, realized through ten- and thirteen-membered rings. The common feature of the most stable conformers of the heterochiral peptides is the adoption of the turn-like structures featuring the simultaneous intra- (seven-membered) and interstrand (sixteen-membered) hydrogen-bonded rings. An exchange of two N-terminal groups has a somewhat larger influence on the distribution of the hydrogen bonding patterns in homochiral than in heterochiral derivatives. The homochiral peptides containing pyridine moieties as metal coordination sites form 1:1 complexes with divalent metal ions including Zn2+, Cd2+, Cu2+ and Fe2+.
      PubDate: 2017-05-24T04:20:38.78881-05:0
      DOI: 10.1002/chem.201701602
       
  • Solid-State NMR Spectroscopy Proves the Presence of Penta-coordinated Sc
           Sites in MIL-100(Sc)
    • Authors: Raynald Giovine; Christophe Volkringer, Sharon E. Ashbrook, Julien Trébosc, David McKay, Thierry Loiseau, Jean-Paul Amoureux, Olivier Lafon, Frédérique Pourpoint
      Abstract: Advanced solid-state NMR methods and first-principles calculations demonstrate for the first time the formation of penta-coordinated scandium sites. These coordinatively unsaturated sites were shown during the thermal activation of scandium-based metal-organic frameworks (MOFs). A 45Sc NMR experiment allows their specific observation in activated Sc3BTB2 (H3BTB=1,3,5-tris(4-carboxyphenyl)benzene) and MIL-100(Sc) MOFs. The assignment of the ScO5 groups is supported by the DFT calculations of NMR parameters. The presence of ScO5 Lewis acid sites in MIL-100(Sc) explains furthermore its catalytic activity. The first NMR experiment to probe 13C−45Sc distances is also introduced. This advanced solid-state NMR pulse sequence allows the demonstration of the shrinkage of the MIL-100(Sc) network when the activation temperature is raised.MOF sites: Advanced solid-state NMR methods and first-principles calculations demonstrate for the first time the formation of penta-coordinated scandium sites. A 45Sc NMR experiment allows their specific observation in activated Sc3BTB2 and MIL-100(Sc) MOFs. The assignment of the ScO5 groups is supported by the DFT calculations of NMR parameters.
      PubDate: 2017-05-24T01:15:29.581199-05:
      DOI: 10.1002/chem.201700584
       
  • High-Throughput Assay for Enantiomeric Excess Determination in 1,2- and
           1,3-Diols and Direct Asymmetric Reaction Screening
    • Authors: Elena G. Shcherbakova; Valentina Brega, Vincent M. Lynch, Tony D. James, Pavel Anzenbacher
      Abstract: A simple and efficient method for determination of the yield, enantiomeric/diasteriomeric excess (ee/de), and absolute configuration of crude chiral diols without the need of work-up and product isolation in a high throughput setting is described. This approach utilizes a self-assembled iminoboronate ester formed as a product by dynamic covalent self-assembly of a chiral diol with an enantiopure fluorescent amine such as tryptophan methyl ester or tryptophanol and 2-formylphenylboronic acid. The resulting diastereomeric boronates display different photophysical properties and allow for fluorescence-based ee determination of molecules containing a 1,2- or 1,3-diol moiety. This method has been utilized for the screening of ee in a number of chiral diols including atorvastatin, a statin used for the treatment of hypercholesterolemia. Noyori asymmetric hydrogenation of benzil was performed in a highly parallel fashion with errors
      PubDate: 2017-05-23T21:20:27.779604-05:
      DOI: 10.1002/chem.201701923
       
  • New Insights of the Role of Al2O3 in the promotion of CuZnAl catalysts: a
           Model Study
    • Authors: Jun Hu; Yanying Song, Junjie Huang, Yangyang Li, Mingshu Chen, Huilin Wan
      Abstract: The Cu/Al2O3/ZnO(0001)Zn ternary model catalysts, as well as their binary ones, were prepared and characterized. It was found that Al2O3 grew on the ZnO(0001)Zn surface by a layer-by-layer model, while Cu grew on the ZnO(0001)Zn surface as tow dimensional clusters until 0.2 ML, then three dimensional clusters. Because of the layer-by-layer growth of Al2O3 on the ZnO(0001)Zn, Cu/Al2O3 can be considered without the effect of ZnO. The ternary model catalyst of Cu/Al2O3/ZnO(0001)Zn which contains all of the three parts on the surface was prepared by deposition of Cu on the surface of Al2O3/ZnO(0001)Zn. Low energy ion scattering spectra showed that Cu was preferred to locate on the interfaces of Al2O3/ZnO. Comparing to Cu/ZnO, the addition of Al2O3 obviously suppresses the reduction of copper oxides, leading to a higher concentration of Cu+. Cu clusters were found to be covered by thin ZnOx overlayers upon reducing the Cu/Al2O3/ZnO(0001)Zn by H2. Therefore, the high activity of the industry Cu/ZnO/Al2O3 catalyst may origin from the Cu+-rich Cu clusters at the interface of Al2O3/ZnO which are covered by thin ZnOx overlayers.
      PubDate: 2017-05-23T10:20:41.435866-05:
      DOI: 10.1002/chem.201701697
       
  • Inhibition of the aggregation and toxicity of the minimal amyloidogenic
           fragment of tau by its Pro-substituted analogs
    • Authors: Marina Chemerovski-Glikman; Moran Frenkel-Pinter, Amjaad Abu-Mokh, Ragad Mdah, Ehud Gazit, Daniel Segal
      Abstract: Inhibiting the toxic aggregation of amyloid-β and the tau protein, the key pathological agents involved in Alzheimer's, is a leading approach in modulating disease progression. Using an aggregative tau-derived model peptide, Ac-PHF6-NH2, we show that substitution of its amino acids with Proline, a known efficient β-breaker, reduces its self-assembly. This effect is attributed to the steric hindrance created by the Proline substitution, which results in disruption of the β-sheet formation process. Moreover, several of the Proline-substituted peptides inhibit the aggregation of Ac-PHF6-NH2 amyloidogenic peptide. Two of these modified inhibitors also disassemble pre-formed Ac-PHF6-NH2 fibrils and one inhibits its induced cytotoxicity. Taken together, our data suggest that these lead β-breaker peptides may be developed into novel Alzheimer's disease therapeutics
      PubDate: 2017-05-23T09:20:23.99174-05:0
      DOI: 10.1002/chem.201701218
       
  • Discrimination of Saccharides by a Simple Array
    • Authors: N. Maximilian Bojanowski; Markus Bender, Kai Seehafer, Uwe H. F. Bunz
      Abstract: We report the development of a two-component probe system as fluorescence turn-on assay of simple saccharides. The quenching of an anionic conjugated water-soluble polymer by a cationic quencher has been reported previously. Three different boronic acid functionalized benzyl viologens and three conjugated polymers of the poly(aryleneethynylene) type form nine non-fluorescent complexes. This small library discriminates nine different simple saccharides in aqueous solutions by fluorescence turn-on in a displacement assay. The saccharides can be discriminated and identified with this simple system.Simple sugar discrimination: A fluorescent turn-on assay, which incorporates poly(aryleneethynylene) polymers that discriminate and identify different saccharides through complex formation with different boronic acid substituted viologens, has been developed.
      PubDate: 2017-05-23T07:50:36.002076-05:
      DOI: 10.1002/chem.201700831
       
  • Phosphine-Mediated Sequential Annulation Reaction: Access to
           Functionalized Benzofurans and 4,5-Dihydrobenzofurans
    • Authors: Ling Liang; Xuelin Dong, You Huang
      Abstract: A new strategy for the facile access to multi-functionalized benzofurans and 4,5-dihydrobenzofurans has been explored. The advantages of the present protocol include readily obtainable starting materials, mild and metal-free conditions, expedient and practical processes, excellent yields, and easy scale-up. The reaction demonstrated high efficiency to construct two rings in a single step. The zwitterionic intermediate generated from the conjugated attack of PPh3 to the ene-yne-ketone was proposed to be the key intermediate toward these valuable scaffolds.Domino reaction: A new strategy for the facile access to multi-functionalized benzofurans and 4,5-dihydrobenzofurans is explored. The advantages include readily obtainable starting materials, mild and metal-free conditions, expedient and practical processes, excellent yields, and easy scale-up. The reaction demonstrates high efficiency to construct two rings in a single step.
      PubDate: 2017-05-23T07:50:33.986641-05:
      DOI: 10.1002/chem.201701026
       
  • Chemical Synthesis of Modified Hyaluronic Acid Disaccharides
    • Authors: Marco Mende; Martin Nieger, Stefan Bräse
      Abstract: Herein we report a chemical synthesis towards new modified hyaluronic acid oligomers by using only commercially available d-glucose and d-glucosamine hydrochloride. The various protected hyaluronic acid disaccharides were synthesized bearing new functional groups at C-6 of the β-d-glucuronic acid moiety with a view to structure-related biological activity tests. The orthogonal protecting group pattern allows ready access to the corresponding higher oligomers. Also, 1H NMR studies of the new derivatives demonstrated the effect of the various functional groups on the intramolecular electronic environment.Functional disaccharides: Various novel hyaluronic acid disaccharide derivatives with a distinct protecting group pattern that allows easy access to higher oligomers have been synthesized (see figure). 1H NMR studies demonstrated changes in the electronic environment within the molecules, especially at the hydrogen-bonding amide proton, that could result in new properties or biological activities of the corresponding higher oligomers.
      PubDate: 2017-05-23T07:50:27.411612-05:
      DOI: 10.1002/chem.201701238
       
  • Temporal Control over Transient Chemical Systems using Structurally
           Diverse Chemical Fuels
    • Authors: Jack Chen; Subhabrata Maiti, Ilaria Fortunati, Camilla Ferrante, Leonard J. Prins
      Abstract: The next generation of adaptive, intelligent chemical systems will rely on a continuous supply of energy to maintain the functional state. Such systems will require chemical methodology that provides precise control over the energy dissipation process, and thus, the lifetime of the transiently activated function. Herein we show the use of structurally diverse chemical fuels to control the lifetime of two different systems under dissipative conditions: transient signal generation and the transient formation of self-assembled aggregates. The energy stored in the fuels is dissipated at different rates by an enzyme, which installs a dependence of the lifetime of the active system on the chemical structure of the fuel. In the case of transient signal generation, it is shown that different chemical fuels can be used to generate a vast range of signal profiles, allowing temporal control over two orders of magnitude. Regarding self-assembly under dissipative conditions, the ability to control the lifetime using different fuels turns out to be particularly important as stable aggregates are formed only at well-defined surfactant/fuel ratios, meaning that temporal control cannot be achieved by simply changing the fuel concentration.
      PubDate: 2017-05-23T06:21:23.819772-05:
      DOI: 10.1002/chem.201701533
       
  • Li12P3N9 with Non-Condensed [P3N9]12− Rings and its High-Pressure
           Polymorph Li4PN3 with Infinite Chains of PN4-Tetrahedra
    • Authors: Wolfgang Schnick; Robin Niklaus, Eva-Maria Bertschler
      Abstract: Li12P3N9 was synthesized by solid-state reaction of Li3N and P3N5 at 790 °C. It is made up of non-condensed [P3N9]12- dreier-rings of PN4-tetrahedra. The high-pressure polymorph Li4PN3 of the latter was synthesized under high-pressure/high-temperature conditions from Li12P3N9 or LiPN2 and Li7PN4 at 6 or 7 GPa, respectively, using multianvil technique. Li4PN3 is the first lithium catena-nitridophosphate and contains PN3 zweier-chains of corner sharing PN4-tetrahedra. To confirm the structure elucidated from single-crystal X-ray data, Rietveld refinement, 6Li, 7Li and 31P solid-state NMR, FTIR spectroscopy and EDX measurements were carried out. To examine the phase transition of Li12P3N9 to Li4PN3 at 6 GPa and to corroborate the latter as the corresponding high-pressure polymorph, DFT calculations were conducted. Electronic band gap and electron localization function (ELF) calculations were carried out to elucidate the electronic properties and bonding behavior of both polymorphs.
      PubDate: 2017-05-23T06:21:21.481616-05:
      DOI: 10.1002/chem.201700979
       
  • Photo-Responsive Soft Ionic Crystals: Ion-Pairing Assemblies of Azobenzene
           Carboxylates
    • Authors: Ryohei Yamakado; Mitsuo Hara, Shusaku Nagano, Takahiro Seki, Hiromitsu Maeda
      Abstract: This report delineates the design and synthesis of negatively charged azobenzene derivatives that form photo-responsive ion-pairing assemblies. The azobenzene carboxylates possessing aliphatic chains were prepared as photo-responsive anions that promote the formation of ion-pairing dimension-controlled assemblies, including mesophases, when used in conjunction with a tetrabutylammonium (TBA) cation. The photo-responsive properties of the ion pairs and the precursory carboxylic acids in the bulk state were examined by POM and XRD, demonstrating that liquid crystal (LC)-liquid and crystal-liquid phase transitions occurred depending on the number and lengths of the aliphatic chains of each assembly. An ion pair exhibited photo-induced crystal-crystal phase transitions upon switching between two irradiation wavelengths (365/436 nm).
      PubDate: 2017-05-23T05:20:43.052895-05:
      DOI: 10.1002/chem.201701925
       
  • Noninnocent β-Diiminate Ligands: Redox Activity of a
           Bis(alkylimidazole)methane Ligand in Cobalt and Zinc Complexes
    • Authors: Pradip Ghosh; Richard Naastepad, Charl F. Riemersma, Martin Lutz, Marc-Etienne Moret, Robertus Johannes Klein Gebbink
      Abstract: A new β-diiminate ligand (the bis(1-methyl-4,5-diphenyl-1H-imidazol-2-yl)methane anion, L-) is introduced, in which the ligand framework bears an extended imidazole-based π-system in conjugation with a formal NacNac backbone. Bis-ligated transition metal complexes (Co, Zn) featuring this anionic ligand undergo a series of four consecutive single-electron oxidations that are all ligand based. The singly and doubly oxidized complexes can be synthesized on a preparative scale and have been fully characterized by various spectroscopic techniques. This is in sharp contrast to the corresponding NacNac-based complexes where only singly oxidized complexes were isolated and characterized. Single crystal X-ray structure determination revealed a correlation between the intraligand metrical parameters and the oxidation state of L-. These structural changes in the ligand framework make L- as a perceptible non-innocent ligand in contrast to NacNac type ligands.
      PubDate: 2017-05-23T05:20:28.153166-05:
      DOI: 10.1002/chem.201701215
       
  • High loading crystals of tetraaryladamantanes and the uptake and release
           of aromatic hydrocarbons from the gas phase
    • Authors: Clemens Richert; Pierre-Emmanuel Alexandre, Alexander Schwenger, Wolfgang Frey
      Abstract: Recently, a tetraphenyladamantane octamethylether was shown to encapsulate a wide range of small molecules in its crystals. Uptake and release from the liquid phase were demonstrated, and crystalline inclusion complexes were prepared that act as formulation for obnoxious reagents. Less than two equivalents of guest molecules were found in the crystal structures, though. Here we report the synthesis of 1,3,5,7-tetrakis(2,4-diethoxyphenyl)-adamantane (TEO) and twelve X-ray crystal structures that contain up to 3.5 equivalents of guest molecules. After crystallization and drying, TEO gives a material that absorbs 30 weight percent of p-xylene reversibly through the gas phase, and releases it again at 55 °C, suggesting that it may be used for the capture and release of aromatic hydrocarbons.
      PubDate: 2017-05-23T05:20:23.437417-05:
      DOI: 10.1002/chem.201701060
       
  • A novel open-framework copper borovanadate with enhanced catalytic
           performance for oxidation of benzylic C-H bond
    • Authors: Yuquan Feng; Zhiguo Zhong, Hongwei Wang, Huitao Fan, Dongqin Bi, Lu Wang, Zhengzheng Xing, Dongfang Qiu
      Abstract: A novel open-framework copper borovanadate with 6-conected topological net and 1-D 8-MR channels has been obtained for the first time. The compound not only exhibits a unique -B3O7(OH)-Cu-B(OH)3 linkage and features the largest ratio between TM2+(Cu2+) and the borovanadate anion, but also possesses enhanced catalytic performance, high recyclability and stability during the oxidations of benzylic C-H bond.
      PubDate: 2017-05-23T01:20:56.534292-05:
      DOI: 10.1002/chem.201702207
       
  • Supramolecular Amino Acid Based Hydrogels: Probing the Contribution of
           Additive Molecules using NMR Spectroscopy
    • Authors: Susana M. Ramalhete; Karol P. Nartowski, Nichola Sarathchandra, Jamie S. Foster, Andrew N. Round, Jesús Angulo, Gareth O. Lloyd, Yaroslav Z. Khimyak
      Abstract: Supramolecular hydrogels are composed of self-assembled solid networks that restrict the flow of water. l-Phenylalanine is the smallest molecule reported to date to form gel networks in water, and it is of particular interest due to its crystalline gel state. Single and multi-component hydrogels of l-phenylalanine are used herein as model materials to develop an NMR-based analytical approach to gain insight into the mechanisms of supramolecular gelation. Structure and composition of the gel fibres were probed using PXRD, solid-state NMR experiments and microscopic techniques. Solution-state NMR studies probed the properties of free gelator molecules in an equilibrium with bound molecules. The dynamics of exchange at the gel/solution interfaces was investigated further using high-resolution magic angle spinning (HR-MAS) and saturation transfer difference (STD) NMR experiments. This approach allowed the identification of which additive molecules contributed in modifying the material properties.Unravelling hierarchical self-assembly: The heterogeneous nature of supramolecular hydrogels makes them challenging materials for structure characterisation. The combination of microscopy, rheology, diffraction and advanced NMR spectroscopy methods probe the variable length scales and dynamics present in these soft materials (see picture).
      PubDate: 2017-05-23T01:20:42.422981-05:
      DOI: 10.1002/chem.201700793
       
  • Flexibility and Stability of Metal Coordination Macromolecules
    • Authors: Heyan Jiang; Diya Geng, Dapeng Liu, Nicholas Lanigan, Xiaosong Wang
      Abstract: The effect of chain structure on flexibility and stability of macromolecules containing weak P−Fe metal coordination bonds is studied. Migration insertion polymerization (MIP) of FpCXFp (1) and PR2CYPR2 (2) (Fp: CpFe(CO)2; CX and CY: alkyl spacers; P: phosphine; R: phenyl or isopropyl) generates P(1/2), in which the P−Fe and Fe−P bonds with opposite bonding direction are alternatively arranged in the backbone. On the other hand, P(FpCXP) synthesized from AB-type monomers (FpCXP) has P−Fe bonds arranged in the same direction. P(1/2) is more rigid and stable than P(FpCXP), which is attributed to the chain conformation resulting from the P−Fe bonding direction. In addition, the longer spacers render P(1/2) relatively flexible; the phenyl substituents, as compared with the isopropyl groups, improves the rigidity, thermal, and solution stability of P(1/2). It is therefore possible to incorporate weak metal coordination bonds into macromolecules with improved stability and adjustable flexibility for material processing.Nylon-like: Weak metal coordination bonds can be connected into macromolecules with varied flexibility, higher thermal and solution stability.
      PubDate: 2017-05-23T01:20:33.354672-05:
      DOI: 10.1002/chem.201701133
       
  • The Surprising Importance of Peptide Bond Contacts in Drug–Protein
           Interactions
    • Authors: Robert M. Parrish; Doree F. Sitkoff, Daniel L. Cheney, C. David Sherrill
      Abstract: The study of noncovalent interactions, notably including drug–protein binding, relies heavily on the language of localized functional group contacts: hydrogen bonding, π–π interactions, CH–π contacts, halogen bonding, etc. Applying the state-of-the-art functional group symmetry-adapted perturbation theory (F-SAPT) to an important question of chloro versus methyl aryl substitution in factor Xa inhibitor drugs, we find that a localized contact model provides an incorrect picture for the origin of the enhancement of chloro-containing ligands. Instead, the enhancement is found to originate from many intermediate-range contacts distributed throughout the binding pocket, particularly including the peptide bonds in the protein backbone. The contributions from these contacts are primarily electrostatic in nature, but require ab initio computations involving nearly the full drug–protein pocket system to be accurately quantified.F-SAPT analysis is applied to elucidate the origins of binding enhancement in Cl- versus Me-containing ligands targeting the factor Xa S1-pocket. The enhancement of Cl-containing ligands is found to arise from many separate and intermediate-range contacts throughout the S1 pocket, notably including a number of significant differential electrostatic interactions with peptide bonds. This study underscores the potential of tools such as SAPT and F-SAPT to provide insights into molecular recognition that may not be wholly intuitive.
      PubDate: 2017-05-23T01:10:31.470349-05:
      DOI: 10.1002/chem.201701031
       
  • Selective bromination of graphene oxide by Hunsdiecker reaction
    • Authors: Ondrej Jankovsky; Michal Lojka, Jan Luxa, David Sedmidubsky, Ondrej Tomanec, Radek Zboril, Martin Pumera, Zdenek Sofer
      Abstract: Halogenated graphenes have been attracting great attention in the recent years. The currently used methods are usually non-specific and halogen groups are randomly distributed over the graphene surface. The selective functionalization based on well known reaction mechanism allowed selective functionalization of graphene sheets. We show the application of Hunsdicker based reaction on the graphene oxide for selective bromination of graphene oxide. The chemical analysis using various spectroscopic methods proved a highly effective functionalization. Bromination can be carried out under mild conditions without any high temperature or high pressure treatment. The chemical modification led to introduction of up to 20 wt.% of bromine covalently bonded to graphene skeleton. Modified graphene was characterized in detail using a broad spectrum of microscopic and spectroscopic methods and no significant contamination by reaction byproducts was detected.
      PubDate: 2017-05-22T21:21:29.803588-05:
      DOI: 10.1002/chem.201702031
       
  • Artificial enzyme-based logic operations to mimic intracellular
           enzyme-participated redox balance system
    • Authors: yanyan Huang; Fang Pu, Jinsong Ren, Xiaogang Qu
      Abstract: Owning to the biocatalytic properties of artificial enzymes and the redox characteristic of glutathione, a colorimetric and resettable biological operation was successfully designed to mimic enzyme-participated redox balance in living systems. As one promising candidate of natural enzyme, artificial enzyme possesses many advantages and has been used in numerous fields. Similar to natural enzymes, communications are also present between different artificial enzymes. With the assistance of four artificial enzymes, three simple biological logic gates were fabricated to help us deepen the understanding of communications between artificial enzymes. In the presence of glutathione, the system could be easily reset without any complicated procedure. We prospect that this work may push forward the exploration of communications between different artificial enzymes and the design of novel artificial enzyme-based biological gates or nanodevices. We hope that our mimic system may help us further understand the functioning of complex biological pathways in biosystem.
      PubDate: 2017-05-22T21:15:29.01775-05:0
      DOI: 10.1002/chem.201701353
       
  • Dual-Responsive Molecular Switches based on Dithienylethene - Ru(II)
           Organometallics in self-assembled monolayers operating at low voltage
    • Authors: Andrea Mulas; Xiaoyan He, Yves-Marie Hervault, Lucie Norel, Stéphane Rigaut, Corinne Lagrost
      Abstract: Two carbon-rich ruthenium complexes bearing a dithienylethene (DTE) unit and a hexylthiol spacer were designed to be attached on gold surfaces. Both compounds display photochemically-driven switching properties, allowing reversible conversion from open to closed forms of the DTE units upon irradiation in solution. In contrast, only the bimetallic complex undergoes an efficient electrochemical ring closure at low potential, (0.5 V vs SCE), whereas the monometallic complex show a simple one electron reversible redox event. These appealing switching properties could be successfully transferred within diluted self-assembled monolayers (SAMs). Furthermore, the two immobilized organometallics exhibit fast electron transfer kinetics. Therefore, this organometallic strategy allows to obtain multifunctional surfaces with the possibility of combining switching events triggered by an electrochemical oxidation at low potential and by light at distinct wavelengths for a write-and-erase function, along with an access to different oxidation states. Importantly, a non-destructive electrochemical read-out is achieved at a sufficiently high scan rate that prevents any electrochemical closing. On the whole, the two surface-confined organometallic compounds exhibit appealing properties for application in molecular electronics.
      PubDate: 2017-05-22T12:40:54.049312-05:
      DOI: 10.1002/chem.201701903
       
  • From Ligand to Phosphor: Rapid, Machine-Assisted Syntheses of Substituted
           Iridium(III)-Pyrazolate Complexes with Tuneable Luminescence
    • Authors: Simon J. Pope; Lara Groves, Christiane Schotten, Joseph Beames, James Platts, Duncan Browne, Simon Coles, Peter Horton
      Abstract: A first generation machine-assisted approach towards the preparation of hybrid ligand/metal materials has been explored. A comparison of synthetic approaches demonstrates that incorporation of both flow chemistry and microwave heating, can be successfully applied to the rapid synthesis of a range of new phenyl-1H-pyrazoles (ppz) substituted with electron withdrawing groups (-F, -CF3, -OCF3, -SF5), and these, in turn, can be translated in to heteroleptic complexes, [Ir(ppz)2(bipy)]BF4 (bipy = 2,2'-bipyridine). Microwave-assisted syntheses for the Ir(III) complexes allows isolation of spectroscopically pure species in less than 1 hour of reaction time from IrCl3.xH2O. All of the new complexes have been explored photophysically (including nanosecond time-resolved transient absorption spectroscopy), electrochemically and by TD-DFT studies which show that the complexes possess ligand-dependent, and thus, tuneable green-yellow luminescence (500-560 nm), with quantum yields in the range 5-15 %.
      PubDate: 2017-05-22T12:40:25.291866-05:
      DOI: 10.1002/chem.201701551
       
  • Formation of Group 11 Bismuth Sulfide Nanoparticles Using Bismuth
           Dithioates under Mild Conditions
    • Authors: Dimuthu C. Senevirathna; Melissa V. Werrett, Narendra Pai, Victoria L. Blair, Leone Spiccia, Philip C. Andrews
      Abstract: The formation of mixed-metal sulfides with the general structure AgBiS2 and Cu3BiS2 by a simple two-step process utilizing bismuth dithiocarboxylates as Bi and S precursors is described. A sonochemical reaction of Bi2O3 with six different aryl dithioic acids: dithiobenzoic acid (BDT-H), 4-methoxydithiobenzoic acid (4-MBDT-H), 3-methyldithiobenzoic acid (3-MBDT-H), 2-mesitylenedithioic acid (2-MDT-H), 4-fluorodithiobenzoic acid (4-FBDT-H), and 2-thiophenedithioic acid (2-TDT-H) resulted in the corresponding complexes: [Bi(BDT)3] 1, [Bi(4-MBDT)3] 2, [{Bi(3-MBDT)3}2⋅C7H8] (32⋅C7H8), [Bi(2-MDT)3] 4, [Bi(4-FBDT)3] 5 and [Bi(2-TDT)3] 6. Microwave irradiation of these bismuth(III)aryldithioate complexes with AgNO3 or CuCl under mild reaction conditions (140 °C) resulted in the respective mixed-metal sulfides. Attempt to synthesize AuBiS2 using similar reaction protocols were unsuccessful, resulting only in the formation of elemental Au0, S8 and BiOCl.Bismuth mixed metal sulfides: The formation of AgBiS2 and Cu3BiS2 mixed-metal sulfides through a simple two-step process utilizing bismuth dithioates as single source Bi and S precursors is described. Microwave irradiation of bismuth(III)aryldithioate complexes with AgNO3 or CuCl under mild reaction conditions (140 °C) resulted in the respective mixed-metal sulfides.
      PubDate: 2017-05-22T07:45:40.242447-05:
      DOI: 10.1002/chem.201701952
       
  • Deactivation of a Cobalt Catalyst for Water Reduction through Valence
           Tautomerism
    • Authors: Habib Baydoun; Shivnath Mazumder, H. Bernhard Schlegel, Cláudio N. Verani
      Abstract: The activity of the water reduction catalyst [CoIII(L1)(pyr)2]PF6 (1), where (L1)2− is a bis-amido pyridine ligand and pyr is pyrrolidine, is investigated. Catalyst 1 has an overpotential of 0.54 V and a high observed TOF of 23 min−1, albeit for a relatively short time. Considering the significant activity of 1 and aiming to improve catalyst design, a detailed structural and electronic study is performed to understand the mechanisms of deactivation. Experimental and theoretical evidence support that the metal-reduced [CoI(L1)]− is in tautomeric equilibrium with the ligand-reduced [CoII(L1.)]− species. While [CoI(L1)]− favors formation of a CoIII−H− relevant for catalysis, the [CoII(L1.)]− species leads to ligand protonation, structural distortions, and, ultimatley, catalyst deactivation.Deactivate: A new Co-based water reduction catalyst displays a high TOF of 23 min−1, albeit for a relatively short time. A detailed structural and electronic study was performed to understand the mechanisms of deactivation and conclude that tautomeric equilibrium between [CoI(L1)]− and [CoII(L1.)]− takes place. While the [CoI(L1)]− state supports catalysis through CoIII-H− formation, the [CoII(L1.)]− state leads to catalyst deactivation. This knowledge is instrumental for the future design of robust catalysts.
      PubDate: 2017-05-22T07:45:31.12547-05:0
      DOI: 10.1002/chem.201701783
       
  • Simultaneous Triple Imaging with Two PARASHIFT Probes: Encoding
           Anatomical, pH and Temperature Information using Magnetic Resonance Shift
           Imaging
    • Authors: Katie-Louise N. A. Finney; Alice C. Harnden, Nicola J. Rogers, P. Kanthi Senanayake, Andrew M. Blamire, Dara O'Hogain, David Parker
      Abstract: The chemical shift of paramagnetically shifted resonances in lanthanide(III) complexes encodes information about temperature and has also been made to report pH in parallel, through introduction of a single phosphonate group adjacent to the reporter tert-butyl resonance. The enhanced sensitivity of this new probe has allowed the simultaneous triple imaging of the water signal and the shifted tert-butyl signals of thulium and dysprosium complexes of a common ligand, separated by over 160 ppm. In parallel spectral imaging experiments, the temperature and pH dependence of the frequency of the Tm and Dy signals has been deconvoluted, allowing the pH and temperature in the liver, kidney and bladder to be measured.The third degree: Triple imaging has been achieved (see figure), in vitro and in vivo, of the MR signal due to water and tert-butyl probe resonances of thulium and dysprosium complexes of a common ligand, permitting the simultaneous acquisition of pH and temperature of the region of interest.
      PubDate: 2017-05-22T07:40:39.923769-05:
      DOI: 10.1002/chem.201700447
       
  • pH-Responsive Aminoproline-Containing Collagen Triple Helices
    • Authors: Jasmine Egli; Christiane Siebler, Boris Maryasin, Roman S. Erdmann, Cedric Bergande, Christian Ochsenfeld, Helma Wennemers
      Abstract: pH-Responsive aminoproline residues were used to tune the stability of collagen triple helices in acidic and basic environments. The position of the aminoproline residue within the triple helix and the absolute configuration at C(4) enabled tuning of the stability over a wide range. The results open opportunities for the development of stimuli-responsive collagen-based materials. More information can be found in the Full Paper by H. Wennemers et al. (
      DOI : 10.1002/chem.201701134).
      PubDate: 2017-05-22T07:40:31.403281-05:
       
  • A novel nonmetal-containing nitric oxide releaser activatable with
           single-photon green light
    • Authors: Salvatore Sortino; Marco Blangetti, Aurore Fraix, Loretta Lazzarato, Elisabetta Marini, Barbara Rolando, Federica Sodano, Roberta Fruttero, Alberto Gasco
      Abstract: We have devised and achieved via a facile synthetic route a novel organic NO photoreleaser based on a BODIPY light harvesting antenna. This compound is stable in the dark and delivers NO under photoexcitation with the biologically favorable green light. Temporally regulated vasodilation capability is demonstrated on rat aorta by green-light-induced NO release.
      PubDate: 2017-05-22T05:20:35.190958-05:
      DOI: 10.1002/chem.201701889
       
  • αRep A3: A versatile artificial scaffold for metalloenzyme design
    • Authors: Thibault Di Meo; Wadih Ghattas, Christian Herrero, Christophe Velours, Philippe Minard, Jean-Pierre Mahy, Rémy Ricoux, Agathe Urvoas
      Abstract: αRep is a new family of artificial proteins based on a thermostable alpha-helical repeated motif. One of its members, αRep A3, forms a stable homo-dimer with a wide cleft that is able to receive metal complexes and thus appears as suitable for generating new artificial biocatalysts. Based on the crystal structure of αRep A3, two positions (F119 and Y26) were chosen and changed independently into cysteine residues. A phenanthroline ligand was covalently attached to the unique cysteine of each protein variant and the corresponding biohybrids were purified and characterized. Once mutated and coupled to phenanthroline, the protein remained folded and dimeric. Copper(II) was bound specifically by the two biohybrids with two different binding modes and, in addition, the holo biohybrid A3F119NPH was found to be able to catalyze enantioselectively the Diels-Alder (D-A) cycloaddition with up to 62% ee. This study validates the choice of the αRep A3 dimer as a protein scaffold and provides a new promising route for the design and production of new enantioselective biohybrids based on entirely artificial proteins issued from a highly diverse library.
      PubDate: 2017-05-22T05:20:32.038505-05:
      DOI: 10.1002/chem.201701518
       
  • PCR Incorporation of Polyoxometalate Modified Deoxynucleotide
           Triphosphates and Their Application in Molecular Electrochemical Sensing
           of Yersinia pestis
    • Authors: Ciara K O'Sullivan; Mayreli Ortiz, Ahmed Debela Mehdi, Marketa Svobodova, Serge Thorimbert, Denis Lasage, Richard Cole, Bernold Hasenknopf
      Abstract: Redox-labeled nucleotides are of increasing interest for the fabrication of next generation molecular tools and should meet requirements of being thermally stable, sensitive, and compatible with polymerase-mediated incorporation whilst also being electrochemically discriminable. The synthesis and characterization of Keggin and Dawson polyoxometalate-deoxynucleotide (POM-dNTP) bioconjugates linked through 7-deaza-modified purines is described. The modified POM-dNTPs were used for polymerase based amplification of a DNA sequence specific for Yersinia pestis and the amplified DNA detected via an electrochemical DNA sensor. This highlights the potential of polyoxometalates as thermally stable, sensitive and polymerase-compatible redox labels for exploitation in bioanalytical applications.
      PubDate: 2017-05-22T04:20:35.007982-05:
      DOI: 10.1002/chem.201701295
       
  • Synthesis of Benzodihydrofurans by Asymmetric C-H Insertion Reactions of
           Donor/Donor Carbenoids
    • Authors: Jared Thomas Shaw; Kellan N. Lamb, Richard A. Squitieri, Srinivasa R. Chintala, Ada J. Kwong, Edward I. Balmond, Cristian Soldi, Olga Dmytrenko, Marta Castiñeira Reis, Ryan Chung, J. Bennett Addison, James C. Fettinger, Jason C. Hein, Dean J. Tantillo, Joseph M. Fox
      Abstract: Abstract: Metal carbenoids appended with two electron-donating groups, known as "donor/donor" carbenoids, undergo diastereo- and enantioselective rhodium-catalyzed C-H insertion reactions with ether substrates to form benzodihydrofurans. Unlike the reactions of carbenoids with electron-withdrawing groups attached, the attenuated electrophilicity enables these reactions to be conducted in Lewis basic solvents (e.g., acetonitrile) and in the presence of water. The diazo precursors for these species are prepared in situ from hydrazone using a mild and chemoselective oxidant (MnO2). Although this sequence often can be performed in one-pot, control experiments have elucidated why a "two-pot" process is often more efficient. A thorough screen of achiral catalysts demonstrates that sterically-encumbered catalysts are optimal for diastereoselective reactions. Although efficient insertion into allylic and propargylic C-H bonds is observed, competing dipolar cycloaddition processes are noted for some substrates. The full substrate scope of this useful method of benzodihydrofuran synthesis, mechanisms of side reactions, and computational support for the origins of stereoselectivity are described.
      PubDate: 2017-05-22T04:20:32.557409-05:
      DOI: 10.1002/chem.201701630
       
  • Push–Pull-Type Polychlorotriphenylmethyl Radicals: New Two-Photon
           Absorbers and Dyes for Generation of Photo-Charges
    • Authors: Xiaojin Wu; Jun Oh Kim, Samara Medina, Francisco J. Ramírez, Paula Mayorga Burrezo, Shaofei Wu, Zheng Long Lim, Christoph Lambert, Juan Casado, Dongho Kim, Jishan Wu
      Abstract: Tri(4-iodo-2,3,5,6-tetrachlorophenyl)methane (2) is reported as a general building block for the synthesis of various π-conjugated polychlorotriphenylmethyl (PTM) radicals. Three push–pull-type triphenylamine-substituted PTM radicals with different substitution patterns were prepared and all exhibited intense inter-valence charge-transfer bands and large two-photon absorption (TPA) cross sections. Moreover, increase of solvent polarity also resulted in improved TPA response. The charge-transfer character of the relevant excited states provoked the efficient photo-generation of charges, anions in the PTM and cations in the amine arms, driven by the amphoteric redox character and the small coupling between donor and acceptor.Push and pull: Three triphenylamine-substituted polychlorotriphenylmethyl (PTM) radicals are prepared through a new route and their fundamental properties are studied, disclosing large two-photon absorption cross sections and fast generation of photo-charges given the appropriate design of the donor towards the PTM acceptor.
      PubDate: 2017-05-22T02:50:39.481196-05:
      DOI: 10.1002/chem.201701875
       
  • Alkyne-Substituted N-Heterophenes
    • Authors: Sebastian Hahn; Silke Koser, Manuel Hodecker, Olena Tverskoy, Frank Rominger, Andreas Dreuw, Uwe H. F. Bunz
      Abstract: The synthesis and characterization of novel S-shaped N-heterophenes is reported. The targets contain a central anthracene connected to two heterophenanthrene units. N-Heterophenes are synthesized by reacting Boldt's 1,2,6,7-anthracenetetraone with different dialkynylated ortho-diaminobenzenes. The condensation yields range from 63 to 75 %; all of the N-heterophenes are stable and isolable.S-Express: The efficient synthesis of four different S-shaped N-heterophenes by condensation of aromatic ortho-diamines with 1,2,6,7-anthracenetetraone is reported. The optical and electronic properties of the targets were evaluated and their properties are discussed through comparisons with computational studies.
      PubDate: 2017-05-22T02:50:30.690067-05:
      DOI: 10.1002/chem.201701304
       
  • A 1,2-Addition Pathway for C(sp2)−H Activation at a Dinickel Imide
    • Authors: Ian G. Powers; Cholpisit Kiattisewee, Kimberly C. Mullane, Eric J. Schelter, Christopher Uyeda
      Abstract: A dinickel imido complex was synthesized using a redox-active naphthyridine-diimine supporting ligand. Upon coordination of an external ligand, the Ni2 core was disrupted, triggering an aromatic C−H activation reaction to generate a Ni2(μ-NHAr)(Ar) species. This intermediate is capable of liberating free carbazole and phenanthridine products upon heating or treatment with excess tBuNC. Collectively, these studies establish a kinetically facile 1,2-addition mechanism for C(sp2)−H activation, taking advantage of cooperative reactivity between two Ni centers.Cooperative reactivity: An isolable dinickel nitrene complex is shown to activate aromatic C−H bonds by a 1,2-addition mechanism. Heterocyclic products can be liberated from the C−H activated intermediate through thermal or ligand-induced reductive elimination.
      PubDate: 2017-05-22T02:50:27.371034-05:
      DOI: 10.1002/chem.201701855
       
  • In Situ Formation of Co9S8/N-C Hollow Nanospheres by Pyrolysis and
           Sulfurization of ZIF-67 for High-Performance Lithium-Ion Batteries
    • Authors: Peiyuan Zeng; Jianwen Li, Ming Ye, Kaifeng Zhuo, Zhen Fang
      Abstract: Co9S8 is considered a promising candidate as the anode material in lithium-ion batteries (LIBs) because of its remarkable electrical conductivity, high theoretical capacity, and low cost. However, the practical application of Co9S8 is greatly restricted because of its poor cycling stability and rate performance, which result mainly from the large volume expansion and dissolution of the polysulfide intermediates during the charge/discharge process. In this report, Co9S8 embedded in N-rich carbon hollow spheres are successfully designed and synthesized through an in situ pyrolysis and sulfurization process, employing the well-known ZIF-67 as the precursor and ethanethiol as the sulfur source. Co9S8 nanoparticles embedded in the N-rich hollow carbon shell exhibit excellent lithium storage properties at a high charge/discharge rate. A discharge capacity of 784 mAh g−1 is obtained upon battery testing at a current density of 1 C (544 mA g−1). Even upon cycling at a current density of 4 C, the as-prepared Co9S8/N-C can still deliver a discharge capacity of 518 mAh g−1. The excellent battery performance can be attributed to the hollow structure as well as the N-rich carbon encapsulation. Moreover, this metal–organic framework sulfurization route also shows good generality for the synthesis of other metal sulfide–carbon composites such as ZnS/N-C and Cu2S/C.Better batteries: Co9S8/N-C hollow spheres were successfully synthesized through synchronous pyrolysis and sulfurization of ZIF-67 (see figure). These structures deliver a distinguished performance when applied as the anode in lithium-ion batteries.
      PubDate: 2017-05-22T02:45:38.884064-05:
      DOI: 10.1002/chem.201700881
       
  • Unprecedented Variety of Outcomes in the Oxygenation of Dinuclear
           Alkylzinc Derivatives of an N,N-Coupled Bis(β-diketimine)
    • Authors: Tomasz Pietrzak; Maciej Damian Korzyński, Iwona Justyniak, Karolina Zelga, Arkadiusz Kornowicz, Zbigniew Ochal, Janusz Lewiński
      Abstract: Reactions between O2 and organometallics with non-redox-active metal centers have received continuous interest for over 150 years, although significant uncertainties concerning the character and details of the actual mechanism of these reactions persist. Harnessing dinuclear three-coordinate alkylzinc derivatives of an N,N-coupled bis(β-diketimine) proligand (LH2) as a model system, we demonstrate for the first time that a slight modification of the reaction conditions might have a dramatic influence on the oxygenation reaction outcomes, leading to an unprecedented variety of products originating from a single reaction system, that is, partially and fully oxygenated zinc alkoxides, zinc alkylperoxides, and zinc hydroxide compounds. Our studies indicate that accessibility of the three-coordinate zinc center by the O2 molecule, coupled with the lower reactivity of Zn-Me vs. Zn-Et units towards dioxygen, are key factors in the oxygenation process, providing a novel tetranuclear methyl(methoxy)zinc {[L][ZnMe][Zn(μ-OMe]}2 and zinc ethoxide {[L][Zn(μ-OEt)]2}2. Remarkably, oxygenation of three-coordinate alkylzinc [L][ZnR]2 complexes at ambient temperature afforded a unique hydroxide {[L][Zn(μ-OH)]2}2. Oxygenation of the [L][ZnEt]2 complex in the presence of 4-methylpyridine (py-Me) at low temperature led to the isolation of a dinuclear zinc ethylperoxide [L][Zn(OOEt)(py-Me)]2, which nicely substantiates the intermediacy of an unstable zinc alkylperoxide in the formation of the subsequent zinc alkoxide and hydroxide compounds. Finally, our investigations provide compelling evidence that a non-redox-active metal center plays a crucial role in the oxygenation process through assisting in single-electron transfer from an M−C bond to an O2 molecule. Although the oxygenation of zinc alkyls occurs by radical pathways, the reported results stand in clear contradiction to the widely accepted free-radical chain mechanism.One to get them all! Harnessing dinuclear three-coordinate alkylzinc derivatives of N,N-coupled bis(β-diketimine) ligand (L) as a model system, we demonstrate for the first time that a slight modification of the reaction conditions might have a dramatic influence on the oxygenation reaction outcomes, leading to an unprecedented variety of products originating from a single reaction system, that is, partially and fully oxygenated zinc alkoxides, zinc alkylperoxides, and zinc hydroxide compounds (see scheme).
      PubDate: 2017-05-22T02:45:34.72707-05:0
      DOI: 10.1002/chem.201700503
       
  • Guanosine-5′-Monophosphate Polyamine Hybrid Hydrogels: Enhanced Gel
           Strength Probed by z-Spectroscopy
    • Authors: Raquel Belda; Enrique García-España, Gareth A. Morris, Jonathan W. Steed, Juan A. Aguilar
      Abstract: The self-assembling tendencies of guanosine-5′-monophosphate (GMP) can be drastically increased using polyamines, with potential applications in the production of biocompatible smart materials, as well as for the design of antitumor drugs based on G-quadruplex stabilization. Results from scanning electron microscopy (SEM), wide angle X-ray scattering (WAXS), rheology, and nuclear magnetic resonance (NMR) z-spectroscopy studies are presented.Some self-assembly required: The self-assembling tendencies of guanosine-5′-monophosphate (GMP) can be drastically increased using polyamines, with potential applications in the production of biocompatible smart materials, as well as in the design of antitumor drugs based on G-quadruplex stabilization.
      PubDate: 2017-05-22T02:45:29.893612-05:
      DOI: 10.1002/chem.201700642
       
  • Solvent-Regulated Self-Assembly of an Achiral Donor–Acceptor Complex in
           Confined Chiral Nanotubes: Chirality Transfer, Inversion and Amplification
           
    • Authors: Yuangang Li; Pengfei Duan, Minghua Liu
      Abstract: A chiral gelator was designed and found to form chiral nanotwists and nanotubes in toluene and DMSO, respectively, which could serve as host chiral matrices for fabricating functional soft materials. Achiral, π-conjugated donor and acceptor guests were doped into the gel, and solvent-regulated self-assembly was observed. Although both the DMSO and toluene gels containing three components look similar as transparent gels, it was clarified microscopically that, whereas achiral dopants self-assemble in the confined nanotubes in the DMSO gel, they only dissolve in the liquid phase in the toluene gel. The existence of the achiral donor and acceptor in different phases made their properties completely different. Chirality transfer occurred from the host chiral gel matrixes to guest achiral porphyrin in DMSO. Remarkably, the addition of C60 to the porphyrin/gelator gel could invert and further amplify the induced chirality of the porphyrin due to the formation of donor–acceptor pairs. On the other hand, no chirality transfer was observed in the toluene gel. These observations clearly unveiled the selective self-assembly of different components in distinct gel phases, which could provide new insight into the design of chiroptical soft materials.Chirality transferred: A chiral gelator forms chiral nanotubes and nanotwists in DMSO and toluene gels, respectively, which were doped with an achiral porphyrin. In the DMSO gel, chirality can be transferred from the gelator to porphyrin aggregates, C60 forms a sandwich complex with the porphyrin and further amplifies the chirality, whereas no chirality transfer was observed in the toluene gel (see figure).
      PubDate: 2017-05-22T02:45:26.790999-05:
      DOI: 10.1002/chem.201700613
       
  • Au(I)···Au(I) interaction assisted host-guest interactions and
           stimuli-responsive self-assembly in tetranuclear alkynylgold(I)
           calix[4]arene-based isocyanide complexes
    • Authors: Anlea Chu; Franky Ka-Wah Hau, Vivian W. W. Yam
      Abstract: Multi-stimuli-responsive tetranuclear gold(I) complexes have been prepared based on a tetra(alkynyl)calix[4]arene framework, with incorporation of a series of isocyanide ligands of tunable hydrophilicity. This class of complexes is found to exhibit high sensitivity towards group IIIA metal ions especially indium(III) ions. Drastic electronic absorption and emission changes have been observed, which could be attributed to the formation of Au(I)···Au(I) interactions during the binding event. Solvent-induced self-aggregation has also been observed upon changing the solvent environment to a more polar medium, with the formation of nanoaggregates and the turning on of the aurophilic interactions, leading to interesting luminescence and morphological changes. The aggregation process has been monitored by UV-vis absorption, emission and ¹H NMR spectroscopy and dynamic light scattering (DLS) studies, and the morphological changes have been studied by electron microscopy. This new class of complexes has shown high sensitivity towards external stimuli and demonstrated the feasibility of employing the on-off switching of aurophilicity as effective design strategy for the construction of functional supramolecular systems.
      PubDate: 2017-05-21T22:15:27.748356-05:
      DOI: 10.1002/chem.201701631
       
  • Stereospecific winding of polycyclic aromatic hydrocarbons into Trinacria
           propellers
    • Authors: Dario Mosca; Antoine Stopin, Nicola Demitri, Johan Wouters, Davide Bonifazi
      Abstract: The stereospecific trimerization of enantiomerically-pure binaphthols with hexakis(bromomethyl)benzene gives access in one step to enantiomerically-pure molecular propellers, in which three binaphthyl rings are held together through dioxecine rings. X-Ray diffraction analysis revealed that three out the six naphthyl moieties are folded in a (EF)3-type arrangement held by three intramolecular C-H…π interactions. This slips outward the three remaining naphthyl rings in a blade-like fashion, just like in three-folded propeller components. This peculiar conformation shows striking similarity to the mythological Sicilian symbol of Trinacria, from which the name "trinacria propeller" derives. The propeller conformation is also preserved in chlorinated solutions, as displayed by the presence of a peak at 4.7 ppm typical of an aromatic proton resonance engaged in a C-H…π interaction. The denaturation of the propeller-like conformation is obtained at high temperature, corresponding to activation energy for the ring inversion of ca. 18.2 kcal mol-1. Notably, halide-functionalized molecular propellers exposing I-atoms at the leading and trailing edges could be prepared stereo- and regiospecifically by choosing the relevant iodo-bearing BINOL derivative.
      PubDate: 2017-05-21T21:20:32.88136-05:0
      DOI: 10.1002/chem.201702032
       
  • Structure-induced switching of the band gap, charge order and correlation
           strength in ternary vanadium oxide bronzes
    • Authors: Thomas Tolhurst; Justin Andrews, Brett Leedahl, Peter Marley, Sarbajit Banerjee, Alexander Moewes
      Abstract: Recently, V2O5 nanowires have been synthesized as several different polymorphs, and as correlated bronzes with cations intercalated between the layers of edge- and corner-sharing VO6 octahedra. Unlike extended crystals, which tend to be plagued by substantial local variations in stoichiometry, nanowires of correlated bronzes exhibit precise charge ordering, thereby giving rise to pronounced electron correlation effects. These developments have greatly broadened the scope of research, and promise applications in several frontier electronic devices that make use of novel computing vectors. Here we present a study of δ-SrxV2O5, expanded δ-SrxV2O5, exfoliated δ-SrxV2O5 and δ-KxV2O5 using a combination of synchrotron soft x-ray spectroscopy and density functional theory calculations. We experimentally determine the band gaps of each system, and discuss their calculated electronicstructures from the perspective of the measured spectra. Band gaps ranging from 0.66 ± 0.20 eV to 2.32 ± 0.20 eV are found, and linked to the underlying structure of each material. This demonstrates that the band gap of V2O5 can be tuned across a large portion of the range of greatest interest for device applications. The potential for metal-insulator transitions, tuneable electron correlations and charge ordering in these systems is discussed within the framework of our measurements and calculations, while highlighting the structure-propertyrelationships that underpin them.
      PubDate: 2017-05-21T21:20:29.562118-05:
      DOI: 10.1002/chem.201700962
       
  • Universal Method for Large Scale Synthesis of Layered Transition Metal
           Dichalcogenides
    • Authors: Zdenek Sofer; David Sedmidubsky, Jan Luxa, Daniel Bousa, Stepan Huber, Petr Lazar, Martin Vesely, Martin Pumera
      Abstract: The layered transition metal dichalcogenides currently belong to the most intensively investigated materials. These com-pounds constitute a broad family of materials with characteristic layered structures and covering both semiconductors and metallic materials. The great attention arises from the possibility to exfoliate these materials down to single layers with many unique properties like thickness dependent energy of band gap and the possibility of tuning transport properties by phase transitions. The research in the field of transition metal dichalcogenides is also motivated by their high electrocatalytic activity towards several industrially important reactions like hydrogen evolution reaction as well as many other applications in nano- and optoelectronics. Although these materials are studied intensively, their availability is extremely limited and only disulfides of molybdenum and tungsten are commercially broadly available. We report on the optimized procedures for simple direct synthesis of transition metal dichalcogenides using powder metals and elemental chalcogens. The optimized thermal treatment allowed the synthesis scaling of the sulfides, selenides and tellurides of 4th, 5th, 6th and 7th group of layered structure dichalcogenides. The synthesized transition metal dichalcogenides were single phase. The phase purity, structure and morphology were investigated in detail by electron microscopy and EDS, X-ray diffraction and Raman spectroscopy.
      PubDate: 2017-05-20T09:50:25.18712-05:0
      DOI: 10.1002/chem.201701628
       
  • AcetylacetonateBODIPY−biscyclometalated Iridium(III) complexes:
           Effective strategy towards smarter fluorescent-photosensitizer agents
    • Authors: Maria J. Ortiz; Eduardo Palao, Rebeca Sola-Llano, Andrea Tabero, Hegoi Manzano, Antonia R Agarrabeitia, Angeles Villanueva, Iñigo López-Arbeloa, Virginia Martinez-Martinez
      Abstract: Biscyclometalated Ir(III) complexes involving BODIPY-based ancillary ligands, where the BODIPY unit is grafted to different chelating cores (acetylacetonate for Ir-1 and Ir-2, and bipyridine for Ir-3) by the BODIPY meso position, have been synthesized and characterized. Complexes having the BODIPY moiety directly grafted to acetylacetonate (Ir-1 and Ir-2) exhibit higher absorption coefficient (ca. ε = 4.46 104 M-1 cm-1 and 3.38 104 M-1cm-1 at 517 nm and 594 nm, respectively), higher moderate-fluorescence emission (ca. fluorescence quantum yield = 0.08 and 0.22 at 528 nm and 652 nm, respectively) and, especially, more efficient singlet oxygen generation upon visible-light irradiation (ca. singlet oxygen generation quantum yield = 0.86 and 0.59, respectively) than that exhibited by Ir-3 (ca. singlet oxygen generation quantum yield = 0.51, but only under UV light). Phosphorescence emission, nanosecond time-resolved transient absorption and DFT calculations suggest that BODIPY-localized long-lived 3IL states are populated for Ir-1 and Ir-2. In-vitro photodynamic therapy (PDT) activity studied for Ir-1 and Ir-2 in HeLa cells shows that such complexes are efficiently internalized into the cells, exhibiting low dark- and high photo-cytoxicity, even at significant low complex concentration, making them potentially suitable as theranostic agents.
      PubDate: 2017-05-19T09:50:44.551647-05:
      DOI: 10.1002/chem.201701347
       
  • Effects of N-Oxidation on Heteroaromatic Macrocycles: Synthesis,
           Electronic Structures, Spectral Properties, and Reactivities of
           Tetraazaporphyrin meso-N-Oxides
    • Authors: Naoyuki Toriumi; Shunsuke Yanagi, Atsuya Muranaka, Daisuke Hashizume, Masanobu Uchiyama
      Abstract: Heteroaromatic N-oxides such as pyridine and quinoline N-oxides are well studied in organic chemistry, and N-oxide formation has long been utilized for tuning the reactivities of heteroaromatics. However, the scope of aromatic N-oxidation is still restricted to relatively small azine or azole skeletons, and there has been little investigation of the photophysical/chemical effects of N-oxidation on larger heteroaromatic systems. Here, the synthesis and unique properties of new macrocyclic heteroaromatic N-oxides, tetraazaporphyrin (TAP) meso-N-oxides, are reported. N-Oxidation of TAP reduced the 18π-aromaticity of the TAP ring compared with that of the parent TAP owing to the cross-conjugated resonance structure. The optical properties of TAPs were significantly changed by N-oxidation: the N-oxides did not exhibit azaporphyrin-like but instead porphyrin-like optical properties, that is, weak Q absorption bands, strong Soret absorption bands, and weak fluorescence. These features can be explained by the near-degenerate frontier molecular orbitals resulting from N-oxide formation. Singlet oxygen quantum yields were greatly increased to almost quantitative levels by N-oxidation. The N-oxides showed near-IR-responsive photoredox properties and were suitable as both oxidants and sensitizers for oxidation reactions. Protonation of the N-oxides restored TAP-like intense Q bands and red fluorescence, offering a potential design strategy for fluorescence switches.Macrocyclic heteroaromatic N-oxides: Tetraazaporphyrin (TAP) meso-N-oxides are synthesized by direct oxidation of TAPs. The introduction of an oxygen atom significantly alters the physicochemical properties: the N-oxides exhibit weaker red/near-IR absorption and fluorescence, whereas singlet oxygen quantum yields are greatly enhanced. The N-oxides show near-IR-responsive photoredox properties, and protonation of the N-oxides restores TAP-like intense red absorption and fluorescence.
      PubDate: 2017-05-19T08:01:28.712584-05:
      DOI: 10.1002/chem.201701300
       
  • Photochemistry of 1- and 2-Naphthols and Their Water Clusters: The Role of
           1ππ*(La) Mediated Hydrogen Transfer to Carbon Atoms
    • Authors: Jurica Novak; Antonio Prlj, Nikola Basarić, Clémence Corminboeuf, Nađa Došlić
      Abstract: The computational analysis of the isomer- and conformer-dependent photochemistry of 1- and 2-naphthols and their microsolvated water clusters is motivated by their very different excited state reactivities. We present evidence that 1- and 2-naphthol follow distinct excited state deactivation pathways. The deactivation of 2-naphthols, 2-naphthol water clusters, as well as of the anti conformer of 1-naphthol is mediated by the optically dark 1πσ* state. The dynamics of the 1πσ* surface leads to the homolytic cleavage of the OH bond. On the contrary, the excited state deactivation of syn 1-naphthol and 1-naphthol water clusters follows an uncommon reaction pathway. Upon excitation to the bright 1ππ*(La) state, a highly specific excited state hydrogen transfer (ESHT) to carbon atoms C8 and C5 takes place, yielding 1,8- and 1,5-naphthoquinone methides. The ESHT pathway arises from the intrinsic electronic properties of the 1ππ*(La) state of 1-naphthols.Path to deactivation: Ab initio static and surface hopping dynamics computations show that 1- and 2-naphthol and their water clusters follow distinct excited state deactivation pathways (see scheme).
      PubDate: 2017-05-19T06:31:02.840823-05:
      DOI: 10.1002/chem.201700691
       
  • On the Effect of Native SiO2 on Si over the SPR-mediated Photocatalytic
           Activities of Au and Ag Nanoparticles
    • Authors: Jiale Wang; Isabel C. de Freitas, Tiago V. Alves, Romulo A. Ando, Zebo Fang, Pedro H. C. Camargo
      Abstract: In hybrid materials containing plasmonic nanoparticles such as Au and Ag, charge-transfer processes from and to Au or Ag can affect both activities and selectivity in plasmonic catalysis. Inspired by the widespread utilization of commercial Si wafers in surface-enhanced Raman spectroscopy (SERS) studies, we investigated herein the effect of the native SiO2 layer on Si wafers over the surface plasmon resonance (SPR)-mediated activities of the Au and Ag nanoparticles (NPs). We prepared SERS-active plasmonic comprised of Au and Ag NPs deposited onto a Si wafer. Here, two kinds of Si wafers were employed: Si with a native oxide surface layer (Si/SiO2) and Si without a native oxide surface layer (Si). This led to Si/SiO2/Au, Si/SiO2/Ag, Si/Au, and Si/Ag NPs. The SPR-mediated oxidation of p-aminothiophenol (PATP) to p,p′-dimercaptoazobenzene (DMAB) was employed as a model transformation. By comparing the performances and band structures for the Si/Au and Si/Ag relative to Si/SiO2/Au and Si/SiO2/Ag NPs, it was found that the presence of a SiO2 layer was crucial to enable higher SPR-mediated PATP to DMAB conversions. The SiO2 layer acts to prevent the charge transfer of SPR-excited hot electrons from Au or Ag nanoparticles to the Si substrate. This enabled SPR-excited hot electrons to be transferred to adsorbed O2 molecules, which then participate in the selective oxidation of PATP to DMAB. In the absence of a SiO2 layer, SPR-excited hot electrons are preferentially transferred to Si instead of adsorbed O2 molecules, leading to much lower PATP oxidation.Feeling the heat: The effect of the native SiO2 layer on Si wafer substrates was investigated towards the surface plasmon resonance (SPR)-mediated photocatalytic oxidation activity of Au and Ag nanoparticles. The SiO2 layer was crucial to achieving higher conversions. It acted to prevent the charge transfer of SPR-excited hot electrons from the nanoparticles to the Si substrate. This enabled the transfer of SPR-excited hot electrons to adsorbed O2 that subsequently participates in the oxidation of p-aminothiophenol.
      PubDate: 2017-05-19T06:30:45.496886-05:
      DOI: 10.1002/chem.201700651
       
  • Tunable GLUT–Hexose Binding and Transport via Modulation of Hexose C-3
           Hydrogen-Bonding Capabilities
    • Authors: Venkata Pavan Kumar Kondapi; Olivier-Mohamad Soueidan, Christopher I. Cheeseman, Frederick G. West
      Abstract: The importance of the hydrogen bonding interactions in the GLUT–hexose binding process (GLUT=hexose transporter) has been demonstrated by studying the binding of structurally modified d-fructose analogues to GLUTs, and in one case its transport into cells. The presence of a hydrogen bond donor at the C-3 position of 2,5-anhydro-d-mannitol derivatives is essential for effective binding to GLUT5 and transport into tumor cells. Surprisingly, installation of a group that can function only as a hydrogen bond acceptor at C-3 resulted in selective recognition by GLUT1 rather than GLUT5. A fluorescently labelled analogue clearly showed GLUT-mediated transport and low efflux properties of the probe. This study reveals that a single positional modification of a 2,5-anhydro-d-mannitol derivative is sufficient to switch its binding preference from GLUT5 to GLUT1, and uncovers general scaffolds that are suitable for the potential selective delivery of molecular payloads into tumor cells via GLUT transport machinery.A series of fructose mimics with varying functionality at C-3 was prepared. Compounds with hydrogen bond donor groups at C-3 were recognized selectively by fructose transporter GLUT5, whereas those with hydrogen bond acceptor groups at C-3 were recognized by glucose transporter GLUT1.
      PubDate: 2017-05-19T06:25:57.467235-05:
      DOI: 10.1002/chem.201701329
       
  • A Metal-Free Oxidative Dehydrogenative Diels–Alder Reaction for
           Selective Functionalization of Alkylbenzenes
    • Authors: Srimanta Manna; Andrey P. Antonchick
      Abstract: Functionalization of C(sp3)−H bonds under metal-free reaction conditions is a great challenge due to poor bond reactivity. A novel metal-free oxidative dehydrogenative Diels–Alder reaction of alkylbenzene derivatives with alkenes through C(sp3)−H bond functionalization is described. The developed oxidative method provides a straightforward approach to biologically relevant 1,4-phenanthraquinone and isoindole derivatives from readily available starting materials. Furthermore, the synthesis of nitrostyrenes from enylbenzene derivatives by selective C(sp3)−H bond functionalization has been demonstrated.Linking rings: A metal-free oxidative dehydrogenative Diels–Alder reaction of alkylbenzene derivatives with alkenes was developed. The direct functionalization of C(sp3)−H bonds of alkylbenzenes provides access to naphthalene derivatives. The broad reaction scope and application of various functional groups was shown. Furthermore, direct transformation of ethylbenzenes to nitrostyrenes was demonstrated.
      PubDate: 2017-05-19T06:25:52.74758-05:0
      DOI: 10.1002/chem.201701535
       
  • Ratiometric Hg2+/Ag+ Probes with Orange Red-White-Blue Fluorescence
           Response Constructed by Integrating Vibration-Induced Emission with an
           Aggregation-Induced Emission Motif
    • Authors: Yiru Li; Yang Liu, Haitao Zhou, Wei Chen, Ju Mei, Jianhua Su
      Abstract: Invited for the cover of this issue is the group of Ju Mei and Jianhua Su at the East China University of Science and Technology. The image depicts the highly sensitive ratiometric fluorometric probes achieved by integrating butterfly-like VIE-active luminogen with clover-shaped AIEgen. Read the full text of the article at 10.1002/chem.201700945.“This is the first attempt to integrate vibration-induced emission with aggregation-induced emission, in pursuit of highly sensitive fluorometric probes for heavy metal ions.” Read more about the story behind the cover in the Cover Profile and about the research itself on page ▪▪ ff. (
      DOI : 10.1002/chem.201700945).
      PubDate: 2017-05-19T06:25:40.832081-05:
       
  • Electrochemical Water Oxidation Catalyzed by an In Situ Generated
           α-Co(OH)2 Film on Zeolite-Y Surface
    • Authors: Suranjana Bose; Joyashish Debgupta, Rani M. Ramsundar, Samar K. Das
      Abstract: The design and synthesis of an efficient and robust water-oxidation catalyst with inexpensive materials remains an important challenge in the context of artificial photosynthesis. Herein, a simple but unique technique is reported to in situ generate a thin-film of α-Co(OH)2 on the surface of zeolite-Y [hereafter referred to as Y-α-Co(OH)2] that acts as an efficient and stable catalyst for electrochemical water oxidation in alkaline medium. Catalyst Y-α-Co(OH)2 is so stable that it retains its catalytic activity even after 2000 cyclic voltammetric cycles of water oxidation. Expectedly, the chemical composition of α-Co(OH)2 on the surface of zeolite-Y remains same as that of parent Y-α-Co(OH)2 after 2000 electrocatalytic cycles. A Tafel slope as low as 59 mV decade−1 in 0.1 m KOH (pH 13) suggests faster oxygen evolution kinetics (overpotential=329 mV; turnover frequency=0.35 mol O2 (mol Co)−1 s−1 at 1 mA cm−2) than the existing α-Co(OH)2-based electrocatalysts operating in alkaline medium.Cobalt electrocatalysis: A simple but unique technique to in situ generate a thin-film of α-Co(OH)2 on the surface of zeolite-Y that acts as an efficient and stable catalyst for electrochemical water oxidation at alkaline pH is reported. A Tafel slope of 59 mV decade−1 in 0.1 m KOH (pH 13) suggests faster oxygen evolution kinetics (overpotential=329 mV; turnover frequency=0.35 molO2 molCo−1 s−1 at 1 mA cm−2) than the existing α-Co(OH)2-based electrocatalysts operating in alkaline medium.
      PubDate: 2017-05-19T06:25:39.074803-05:
      DOI: 10.1002/chem.201700955
       
  • Boosting Vis/NIR Charge-Transfer Absorptions of Iron(II) Complexes by
           N-Alkylation and N-Deprotonation in the Ligand Backbone
    • Authors: Andreas K. C. Mengel; Christian Bissinger, Matthias Dorn, Oliver Back, Christoph Förster, Katja Heinze
      Abstract: Reversing the metal-to-ligand charge transfer (3MLCT)/metal-centered (3MC) excited state order in iron(II) complexes is a challenging objective, yet would finally result in long-sought luminescent transition-metal complexes with an earth-abundant central ion. One approach to achieve this goal is based on low-energy charge-transfer absorptions in combination with a strong ligand field. Coordinating electron-rich and electron-poor tridentate oligopyridine ligands with large bite angles at iron(II) enables both low-energy MLCT absorption bands around 590 nm and a strong ligand field. Variations of the electron-rich ligand by introducing longer alkyl substituents destabilizes the iron(II) complex towards ligand substitution reactions while hardly affecting the optical properties. On the other hand, N-deprotonation of the ligand backbone is feasible and reversible, yielding deep-green complexes with charge-transfer bands extending into the near-IR region. Time-dependent density functional theory calculations assign these absorption bands to transitions with dipole-allowed ligand-to-ligand charge transfer character. This unique geometric and electronic situation establishes a further regulating screw to increase the energy gap between potentially emitting charge-transfer states and the non-radiative ligand field states of iron(II) dyes.Blue and green iron dyes: N-deprotonation of the ligand backbone of electron-rich polypyridine ligands in push–pull substituted iron(II) complexes yields deep-green complexes with charge-transfer bands extending into the near-IR region. According to theoretical calculations, these absorption bands feature dipole-allowed ligand-to-ligand charge-transfer character (LL′CT).
      PubDate: 2017-05-19T06:25:35.206854-05:
      DOI: 10.1002/chem.201700959
       
  • Insights into trans-Ligand and Spin-Orbit Effects on Electronic Structure
           and Ligand NMR Shifts in Transition-Metal Complexes
    • Authors: Anja H. Greif; Peter Hrobárik, Martin Kaupp
      Abstract: The nature of the trans ligand influences the ligand NMR shifts in 5d transition-metal complexes, dominated by spin-orbit (SO) effects. As analyzed for various Au(I) and Pt(II) hydride complexes, an increase in trans ligand influence may even change the sign of these SO shifts from shielding to deshielding for d10 or d8 complexes, due to the destabilization of a σ(H-M-L)-type MO by stronger trans ligands and thus modified σ-/π-spinor mixing. This allows general shift predictions. More information can be found in the Full Paper by M. Kaupp et al. (
      DOI : 10.1002/chem.201700844).
      PubDate: 2017-05-19T06:25:29.860312-05:
       
  • Spin States of Homochiral and Heterochiral Isomers of [Fe(PyBox)2]2+
           Derivatives
    • Authors: Kay E. Burrows; Sarah E. McGrath, Rafal Kulmaczewski, Oscar Cespedes, Simon A. Barrett, Malcolm A. Halcrow
      Abstract: The cover image compares the molecular spin states of two diastereomers of a spin-crossover iron(II) complex. Solution-phase magnetic measurements show the low-spin state of the heterochiral (meso) diastereomer is stabilized relative to its homochiral (rac) congener. This reflects a steric clash between phenyl substituents in the rac isomer, which occupies two diagonal quadrants in the molecule. The resultant twisting of the ligand conformation and metal-coordination sphere explains the observed reduction in the ligand field. More information can be found in the Full Paper by M. A. Halcrow et al. (
      DOI : 10.1002/chem.201700820).
      PubDate: 2017-05-19T06:25:26.233184-05:
       
  • Lanthanide Ions Coupled with Photoinduced Electron Transfer Generate
           Strong Reduction Potentials from Visible Light
    • Authors: Andreas Uwe Meyer; Tomáš Slanina, Alexander Heckel, Burkhard König
      Abstract: Metal ions can have beneficial effects on photoinduced electron transfer. Merging such metal-ion-coupled electron transfer (MCET) with consecutive photoinduced electron transfer (conPET) enables the one-electron reduction of chlorobenzene with blue light in the presence of diisopropylethylamine as an electron donor. The presence of the metal ions extends the substrate scope of the photoredox catalysis to extreme reduction potentials (beyond −3 V vs. SCE).With a little help from a friend: Catalytic amounts of lanthanide salts enable metal-ion coupled consecutive electron transfer allowing reductions of chloroarenes with potentials beyond −3 V versus SCE and stabilize the photocatalyst.
      PubDate: 2017-05-19T06:21:03.411997-05:
      DOI: 10.1002/chem.201701665
       
  • Planarized and Twisted Intramolecular Charge Transfer: A Concept for
           Fluorophores Showing Two Independent Rotations in Excited State
    • Authors: Gebhard Haberhauer
      Abstract: The concept of the PLATICT state is illustrated in the image. The key element is a fluorophore containing two donor (blue) and two acceptor groups (red). Absorption of UV light leads to an intramolecular charge transfer state, which is stabilized by two independent rotations. The result is the formation of the planarized and twisted intramolecular charge transfer (PLATICT) state. Due to the twofold rotations in the excited state, the fluorescence has a very large Stokes shift. The Cover picture was designed by Gunnar Floss (floss-design). More information can be found in the Full Paper by G. Haberhauer (
      DOI : https://doi.org/10.1002/chem.201700566).
      PubDate: 2017-05-19T06:20:57.538532-05:
       
  • N-Acetonitrile Functionalized Nitropyrazoles: Precursors to Insensitive
           Asymmetric N-Methylene-C Linked Azoles
    • Authors: Dheeraj Kumar; Gregory H. Imler, Damon A. Parrish, Jean'ne M. Shreeve
      Abstract: Properties of energetic compounds obtained by linking energetic pyrazoles to tetrazoles by means of N-methylene-C bridges can be fine-tuned. Reactions of pyrazole derivatives with chloroacetonitrile followed by conversion of the cyano group to tetrazole using click reactions in the presence of zinc chloride result in asymmetric N-methylene-C bridged azole-based energetic compounds. All the compounds were thoroughly characterized by IR and NMR [1H, 13C {1H}, 15N] spectroscopy, elemental analysis, and differential scanning calorimetry (DSC), and for two compounds, further supported by single-crystal X-ray diffraction studies. Heats of formation and detonation performances were calculated using Gaussian 03 and EXPLO5 v6.01 programs, respectively. Initial studies show that this new approach is promising for synthesizing less sensitive energetic compounds with fine-tuned properties.Fine-tuning of energetic properties: Properties of energetic compounds obtained through linking energetic pyrazoles to tetrazoles by means of N-methylene-C bridges can be fine-tuned. Initial studies show that this new approach is promising for synthesizing less sensitive energetic compounds with fine-tuned properties.
      PubDate: 2017-05-19T06:20:33.736893-05:
      DOI: 10.1002/chem.201700786
       
  • Feasibility of N2 Binding and Reduction to Ammonia on Fe-Deposited MoS2 2D
           Sheets: A DFT Study
    • Authors: Luis Miguel Azofra; Chenghua Sun, Luigi Cavallo, Douglas R. MacFarlane
      Abstract: Based on the structure of the nitrogenase FeMo cofactor (FeMoco), it is reported that Fe deposited on MoS2 2D sheets exhibits high selectivity towards the spontaneous fixation of N2 against chemisorption of CO2 and H2O. DFT predictions also indicate the ability of this material to convert N2 into NH3 with a maximum energy input of 1.02 eV as an activation barrier for the first proton–electron pair transfer.Bosch–Haber alternative' Mild conditions for N2 capture and catalytic conversion into NH3 is a key priority for “green fuels” technology. DFT findings show that Fe deposited on MoS2 2D sheets selectively captures N2 gas and converts N2 into NH3 with a maximum energy input of 1.02 eV, which arises from the activation barrier for the first H+/e− pair transfer.
      PubDate: 2017-05-19T06:20:26.709217-05:
      DOI: 10.1002/chem.201701113
       
  • A Novel Electrophoretic Deposited Coordination Supramolecular Network Film
           for Detecting Phosphate and Biophosphate
    • Authors: Tianshu Chu; Feng Zhang, Yi Wang, Yangyi Yang, Seik Weng Ng
      Abstract: A series of new lanthanide coordination supramolecular networks (CSNs) based on nalidixic acid (HNA) ligand were designed and synthesized. Their crystal structures were determined by single-crystal XRD techniques. Thin films of these compounds were first successfully deposited on indium tin oxide (ITO) glass through one-step electrophoretic deposition under mild conditions. The europium CSN film exhibits intense red emission and can act as a highly sensitive luminescent sensor for H2PO4− anions and adenosine triphosphate (ATP) in aqueous solution. The limits of detection of H2PO4− and ATP can achieve 0.68 and 1.9 μm respectively. The sensing mechanism was further explored through fluorescence and UV techniques. The fabricated sensor also showed excellent selectivity towards these phosphates in the presence of other coexisting ions (F−, Cl−, Br−, I−, SO4−, CO32−, NO3−, and AcO−) without interference. Moreover, we demonstrated the feasibility of using this sensor to detect ATP in bovine serum samples, suggesting the potential value of application in real biosystems.Film sensors: A series of new lanthanide coordination supramolecular networks (CSNs) based on nalidixic acid (HNA) ligand were designed and synthesized. These CSNs formed a luminescent film upon electrophoretic deposition (see figure) and the film exhibited excellent sensitivity and selectivity towards adenosine triphosphate (ATP).
      PubDate: 2017-05-19T06:15:38.934252-05:
      DOI: 10.1002/chem.201700114
       
  • Accessing Structurally Diverse Near-Infrared Cyanine Dyes for Folate
           Receptor-Targeted Cancer Cell Staining
    • Authors: Sandra G. König; Roland Krämer
      Abstract: Expanding the bioimaging toolbox of NIR dyes: A series of structurally diverse indotricarbocyanines was prepared by one-step Pd-catalyzed C−C-coupling reactions from a chlorinated precursor dye. Absorbance maxima, fluorescence brightness, and photostability are dependent on the structure of the dyes. Conjugation of the dyes to folic acid enables the selective visualization of cancer cells. Moreover, the dye structure affects the affinity of the conjugates to the folate receptors on the cells. More information can be found in the Full Paper by R. Krämer et al. (
      DOI : 10.1002/chem.201700026).
      PubDate: 2017-05-19T06:10:49.620112-05:
       
  • Insights into trans-Ligand and Spin-Orbit Effects on Electronic Structure
           and Ligand NMR Shifts in Transition-Metal Complexes
    • Authors: Anja H. Greif; Peter Hrobárik, Martin Kaupp
      Abstract: Invited for the cover of this issue is the group of Martin Kaupp at the Technical University Berlin. The image depicts remarkably general and large trans ligand effects on NMR shifts in 5d transition-metal complexes, and their main MO origins. Read the full text of the article at 10.1002/chem.201700884.“We decided that the cover design should be based on the confrontation of weak vs. strong.” Read more about the story behind the cover in the Cover Profile and about the research itself on page ▪▪ ff. (
      DOI : 10.1002/chem.201700844).
      PubDate: 2017-05-19T06:10:39.406946-05:
       
  • Persistent Radicals of Self-assembled Benzophenone bis-Urea Macrocycles:
           Characterization and Application as a Polarizing Agent for Solid-state DNP
           MAS Spectroscopy
    • Authors: Baillie A. DeHaven; John T. Tokarski, Arthur A. Korous, Frederic Mentink-Vigier, Thomas M. Makris, Alexander M. Brugh, Malcolm D. E. Forbes, Johan van Tol, Clifford R. Bowers, Linda S. Shimizu
      Abstract: UV-irradiation of a self-assembled benzophenone bis-urea macrocycle generates μm amounts of radicals that persist for weeks under ambient conditions. High-field EPR and variable-temperature X-band EPR studies suggest a resonance stabilized radical pair through H-abstraction. These endogenous radicals were applied as a polarizing agent for magic angle spinning (MAS) dynamic nuclear polarization (DNP) NMR enhancement. The field-stepped DNP enhancement profile exhibits a sharp peak with a maximum enhancement of ϵon/off=4 superimposed on a nearly constant DNP enhancement of ϵon/off=2 over a broad field range. This maximum coincides with the high field EPR absorption spectrum, consistent with an Overhauser effect mechanism. DNP enhancement was observed for both the host and guests, suggesting that even low levels of endogenous radicals can facilitate the study of host–guest relationships in the solid-state.Macrocycle magic! Persistent organic radicals are generated upon UV-irradiation as a consequence of their self-assembled structure. The endogenous host framework radicals, present in μm quantities, are characterized and applied as a polarizing agent for magic angle spinning (MAS) dynamic nuclear polarization (DNP) NMR spectroscopy where they displayed a maximum enhancement of four for both host and guest.
      PubDate: 2017-05-19T06:10:33.619823-05:
      DOI: 10.1002/chem.201701705
       
  • Preparation and Characterization of Group 13 Cyanides
    • Authors: Ralf Haiges; Piyush Deokar, Monica Vasiliu, Trent H. Stein, David A. Dixon, Karl O. Christe
      Abstract: New binary Group 13 cyanides were prepared from the corresponding metal trifluorides [MF3] (M = Ga, In, Tl) by fluoride–cyanide exchange reactions with Me3SiCN in the presence of stoichiometric amounts of [PPh4][CN] or 2,2’-bipyridine in acetonitrile solution. Although the reaction of the metal trifluorides with Me3SiCN in acetonitrile resulted in the recovery of the starting materials, the reaction of [MF3] with Me3SiCN in pyridine (py) solution resulted in the formation of the pyridine adducts [(py)2Ga(CN)3], [(py)3In(CN)3], and [(py)2Tl(CN)3. More information can be found in the Full Paper by R. Haiges et al. (
      DOI : 10.1002/chem.201700611).
      PubDate: 2017-05-19T06:10:27.416689-05:
       
  • Cobalt-Catalyzed Alkylation of Secondary Alcohols with Primary Alcohols
           via Borrowing Hydrogen/Hydrogen Autotransfer
    • Authors: Frederik Freitag; Torsten Irrgang, Rhett Kempe
      Abstract: Alcohols are promising sustainable starting materials because they can be obtained from abundant and indigestible biomass. The substitution of expensive noble metals in catalysis by earth abundant 3d metals, such as Mn, Fe, or Co, (nonprecious or base metals) is a related key concept with respect to sustainability. Here, we report on the first cobalt-catalyzed alkylation of secondary alcohols with primary alcohols. Easy-to-synthesize and easy-to-activate PN5P-pincer-ligand-stabilized Co complexes developed in our laboratory mediate the reaction most efficiently. The catalysis is applicable to a broad substrate scope and proceeds under relatively mild conditions. We have even demonstrated the coupling of a variety of purely aliphatic alcohols with a base or nonprecious metal catalyst. Mechanistic studies indicate that the reaction follows the borrowing hydrogen or hydrogen autotransfer concept.It is all about the al[Co]hol: The first cobalt catalyst for the alkylation of secondary alcohols with primary alcohols is reported. The system requires mild conditions with a high substrate scope, even for aliphatic motifs, and yields of the isolated products of up to 80 %.
      PubDate: 2017-05-19T02:35:29.186504-05:
      DOI: 10.1002/chem.201701211
       
  • Synthesis, Structure, and Properties of Clathrate
           Si30.3(8)P15.7(8)Se7.930(3)
    • Authors: Hui Zhang; Wei Peng, Gang Mu, Tao Hu, Fuqiang Huang, Xiaoming Xie
      Abstract: The new clathrate single crystal Si30.3(8)P15.7(8)Se7.930(3) was synthesized through a solid-state reaction, and it was characterized to have a unit cell parameter a=19.7614(1) Å and belong to space group Fm3‾. In this clathrate structure, a Se1−Si3 bond forms in place of the tetrakaidecahedron structure, and pental dodecahedral cages composed of Si and P atoms encapsulate Se2, Se3, and Se4 guest atoms. Similar structures are observed in partial Te- and Ge-substituted compounds. Theoretical calculations based on an ordered formula Si32P14Se7 showed a semiconducting electronic structure with a band gap of 0.711 eV. A photoelectric response was observed in this compound at room temperature. Across the whole temperature range, this material exhibited a weak temperature-dependent diamagnetic signal, and no phase transition or thermal anomaly was observed in heat capacity measurements.Semiconducting materials: Si30.3(8)P15.7(8)Se7.930(3) and partial Te/Ge-substituted semiclathrates were synthesized and characterized (see figure). Theoretical calculations showed a semiconducting feature based on an ordered model of Si32P14Se7, and photoelectric response and diamagnetism were observed in Si30.3(8)P15.7(8)Se7.930(3).
      PubDate: 2017-05-19T02:30:47.857351-05:
      DOI: 10.1002/chem.201700972
       
  • Metal Complexes of a Redox-Active [1]Phosphaferrocenophane: Structures,
           Electrochemistry and Redox-Induced Catalysis
    • Authors: Alexander Feyrer; Markus K. Armbruster, Karin Fink, Frank Breher
      Abstract: The synthesis and characterisation of several metal complexes of a redox-active, mesityl(Mes)-substituted [1]phosphaferrocenophane, FcPMes (1), are reported. Cyclic voltammetry studies on the bimetallic complexes [M(κ1P-1)(cod)Cl] (M=Rh: 2; M=Ir: 4), [Rh(κ1P-1)2(CO)Cl] (3) and [AuCl(κ1P-1)] (5), in conjunction with DFT calculations, provided indications for a good electronic communication between the metal atoms. To confirm that the ferrocenophane unit might be able to electrochemically influence the reactivity of the coordinated transition metal, the rhodium complex 2 was employed as stimuli-responsive catalyst in the hydrosilylation of terminal alkynes. All reactions were greatly accelerated with in situ generated 2+ as a catalyst as compared to 2. Even more importantly, a markedly different selectivity was observed. Both factors were attributed to different mechanisms operating for 2 and 2+ (alternative Chalk–Harrod and Chalk–Harrod mechanism, respectively). DFT calculations revealed relatively large differences for the activation barriers for 2 and 2+ in the reductive elimination step of the classical Chalk–Harrod mechanism. Thus, the key to the understanding is a cooperative “oxidatively induced reductive elimination” step, which facilitates both a higher activity and a markedly different selectivity.Redox-induced catalysis: Bimetallic complexes of a [1]phosphaferrocenophane are reported featuring a good electronic communication between the metal atoms. A rhodium(I) complex was employed as redox-active catalyst in the hydrosilylation of terminal alkynes. Oxidatively induced reductive elimination facilitates higher activity and markedly different selectivity for the oxidised complex.
      PubDate: 2017-05-19T02:30:39.382637-05:
      DOI: 10.1002/chem.201700868
       
  • Metal Confinement through N-(9-Alkyl)fluorenyl-Substituted N-Heterocyclic
           Carbenes and Its Consequences in Gold-Catalysed Reactions Involving Enynes
           
    • Authors: Matthieu Teci; Damien Hueber, Patrick Pale, Loïc Toupet, Aurélien Blanc, Eric Brenner, Dominique Matt
      Abstract: A series of gold(I) and gold(III) complexes containing bulky bis-N,N′-(9-alkylfluorenyl) heterocyclic carbene (RF-NHC) ligands have been prepared in high yields from appropriate imidazolinium, imidazolium and benzimidazolium salts. In all complexes, the carbene ligand provides high steric protection of the Au−X bond trans to the carbenic C atom. Irrespective of the metal oxidation state, the complexes showed high efficiency in a tandem 3,3-rearrangement/Nazarov reaction of an enynyl acetate. One of the AuIII complexes, [AuCl3(RF-NHC)], was further found to be suitable for the efficient cyclisation of a propargylcarboxamide. Furthermore, unlike related NHC–gold(I) complexes based on conventional bulky N-heterocyclic carbenes (notably, 1,3-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr), 1,3-bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) and 1,3-(bis-tert-butyl)imidazol-2-ylidene (ItBu)), the studied [AuICl(RF-NHC)] complexes catalysed the conversion of a 1,6-enyne in the presence of indole into a single product; this arises from the embracing character of the ligand, which prevents indole addition on one of the catalytic intermediates. A structure/selectivity relationship was established for all carbenes tested that took into account percent buried volumes and topographic steric maps. The results illustrate the high potential of confining NHCs in organic synthesis.Hugs from NHCs: Gold(I) complexes based on N-heterocyclic carbenes (NHCs) with embracing character provide highly regioselective control of the addition of indole on a 1,6-enyne (see figure). Their performance is related to the ability of ligands to protect the gold binding site. The findings reported illustrate the high potential of confining NHCs in organic synthesis.
      PubDate: 2017-05-19T02:30:34.359307-05:
      DOI: 10.1002/chem.201701129
       
  • Straightforward Synthesis of 2- and 2,8-Substituted Tetracenes
    • Authors: Simon Woodward; Miriam Ackermann, Saurabh K. Ahirwar, Laurence Burroughs, Mary Robert Garrett, John Ritchie, Jonathan Shine, Björk Tyril, Kevin Simpson, Peter Woodward
      Abstract: A simple regiospecific route to otherwise problematic substituted tetracenes is described. The diverse cores (E)-1,2-Ar1CH2(HOCH2)C=C(CH2OH)I (Ar1=Ph, 4-MePh, 4-MeOPh, 4-FPh) and (E)-1,2-I(HOCH2)C=C(CH2OH)I, accessed from ultra-low cost HOCH2C≡CCH2OH at multi-gram scales, allow the synthesis of diol libraries (E)-1,2-Ar1CH2(HOCH2)C=C(CH2OH)CH2Ar2 (Ar2=Ph, 4-MePh, 4-iPrPh, 4-MeOPh, 4-FPh, 4-BrPh, 4-biphenyl, 4-styryl; 14 examples) by efficient Negishi coupling. Copper-catalysed aerobic oxidation cleanly provides dialdehydes (E)-1,2-Ar1CH2(CHO)C=C(CHO)CH2Ar2, which in many cases undergo titanium(IV) chloride-induced double Bradsher closure, providing a convenient method for the synthesis of regiochemically and analytically pure tetracenes (12 examples). The sequence is typically chromatography-free, scalable, efficient and technically simple to carry out.Tetracene and not hard: A procedure is reported for the preparation of substituted tetracenes from low-cost ArCH2Cl and HOCH2C≡CCH2OH. The sequence is typically chromatography-free, scalable, efficient and technically simple to carry out.
      PubDate: 2017-05-19T02:30:29.15848-05:0
      DOI: 10.1002/chem.201701170
       
  • Fluorescence-Lifetime Imaging and Super-Resolution Microscopies Shed Light
           on the Directed- and Self-Assembly of Functional Porphyrins onto Carbon
           Nanotubes and Flat Surfaces
    • Authors: Boyang Mao; David G. Calatayud, Vincenzo Mirabello, Navaratnarajah Kuganathan, Haobo Ge, Robert M. J. Jacobs, Ashley M. Shepherd, José A. Ribeiro Martins, Jorge Bernardino De La Serna, Benjamin J. Hodges, Stanley W. Botchway, Sofia I. Pascu
      Abstract: Functional porphyrins have attracted intense attention due to their remarkably high extinction coefficients in the visible region and potential for optical and energy-related applications. Two new routes to functionalised SWNTs have been established using a bulky ZnII-porphyrin featuring thiolate groups at the periphery. We probed the optical properties of this zinc(II)-substituted, bulky aryl porphyrin and those of the corresponding new nano-composites with single walled carbon nanotube (SWNTs) and coronene, as a model for graphene. We report hereby on: i) the supramolecular interactions between the pristine SWNTs and ZnII-porphyrin by virtue of π–π stacking, and ii) a novel covalent binding strategy based on the Bingel reaction. The functional porphyrins used acted as dispersing agent for the SWNTs and the resulting nanohybrids showed improved dispersibility in common organic solvents. The synthesized hybrid materials were probed by various characterisation techniques, leading to the prediction that supramolecular polymerisation and host–guest functionalities control the fluorescence emission intensity and fluorescence lifetime properties. For the first time, XPS studies highlighted the differences in covalent versus non-covalent attachments of functional metalloporphyrins to SWNTs. Gas-phase DFT calculations indicated that the ZnII-porphyrin interacts non-covalently with SWNTs to form a donor–acceptor complex. The covalent attachment of the porphyrin chromophore to the surface of SWNTs affects the absorption and emission properties of the hybrid system to a greater extent than in the case of the supramolecular functionalisation of the SWNTs. This represents a synthetic challenge as well as an opportunity in the design of functional nanohybrids for future sensing and optoelectronic applications.Supramolecular and covalent assemblies can influence the morphology and optical properties of porphyrin arrays onto flat, conductive as well as insulating surfaces, and lead to the control of SWNTs (single walled carbon nanotubes) functionalisation at the nanoscale. The synthesis of new functionalised luminescent SWNTs is reported. STED super-resolution microscopy, fluorescence-lifetime imaging as well as XPS, TCSPC (time-correlated single photon counting), UV/Vis, NMR spectroscopy, XRD, TEM and AFM probe the complexity of the emerging covalent and supramolecular aggregates.
      PubDate: 2017-05-19T02:20:42.938327-05:
      DOI: 10.1002/chem.201605232
       
  • Metal-Free Direct Alkylation of Ketene Dithioacetals via Oxidative
           C(sp2)-H/C(sp3)-H Cross-Coupling
    • Authors: Jiangwei Wen; Fan Zhang, Wenyan Shi, Aiwen Lei
      Abstract: The functionalization of internal olefins has been a challenging task in organic synthesis. This protocol provides an efficient and transition-metal-free direct oxidative C(sp2)-H/C(sp3)-H Cross-Coupling access to tetrasubstituted olefins. The push-pull effect from the polarized olefin substrates accelerate the internal olefin C-H alkylation. Importantly, the mechanism experimental results demonstrate that the alkanes C-H bond cleavage is the rate-determining step, and a radical pathway has been proposed for the alkylation reaction. Notably, the present protocol has excellent functional group tolerance and could be easily scaled up with good efficiency.
      PubDate: 2017-05-19T01:50:33.830229-05:
      DOI: 10.1002/chem.201701664
       
  • Double Activation Catalysis for α´-Alkylidene Cyclic Enones with
           Chiral Amines and Thiols
    • Authors: Ying-Chun Chen; Zhou-Xiang Wang, Zhi Zhou, Wei Xiao, Qin Ouyang, Wei Du
      Abstract: Cooperative catalysis has contributed greatly to the progress of asymmetric synthesis. Nevertheless, the double activation catalysis has been less explored, especially in a covalently tethered pattern. Here we present a double activation strategy for α´-alkylidene cyclic enone substrates with a chiral primary amine and 2-mercaptobenzoic acid, through regio- and chemoselective additions to generate the complex interrupted iminium ion species. Significantly enhanced reactivity and enantioselectivity have been observed in the β-regioselective Michael addition and Friedel-Crafts alkylation reactions with malononitriles and indoles, respectively, producing a spectrum of chiral cyclic adducts with an exo-alkylidene group. Moreover, high resolution mass spectroscopy study has finely detected a few key covalently tethered intermediates among substrates and two catalysts, which is helpful for elucidating the catalytic mechanism.
      PubDate: 2017-05-18T21:50:33.00562-05:0
      DOI: 10.1002/chem.201702183
       
  • Alkylsilyl Peroxides as Alkylating Agents in the Copper-catalyzed
           Selective mono-N-Alkylation of Primary Amides and Arylamines
    • Authors: Ryu Sakamoto; Shunya Sakurai, Keiji Maruoka
      Abstract: The copper-catalyzed selective mono-N-alkylation of primary amides or arylamines using alkylsilyl peroxides as novel alkylating agents is reported. The reaction proceeds under mild reaction conditions and exhibits a broad substrate scope with respect to the alkylsilyl peroxides as well as to the primary amides and arylamines. Mechanistic studies suggest that the present reaction should proceed through a free-radical process including alkyl radicals generated from the alkylsilyl peroxides.
      PubDate: 2017-05-18T21:50:30.261858-05:
      DOI: 10.1002/chem.201702217
       
  • N-Aryl Groups are Ubiquitous in Cross Dehydrogenative Couplings Because
           They Stabilize Reactive Intermediates
    • Authors: Althea S.-K. Tsang; A. Stephen K. Hashmi, Peter Comba, Marion Kerscher, Bun Chan, Matthew Todd
      Abstract: The mechanism of cross-dehydrogenative coupling (CDC) reactions has been examined by experimental and computational means. We have provided a rationale for the ubiquity of the N-aryl group in these reactions. The aryl substituent stabilizes two intermediates and the high-energy transition state that connects them, which together represent the rate-determining step. This knowledge has enabled us to predict new CDC substrates that react either well or poorly.
      PubDate: 2017-05-18T20:45:50.266568-05:
      DOI: 10.1002/chem.201700430
       
  • Differential Attenuation of NMR Signals by Complementary Ion-Exchange
           Resin Beads for De Novo Analysis of Complex Metabolomics Mixtures
    • Authors: Jiaqi Yuan; Bo Zhang, Rafael Bruschweiler
      Abstract: A primary goal of metabolomics is the characterization of a potentially very large number of metabolites that are part of complex mixtures. Application to biofluids and tissue samples offers insights into biochemical metabolic pathways and their role in health and disease. 1D 1H and 2D 13C-1H HSQC NMR spectra are most commonly used for this purpose. They yield quantitative information about each proton of the mixture, but not which protons belong to the same molecule. Interpretation requires the use of NMR spectral databases naturally limited to known metabolites. Here, we present a new method that uses complementary ion exchange resin beads to differentially attenuate 2D NMR cross-peaks that belong to different metabolites. Based on their characteristic attenuation patterns, cross-peaks could be clustered and assigned to individual molecules, including unknown metabolites with multiple spin systems, as demonstrated for a metabolite model mixture and E. coli cell lysate.
      PubDate: 2017-05-18T20:45:48.074188-05:
      DOI: 10.1002/chem.201701572
       
  • Metal-free Hydroalkoxylation-Formal [4+2] Cycloaddition Cascade for the
           Synthesis of Ketals
    • Authors: Santosh J. Gharpure; Santosh Kumar Nanda, Padmaja Padmaja, Yogesh Gangaram Shelke
      Abstract: A transition metal free, acid promoted cascade hydroalkoxylation-formal [4+2] cycloaddition of various alkynols with salicylaldehyde is demonstrated for the synthesis of tetrahydrofurano/pyrano-chromenes and spiroketals. In general, alkynols underwent hydroalkoxylations in an endo-dig manner when internal alkynes were used to furnish the heteroannular ketals, whereas terminal alkynes proceeded in an exo-dig fashion leading to spiroketals. The study revealed that intramolecular hydroalkoxylation of alkynols is a preferred path over a generation of oxocarbenium ion formation when coupling partner is salicylaldehyde. This metal-free transformation provides a new avenue for the stereoselective synthesis of tetrahydrofurano- and pyrano-chromenes in an expeditious manner.
      PubDate: 2017-05-18T12:46:09.295532-05:
      DOI: 10.1002/chem.201701659
       
  • Transition metal chalcogenides/graphene ensembles for light-induced energy
           applications
    • Authors: Antonia Kagkoura; Theodosis Skaltsas, Nikos Tagmatarchis
      Abstract: Recently, nanomaterials that harvest solar energy and convert it to other forms of energy are of great interest. In this context, transition metal chalcogenides (TMCs) are lately on the spotlight due to their optoelectronic properties that render them potential candidates mainly in energy conversion applications. Integration of TMCs onto a strong electron accepting material, such as graphene, yielding novel TMC/graphene ensembles is of high significance, since photoinduced charge-transfer phenomena leading to intra-ensemble charge-separation, may occur. In this review, we highlight the utility of TMCs/graphene ensembles, with a specific focus on latest trends in applications, while their synthetic routes are also discussed. Precisely, TMC/graphene ensembles are photocatalytically active and superior as compared to intact TMCs analogues, when examined toward photocatalytic H2 evolution, dye degradation and redox transformations of organic compounds. Moreover, TMC/graphene ensembles have shown excellent prospect when employed in photovoltaics and biosensing applications. Finally, the future prospects of such materials are outlined.
      PubDate: 2017-05-18T09:50:40.365169-05:
      DOI: 10.1002/chem.201700242
       
  • Bioinspired synthesis of Cu2+-modified covalent triazine framework: A new
           highly efficient and promising peroxidase mimic
    • Authors: Fanggui Ye; Yuhao Xiong, Yuemei Qin, Linjing Su
      Abstract: Artificial enzyme mimetics is an emerging field of research owing to the remarkable advantages of enzyme mimics over native enzymes, including tunable catalytic efficiencies, lower cost, ease of preparation, and excellent tolerance to reaction systems. Herein, we report an efficient peroxidase mimic based on a copper-modified covalent triazine framework (CCTF). Owing to its unique specific surface area, atomically dispersed active Cu sites, efficient electron transfer, and enhanced photo-assisted peroxidase-like activity, the CCTF showed superior peroxidase-like enzyme activity. More importantly, copper modification represents an effective route to tailor the peroxidase-like activity of the CCTF. Furthermore, the mechanism of the enhanced peroxidase-like activity and stability of the CCTF were investigated. To demonstrate proof-of-concept, the CCTF was used for colorimetric detection of H2O2 and decomposition of organic pollutants. This work provides a new strategy for the design of enzyme mimics with a broad range of potential applications.
      PubDate: 2017-05-18T02:46:41.312429-05:
      DOI: 10.1002/chem.201701513
       
  • Total synthesis of O-GalNAcylated antifreeze glycoprotein using the
           switchable reactivity of peptidyl-N-pivaloylguanidine
    • Authors: Ryo Orii; Noriko Sakamoto, Daichi Fukami, Sakae Tsuda, Masayuki Izumi, Yasuhiro Kajihara, Ryo Okamoto
      Abstract: Antifreeze glycoprotein (AFGP) is an O-glycoprotein that displays antifreeze activity through depression of the freezing point of water. GalNAc is a core sugar structure of AFGP, and contributes to induce antifreeze activity of this glycoprotein. However the general functional role that this sugar plays at the molecular level is still unknown. To elucidate this, it is essential to determine the relationship between structure and activity of O-GalNAcylated AFGP using homogeneous glycoproteins. We thus conducted total synthesis of homogeneous O-GalNAcylated AFGP by using a unique peptide derivative: peptidyl-N-pivaloylguanidine. We found that peptidyl-N-pivaloylguanidine is an "unreactive" peptide in peptide coupling reactions but is interconvertible with a "reactive" peptide-α-thioester only by a simple treatment under buffer condition. The unique switchable reactivity of peptidyl-N-pivaloylguanidine enabled us to perform an efficient sequential peptide coupling strategy. By using this strategy, we successfully synthesized various lengths of homogeneous O-GalNAcylated AFGP including 120 amino acids length having 40 O-GalNAcylation sites. The structural analysis by circular dichroism spectroscopy and evaluation of the antifreeze activity of the synthetic AFGP(GalNAc)s revealed that the simple O-glycosylation with GalNAc is essential for both structural and functional basis of AFGP to exhibit antifreeze activity.
      PubDate: 2017-05-18T00:46:13.549659-05:
      DOI: 10.1002/chem.201702243
       
  • Inorganic Colloidal Perovskite Quantum Dots Realizing Robust Solar CO2
           Reduction
    • Authors: Jungang Hou; Shuyan Cao, Yunzhen Wu, Zhanming Gao, Fei Liang, Yiqing Sun, Zheshuai Lin, Licheng Sun
      Abstract: Inorganic perovskite quantum dots as optoelectronic materials have attracted enormous attention in light harvesting and emitting devices. However, photocatalytic conversion based on inorganic perovskite halides has not been reported. Herein, we have synthesized colloidal quantum dots (QDs, 3−12 nm) of cesium lead halide perovskites (CsPbBr3) as newcomer photocatalytic materials. The bandgap energies and photoluminescence (PL) spectra are tunable over the visible spectral region by quantum size effects on an atomic scale. The increased carrier lifetime revealed by time-resolved PL spectra, indicating the efficient electron−hole separation and transfer. As expect, the CsPbBr3 QDs with the highly selectivity over 99% achieve an efficient yield rate of 20.9 μmol/g towards solar CO2 reduction. This work has opened a new avenue for inorganic colloidal perovskite materials as efficient photocatalysts to convert CO2 into valuable fuels.
      PubDate: 2017-05-17T23:15:34.510431-05:
      DOI: 10.1002/chem.201702237
       
  • The Diversity of Chemical Bonding and Oxidation States in MS4 Molecules of
           Group-8 Elements
    • Authors: Jun Li; W. H. Eugen Schwarz, Wei Huang, Ning Jiang, Ping Yang
      Abstract: The geometric and electronic ground-state structures of 30 isomers of six MS4 molecules (M = group-8 metals Fe, Ru, Os, Hs, Sm, and Pu) have been studied by using quantum-chemical density-functional and correlated wave-function approaches. The MS4 species are compared to analogous MO4 species recently investigated (Inorg. Chem. 2016, 55: 4616). Metal oxidation state (MOS) of high value 8 appears in low-spin singlet Td geometric species (Os,Hs)S4 and (Ru,Os,Hs)O4, whereas low MOS = 2 appears in high-spin septet D2d species Fe(S2)2 and (slightly excited) metastable Fe(O2)2. The ground states of all other molecules have intermediate MOS values, with S2−, S22−, S21− (and resp. O2−-, O1−, O22−, O21−) ligands bonded by ionic, covalent and correlative contributions. The well-known tendencies toward lower MOS from oxides to sulfides, from Hs to Os to Ru, and from Pu to Sm, as well as the specific behavior of Fe, are found to arise from the different atomic orbital energies and radii of the (n-1)p core and (n-1)d and (n-2)f valence shells of the metal atoms in rows n of the periodic table. The comparative results of the electronic and geometric structures of the MO4 and MS4 species provide insight into the periodicity of oxidation states and bonding.
      PubDate: 2017-05-17T20:50:31.034234-05:
      DOI: 10.1002/chem.201701117
       
  • A Retrosynthesis Approach for Biocatalysis in Organic Synthesis
    • Authors: Uwe Bornscheuer; Rodrigo O.M.A. de Souza, Leandro S.M. Miranda
      Abstract: Lead-In: For the planning of an organic synthesis route, the disconnection approach guided by retrosynthetic analysis of possible intermediates and the chemical reactions involved, back to ready available starting materials, is well established. In contrast, such concepts just get developed for biocatalytic routes. In this review we highlight functional group interconversions catalyzed by enzymes. The article is organized rather by chemical bonds formed - exemplified for C-N, C-O- and C-C-bonds - and not by enzyme classes, covering a broad range of reactions to incorporate the desired functionality in the target molecule. Furthermore, the successful use of biocatalysts, also in combination with chemical steps, is exemplified for the synthesis of various drugs and advanced pharmaceutical intermediates such as Crispine A, Sitagliptin and Atorvastatin. This review also provides some basic guidelines to choose the most appropriate enzyme for a targeted reaction keeping in mind aspects like commercial availability, cofactor-requirement, solvent tolerance, use of isolated enzymes or whole cell recombinant microorganisms aiming to assist organic chemists in the use of enzymes for synthetic applications.
      PubDate: 2017-05-17T13:40:49.244878-05:
      DOI: 10.1002/chem.201702235
       
  • Hydrogen Bond Involving Cavity NH Protons Drives Supramolecular
           Oligomerization of Amido-Corroles
    • Authors: Daniel T Gryko; Rafał Orłowski, Mariusz Tasior, Barbara Ventura, Olga Staszewska-Krajewska, Wojciech Schilf, Michał Cyrański, Łukasz Dobrzycki
      Abstract: Trans-A2B-Corroles with amide substituents at different positions versus the macrocyclic core have been synthesized. Their self-organizing properties have been comprehensively evaluated both in solid-state and in solution. The rigid arrangement of the amide functionality with the corrole ring led to the formation of strong intramolecular interactions and precluded intermolecular interactions. Replacement of sterically hindered C6F5 substituents at positions 5 and 15 with smaller electron-withdrawing CO2Me groups resulted in significant changes in the self-assembly pattern. With these substituents, tetramers formed in a crystalline state, in which one of the H-pyrrole subunits is out of the corrole plane. This allows the N-H group to form a hydrogen bond with a neighboring carbonyl group of the n-butyl amide fragment. DOSY NMR studies showed that amido-corroles bearing the OCH2CONHn-Bu motif formed dimers in mM solutions in non-polar solvents and the dimers existed in equilibrium with monomers. However, the corroles possessing meso-esters groups did not form dimers, in polar tetrahydrofuran. Comprehensive optical studies allowed to characterize absorption and emission features of the monomer corroles in diluted solutions.
      PubDate: 2017-05-17T11:45:31.290111-05:
      DOI: 10.1002/chem.201701674
       
  • Unraveling the Coulombic forces in electronically decoupled bichromophoric
           systems during two successive electron transfers
    • Authors: Maxim Ivanov; Shriya Wadumethrige, Denan Wang, Rajendra Rathore
      Abstract: Coulombic forces are vital in modulating the electron transfer dynamics in both synthetic and biological polychromophoric assemblies, yet quantitative studies of the impact of such forces are rare, as it is difficult to disentangle electrostatic forces from electronic coupling. To address this problem, herein we assess the impact of Coulombic interactions in the successive removal of two electrons from spirobifluorenes, where the electronic coupling is nonexistent. By varying the separation between a pair of fluorenes using model compounds, ion pairing, and solvation, we find that these interactions, with energies up to ~0.4 V, switch off at ~9 Å. These findings can be (quantitatively) applied for the design of polychromophoric assemblies where the redox properties of donors and/or acceptors can be tuned by judicious positioning of the charged groups to control the (long-range) electron-transfer dynamics, for potential applications in photovoltaics and biological electron transfer.
      PubDate: 2017-05-17T09:46:12.147371-05:
      DOI: 10.1002/chem.201702211
       
  • Base-modified nucleic acids as a powerful tool for synthetic biology and
           biotechnology
    • Authors: Elena Eremeeva; Michail Abramov, Lia Margamuljana, Piet Herdewijn
      Abstract: The ability of various nucleoside triphosphate analogs of deoxyguanosine and deoxycytidine with 7-deazadeoxyadenosine (A1) and 5-chlorodeoxyuridine (T1) to serve as substrates for Taq DNA polymerase was evaluated. The triphosphate set constituted of A1, T1, and 7-deazadeoxyguanosine with either 5-methyldeoxy-cytidine or 5-fluorodeoxycytidine was successfully employed in the polymerase chain reaction (PCR) of 1.5 kb fragments as well as random oligonucleotide libraries. Another effective combination of triphosphates for the synthesis of 1 kb PCR product was A1, T1, deoxyinosine, and 5-bromodeoxycytidine. In vivo experiments using an antibiotic-resistant gene containing the latter set demonstrated that the bacterial machinery accepts fully modified sequences as genetic templates. Moreover, the ability of the base-modified segments to selectively protect DNA from cleavage by restriction endonucleases was shown. This evidence can be used to regulate the endonuclease cleavage pattern.
      PubDate: 2017-05-17T09:45:43.231499-05:
      DOI: 10.1002/chem.201700679
       
  • Synthesis of BODIPY-Labelled Cholesterylated Glycopeptides by Tandem Click
           Chemistry for Glycocalyxification of Giant Unilamellar Vesicles (GUVs)
    • Authors: Nicolai Stuhr-Hansen; Charikleia-Despoina Vagianou, Ola Blixt
      Abstract: The glycocalyx cover membrane surfaces of all living cells. These complex archtechtures render their interaction mechanisms on the membrane surface difficult to study. Artificial cell-sized membranes with selected and defined glycosylation patterns may serve as a minimalistic approach to systematically study cell surface glycan interactions. Here we developed a facile general synthetic procedure for the synthesis of BODIPY-labelled cholesterylated glycopeptides, which can coat cell-size giant unilamellar vesicles (GUVs). These peptide constructs were synthesized by SPPS using cholesterylated Fmoc-amino acids followed by tandem click reactions; firstly attaching a BODIPY-bicyclononyne (BCN) (prepared by Mitsunobu chemistry via novel aryl BCN-ethers) in absence of a catalyst and secondly by copper(I) catalyzed click reaction of an azidoglycan. Seven different GUV-glycoforms were prepeared and four of these were evaluated with their corresponding four specific anti-glycan binding lectins.
      PubDate: 2017-05-17T09:45:32.068615-05:
      DOI: 10.1002/chem.201702104
       
  • Preparation of Mesoporous Basic Mixed Metal Oxides through Assembly of
           Monodispersed Mg-Al Layered Double Hydroxide Nanoparticles
    • Authors: Yuya Oka; Yoshiyuki Kuroda, Takamichi Matsuno, Keigo Kamata, Hiroaki Wada, Atsushi Shimojima, Kazuyuki Kuroda
      Abstract: Mesoporous basic Mg-Al mixed metal oxides (MMOs) with a high surface area and large pore size were prepared through the assembly of monodispersed layered double hydroxide nanoparticles (LDHNPs) with block copolymer templates. The particle sizes of the LDHNPs were controlled mainly by varying the concentration of tris(hydroxymethyl)aminomethane (THAM), which was used as a surface stabilizing agent for the LDHNPs. LDHNPs and micelles of a block copolymer (Pluronic F127) were assembled to form a composite. The composites were calcined to transform them into mesoporous MMOs and remove the templates. The Brunauer-Emmett-Teller surface areas, mesopore sizes, and pore volumes increased as a result of using the templates. Moreover, the pore sizes of the mesoporous MMOs were controlled by using LDHNPs with different sizes. The mesoporous MMOs prepared from the LDHNPs showed much higher catalytic activity than a conventional MMO catalyst for the Knövenagel condensation of ethyl cyanoacetate with benzaldehyde. The mesoporous MMO catalyst prepared using the smallest LDHNPs, ca. 12 nm in size, showed the highest activity. Therefore, the use of monodispersed LDHNPs and templates is effective for preparing highly active mesoporous solid base catalysts.
      PubDate: 2017-05-17T09:45:27.009184-05:
      DOI: 10.1002/chem.201701282
       
  • Competition vs Cooperation in Catalytic Hydrogelators for anti-selective
           Mannich Reaction
    • Authors: Nishant Singh; Beatriu Escuder
      Abstract: Chemical systems find similarities in different sociological and biological processes where the entities compete or cooperate for a favourable outcome. This stochastic innovation mechanism of structural and functional adaptation especially in catalysis is based on factors like abundance of substrates, stability of transition state and structural/functional attributes of catalysts. Here we show how catalytic fibres of two self-sorting hydrogelators compete for the same resources to bring down the overall selectivity of Mannich reaction. Whereas, in a sol-gel system of the same molecules, the catalytically inefficient soluble molecules tend to cooperate with the fibres of other dominant catalyst for a mutually favourable catalysis. The available options for the molecules here are to carry out the reaction independently or in conjunction. However, these options are chosen based on the efficiency, selectivity and mobility of catalysts finding origin in their abilities to self-assemble.
      PubDate: 2017-05-17T05:45:34.63218-05:0
      DOI: 10.1002/chem.201701724
       
  • Efficient Fusion of Liposomes by Nucleobase Quadruple-Anchored DNA
    • Authors: Andreas Herrmann; Zhuojun meng, jian yang, qing liu, Jan Willem de Vries, Agnieszka Gruszka, Alberto Rodrίguez-Pulido, Bart Crielaard, Alexander Kros
      Abstract: Anchoring DNA via hydrophobic units into the membrane of vesicles allows tagging of these nanocontainers with sequence information. Moreover, the hybridization of DNA on the surface of liposomes enables sequence specific functionalization, vesicle aggregation and vesicle fusion. Especially, DNA hybridization-based approaches for fusion employing oligonucleotides terminally modified with one or two anchoring units were hindered by a limited degree of full fusion or by significant leakage during fusion. The current work deals with a new strategy for anchoring oligonucleotides on a membrane by lipid-modified nucleobases rather than by attaching hydrophobic units to the 3'- or 5'-termini. The lipid anchors were incorporated into the DNA sequence via phosphoramidite nucleotide building blocks during automated solid phase synthesis allowing variation of the number and position of hydrophobic units along the DNA backbone. Single-stranded DNA functionalized with four lipid-modified nucleobases was stably grafted onto the membrane of lipid vesicles. It was found that the orientation of DNA hybridization and the number of anchoring units play a crucial role in liposomal fusion, which in the most efficient system reached remarkable 29% content mixing without notable leakage.
      PubDate: 2017-05-17T05:45:29.853547-05:
      DOI: 10.1002/chem.201701379
       
  • Protein Reduction and Dialysis-Free Work-Up Through Phosphines Immobilized
           on a Magnetic Support: TCEP-Functionalized Carbon-Coated Cobalt
           Nanoparticles
    • Authors: Adrian Zwyssig; Elia M Schneider, Martin Zeltner, Balder Rebmann, Vladimir Zlateski, Robert N Grass, Wendelin Jan Stark
      Abstract: Tris(2-carboxyethyl)phosphine (TCEP) is an often used reducing agent in biochemistry due to its selectivity towards disulfide bonds. As TCEP causes undesired consecutive side reactions in various analysis methods (i.e. gel electrophoresis, protein labeling), it is usually removed via dialysis or gel filtration. Herein, an alternative method of separation is presented, namely the immobilization of TCEP on magnetic nanoparticles. This magnetic reagent provides a simple and rapid approach to remove the reducing agent after successful reduction. High reducing capacities up to 70 μmol per gramm of particles were achieved by using surface-initiated atom transfer polymerization.
      PubDate: 2017-05-17T04:46:05.274268-05:
      DOI: 10.1002/chem.201701162
       
  • Role of Halide Ions on the Nature of Magnetic Anisotropy in Tetrahedral
           Co(II) Complexes
    • Authors: Maheswaran Shanmugam; Shefali Vaidya, Saurabh Kumar Singh, Pragya Shukla, Kamaluddin Ansari, Gopalan Rajaraman
      Abstract: A family tetrahedral Co(II) complexes with molecular formula of [CoL2X2] (where L= thiourea and X = Cl (1), Br (2) and I (3)) were isolated. Detailed dc susceptibility (χMT(T) and M(H)) and its slow relaxation of magnetization measurements were performed on all the three complexes. The experimental dc magnetic data is excellently reproduced by fitting both χMT(T) and M(H) simultaneously using the parameters D = +10.8 cm-1, g1 = 2.2, g2 = 2.2, and g3 = 2.4 for 1; D = -18.7 cm-1, giso = 2.21 for 2; D = -19.3 cm-1, giso = 2.3 for 3. The replacement of Cl- anion in 1 by Br- or I- accompanied by not only change in sign of magnetic anisotropy (D), but also in magnitude. Among all the three complexes, only complex 1 shows field induced SIM behaviour. To understand the unusual magnetization relaxation phenomenon detailed ab initio CASSCF/NEVPT2 calculations are performed. The computed spin Hamiltonian parameters are in good agreement with experimental data. Particularly calculations unveil the role of halogen atom in switching the sign of D as we move from -Cl- to -I-. Large spin-orbit coupling constant associated with the heavier halide ion and weaker π donation reduces the ground state-excited state gap leads to larger contribution to negative D for the complex 3 compared to complex 1. Further magneto-structural D correlations are developed to understand the role of structural distortion on the sign and magnitude of D values in this family of complexes.
      PubDate: 2017-05-17T01:46:23.862073-05:
      DOI: 10.1002/chem.201606031
       
  • Fluorinated Porous Conjugated Polyporphyrins via Direct C-H Arylation
           Polycondensation: Preparation, Porosity, and Heterogeneous Catalyst for
           Baeyer-Villiger Oxidation
    • Authors: Qiang Cao; Qing Yin, Qi Chen, Zhi-Bing Dong, Bao-Hang Han
      Abstract: Considering high reactivity of fluorinated Fe-porphyrin and good stability of porphyrin-based porous polymer, fluorinated Fe-porphyrin conjugated porous polymers (FPOP-3~6) were synthesized through direct C-H arylation polymerization and well characterized. The obtained materials are chemically and thermally stable, in which FPOP-3 exhibits the highest Brunauer-Emmett-Teller specific surface area (about 840 m g). For function studies of the obtained polymers as heterogeneous catalyst, catalytic transformation of cycloketones to lactone by oxygen via Baeyer-Villiger oxidation was used as a model reaction. Fluorinated phenyl substituents of the Fe-porphyrin are not only beneficial to the conversion, but also can stabilize porphyrin to restrain the catalyst breakdown. FPOP-3 with high porosity exhibits the best catalytic efficiency and recycling effect. The recovered catalyst also shows good catalytic activities after three times recycling with small loss in yields.
      PubDate: 2017-05-17T01:46:14.7227-05:00
      DOI: 10.1002/chem.201700916
       
  • Cover Picture: Structural Studies of Nicotinoids: Cotinine versus Nicotine
           (Chem. Eur. J. 30/2017)
    • Authors: Iciar Uriarte; Cristóbal Pérez, Elena Caballero-Mancebo, Francisco J. Basterretxea, Alberto Lesarri, José A. Fernández, Emilio J. Cocinero
      Pages: 7154 - 7154
      Abstract: The ultimate battle has begun: The two opponents will pit their skills against each other in terms of ring puckering, intra-molecular interactions and internal rotation. The battlefield: the interaction-free environment of a supersonic expansion where both nicotinoids display their intrinsic properties. The referee: high resolution microwave spectroscopy, the perfect tool to tackle the gas-phase structure of these biomolecules. More information can be found in the Full Paper by M. J. Cocinero et al. on page 7238.
      PubDate: 2017-03-30T03:12:28.569443-05:
      DOI: 10.1002/chem.201701075
       
  • Inside Cover: Formation of δ-Lactones with anti-Baeyer–Villiger
           Regiochemistry: Investigations into the Mechanism of the Cerium-Catalyzed
           Aerobic Coupling of β-Oxoesters with Enol Acetates (Chem. Eur. J.
           30/2017)
    • Authors: Irina Geibel; Anna Dierks, Thomas Müller, Jens Christoffers
      Pages: 7155 - 7155
      Abstract: δ-Lactones with anti-Baeyer–Villiger regiochemistry are formed by aerobic, cerium-catalyzed umpolung reactions. A mechanistic proposal involving an oxycarbenium ion intermediate is supported by kinetics of the reaction (Hammett plot). Furthermore, a conformational analysis obtained by DFT calculations explains the anti-Baeyer–Villiger regiochemistry of the rearrangement reaction by a primary stereoelectronic effect. More information can be found in the Full Paper by J. Christoffers, et al. on page 7245.
      PubDate: 2017-03-30T03:11:09.667235-05:
      DOI: 10.1002/chem.201701039
       
  • Structural Studies of Nicotinoids: Cotinine versus Nicotine
    • Authors: Iciar Uriarte; Cristóbal Pérez, Elena Caballero-Mancebo, Francisco J. Basterretxea, Alberto Lesarri, José A. Fernández, Emilio J. Cocinero
      Pages: 7156 - 7156
      Abstract: Invited for the cover of this issue is the group of Emilio J. Cocinero at the University of the Basque Country. The image depicts a fight between two biomolecules, cotinine and nicotine. Read the full text of the article at 10.1002/chem.201700023.“…Cotinine and Nicotine which have to pit their strengths against each other.” Read more about the story behind the cover in the Cover Profile and about the research itself on page 7238 ff. (
      DOI : 10.1002/chem.201700023).
      PubDate: 2017-04-05T02:00:43.670258-05:
       
  • Twisted Amides: From Obscurity to Broadly Useful
           Transition-Metal-Catalyzed Reactions by N−C Amide Bond Activation
    • Authors: Chengwei Liu; Michal Szostak
      Pages: 7157 - 7173
      Abstract: The concept of using amide bond distortion to modulate amidic resonance has been known for more than 75 years. Two classic twisted amides (bridged lactams) ingeniously designed and synthesized by Kirby and Stoltz to feature fully perpendicular amide bonds, and as a consequence emanate amino-ketone-like reactivity, are now routinely recognized in all organic chemistry textbooks. However, only recently the use of amide bond twist (distortion) has advanced to the general organic chemistry mainstream enabling a host of highly attractive N−C amide bond cross-coupling reactions of broad synthetic relevance. In this Minireview, we discuss recent progress in this area and present a detailed overview of the prominent role of amide bond destabilization as a driving force in the development of transition-metal-catalyzed cross-coupling reactions by N−C bond activation.Twist of faith! Recently the use of amide bond twist (distortion) has advanced to the general organic chemistry mainstream enabling a host of highly attractive N−C amide bond cross-coupling reactions of broad synthetic relevance. In this Minireview, recent progress in this area is discussed and a detailed overview of the prominent role of amide bond destabilization as a driving force in the development of transition-metal-catalyzed cross-coupling reactions by N−C amide bond activation is presented.
      PubDate: 2017-02-20T03:30:52.016742-05:
      DOI: 10.1002/chem.201605012
       
  • Double Sequential Encrypted Targeting Sequence: A New Concept for Bone
           Cancer Treatment
    • Authors: Gonzalo Villaverde; Valentina Nairi, Alejandro Baeza, María Vallet-Regí
      Pages: 7174 - 7179
      Abstract: The selective transportation of therapeutic agents to tumoral cells is usually achieved by their conjugation with targeting moieties able to recognize these cells. Unfortunately, simple and static targeting systems usually show a lack in selectivity. Herein, a double sequential encrypted targeting system is proposed as a stimuli-responsive targeting analogue for selectivity enhancement. The system is able to recognize diseased bone tissue in the first place, and once there, a hidden secondary targeting group is activated by the presence of an enzyme overproduced in the malignant tissue (cathepsin K), thereby triggering the recognition of diseased cells. Transporting the cell targeting agent in a hidden conformation that contains a high selective tissular primary targeting, could avoid not only its binding to similar cell receptors but also the apparition of the binding-site barrier effect, which can enhance the penetration of the therapeutic agent within the affected zone. This strategy could be applied not only to conjugate drugs but also to drug-loaded nanocarriers to improve the efficiency for bone cancer treatments.Find the bone and hide: A double sequential encrypted targeting system is presented that is able to recognize bone tissue and afterwards, activated through a cascade process by cathepsin K present in the diseased tissue, will be internalized by osteosarcoma cells.
      PubDate: 2017-03-28T06:40:30.062609-05:
      DOI: 10.1002/chem.201605947
       
  • Formal Synthesis of (+)-Laurencin by Gold(I)-Catalyzed Intramolecular
           Dehydrative Alkoxylation
    • Authors: Megan L. Lanier; Hyeri Park, Paramita Mukherjee, Jacob C. Timmerman, Anthony A. Ribeiro, Ross A. Widenhoefer, Jiyong Hong
      Pages: 7180 - 7184
      Abstract: 8-Membered cyclic ethers are found in a wide range of natural products; however, they are challenging synthetic targets due to enthalpic and entropic barriers. The gold(I)-catalyzed intramolecular dehydrative alkoxylation of ω-hydroxy allylic alcohols was explored to stereoselectively construct α,α′-cis-oxocenes and further applied in a formal synthesis of (+)-laurencin. The gold(I)-catalyzed intramolecular dehydrative alkoxylation may constitute an alternative method for the synthesis of molecular building blocks and natural products that contain highly functionalized 8-membered cyclic ethers.Go for gold! 8-Membered cyclic ethers are challenging synthetic targets found in a wide range of natural products. The gold(I)-catalyzed intramolecular dehydrative alkoxylation of ω-hydroxy allylic alcohols was explored to stereoselectively construct α,α′-cis-oxocenes and further applied in a formal synthesis of (+)-laurencin. The gold(I)-catalyzed intramolecular dehydrative alkoxylation may constitute an alternative method for the synthesis of highly functionalized medium-sized cyclic ethers.
      PubDate: 2017-05-03T04:35:43.804525-05:
      DOI: 10.1002/chem.201700499
       
  • A Ratiometric Near-Infrared Fluorogen for the Real Time Visualization of
           Intracellular Redox Status during Apoptosis
    • Authors: Giridharan Saranya; Palapuravan Anees, Manu M. Joseph, Kaustabh K. Maiti, Ayyappanpillai Ajayaghosh
      Pages: 7191 - 7195
      Abstract: Direct monitoring of apoptotic progression is a major step forward for the early assessment of therapeutic efficacy of certain treatments and the accurate evaluation of the spread of a disease. Here, the regulatory role of glutathione (GSH) is explored as a potential biomarker for tracking apoptosis. For this purpose, a near- infrared (NIR) squaraine dye is introduced that is capable of sensing GSH in a ratiometric manner by switching its emission from NIR (690 nm) to visible region (560 nm). The favorable biocompatible attributes of the probe facilitated the real-time monitoring of apoptotic process in line with the conventional apoptotic assay. Furthermore, the robust nature of the probe was utilized for the quantitative estimation of GSH during different stages of apoptosis. Through this study, an easy and reliable method of assaying apoptosis is demonstrated, which can provide valuable insights in translational clinical research.Status update: A small-molecule-based ratiometric fluorescent probe was designed for the detection of intracellular redox status, which served as a reliable assay for the on-demand real-time probing of glutathione (GSH) fluctuations during apoptosis.
      PubDate: 2017-05-02T10:48:25.649179-05:
      DOI: 10.1002/chem.201700839
       
  • Formation of a Cubic Liquid Crystalline Nanostructure with π-Conjugated
           Fluorinated Rods on the Gyroid Minimal Surface
    • Authors: Marco Poppe; Changlong Chen, Feng Liu, Silvio Poppe, Carsten Tschierske
      Pages: 7196 - 7200
      Abstract: Bicontinuous cubic phases are of significant importance for numerous applications, for example, for the crystallization of membrane proteins, as photonic materials and as templates for porous silica. A new variant of bicontinuous cubic liquid crystalline phase with Ia3‾d lattice is reported herein for X-shaped bolapolyphiles. It was shown that in this class of compounds, cubic-phase induction can be achieved by proper aromatic core fluorination; in addition, the first cubic phases having π-conjugated oligo(phenylene ethynylene) rods on the gyroid minimal surface were obtained. These new structures composed of 3D folded layers of parallel arranged π-conjugated rods should allow charge transport in all three dimensions, which is of interest for organic semiconductor applications.The power of fluorination: Tailoring the fluorination pattern modifies the soft self-assembly of oligo(phenylene ethynylene)-based X-shaped polyphiles, leading to the first thermotropic liquid crystalline cubic phase with the π-conjugated rods forming the gyroid minimal surface. The organization of the rods perpendicular to the minimal surface and parallel to each other allows π-stacking interactions in all three dimensions of space (see figure).
      PubDate: 2017-04-27T19:08:39.608244-05:
      DOI: 10.1002/chem.201700905
       
  • Cytosine–Cytosine Base-Pair Mismatch and Chirality in Nucleotide
           Supramolecular Coordination Complexes
    • Authors: Qi-ming Qiu; Pei Zhou, Leilei Gu, Liang Hao, Minghua Liu, Hui Li
      Pages: 7201 - 7206
      Abstract: The base-pair sequences are the foundation for the biological processes of DNA or RNA, and base-pair mismatch is very important to reveal genetic diseases and DNA rearrangements. However, the lack of well-defined structural information about base-pair mismatch is obstructing the investigation of this issue. The challenge is to crystallize the materials containing the base-pair mismatch. Engineering the small-molecule mimics or model is an effective strategy to solve this issue. Here, six cytidine-5′-monophosphate (CMP) and 2′-deoxycytidine-5′-monophosphate (dCMP) coordination polymers were reported containing cytosine–cytosine base-pair mismatch (i-motif), and their single-crystal structures and chiralities were studied. The precise control over the formation of the i-motif was demonstrated, in which the regulating of supramolecular interactions was achieved based on molecular design. In addition, the chiralities of these coordination polymers were investigated according to their crystal structures and solution- and solid-state circular dichroism spectroscopy.i-motif: A well-defined crystal structure of the i-motif is constructed in the cytidine-5′-monophosphate (CMP) and 2′-deoxycytidine-5′-monophosphate (dCMP) supramolecular coordination polymers, in which the regulating of supramolecular interactions is achieved based on molecular design, and the relative supramolecular chirality is discussed.
      PubDate: 2017-04-24T05:08:24.214474-05:
      DOI: 10.1002/chem.201700930
       
  • Modular Synthesis of Diverse Natural Product-Like Macrocycles: Discovery
           of Hits with Antimycobacterial Activity
    • Authors: Mark Dow; Francesco Marchetti, Katherine A. Abrahams, Luis Vaz, Gurdyal S. Besra, Stuart Warriner, Adam Nelson
      Pages: 7207 - 7211
      Abstract: A modular synthetic approach was developed in which variation of the triplets of building blocks used enabled systematic variation of the macrocyclic scaffolds prepared. The approach was demonstrated in the synthesis of 17 diverse natural product-like macrocyclic scaffolds of varied (12–20-membered) ring size. The biological relevance of the chemical space explored was demonstrated through the discovery of a series of macrocycles with significant antimycobacterial activity.A modular approach enabled the synthesis of 17 diverse natural product-like macrocyclic scaffolds, and the discovery of a distinctive macrocycles with antimycobacterial activity.
      PubDate: 2017-05-02T10:57:03.826453-05:
      DOI: 10.1002/chem.201701150
       
  • Unsymmetrical Iron P-NH-P′ Catalysts for the Asymmetric Pressure
           Hydrogenation of Aryl Ketones
    • Authors: Samantha A. M. Smith; Paraskevi O. Lagaditis, Anne Lüpke, Alan J. Lough, Robert H. Morris
      Pages: 7212 - 7216
      Abstract: The reductive amination of α-dialkylphosphine acetaldehydes with enantiopure β-aminophosphines is a new, versatile route to unsymmetrical tridentate (pincer) ligands P-NH-P′. Four new ligands PR2CH2CH2NHCHR′CHR′′PPh2 (R=iPr, Cy, R′=Ph, CH(CH3)2, R′′=Ph, H) prepared in this way are used to make the iron(II) complexes mer-FeCl2(CO)(P-NH-P′) and mer-FeCl(H)(CO)(P-NH-P′). The hydride complex with the rigid ligand with R′=R′′=Ph is an efficient and highly enantioselective homogeneous asymmetric pressure hydrogenation (APH) catalyst. Prochiral aryl ketones are reduced under mild conditions (THF, 0.1 mol % catalyst, 1 mol % KOtBu, 5–10 bar, 50 °C) to the (S)-alcohols, usually in enantiomeric excess (ee) greater than 90 %. DFT calculations provided transition-state structures for the enantiodetermining hydride-transfer step.(S)inister iron claws: The reductive amination of α-dialkylphosphine acetaldehydes with enantiopure β-aminophosphines is a new, versatile route to unsymmetrical tridentate (pincer) ligands P-NH-P′. Several prochiral aryl ketones are reduced to the (S)-alcohols, usually with ee values greater than 90 %, using 0.1 mol % of an iron complex mer-FeCl(H)(CO)(P-NH-P′) at 5 to 10 bar H2 and 50 °C.
      PubDate: 2017-05-05T06:13:56.036527-05:
      DOI: 10.1002/chem.201701254
       
  • Stable NiII Porphyrin meso-Oxy Radical with a Quartet Ground State
    • Authors: Cosima Stähler; Daiki Shimizu, Kota Yoshida, Ko Furukawa, Rainer Herges, Atsuhiro Osuka
      Pages: 7217 - 7220
      Abstract: 10,15,20-Tris(pentafluorophenyl)-substituted NiII–porphyrin meso-oxy radical bearing two coordinating pyridines was synthesized as a stable radical with a quartet ground state (S=3/2). X-ray structural analysis revealed that the NiII porphyrin moiety is fairly planar and the Ni−N bond lengths are considerably longer, indicating the high-spin state of the NiII center. The radical exhibited a quartet ground state, indicating the ferromagnetic interaction between the high-spin NiII center (S=1) and the porphyrin meso-oxy radical (S=1/2).Hexagonally coordinated NiII complex with 10,15–20-triarylporphyrin meso-oxy radical and two pyridines as ligands was synthesized. The complex exhibited a S=3/2 ground state with large doublet-quartet energy gap due to ferromagnetic interaction between the high-spin NiII center (S=1) and the porphyrin meso-oxy radical (S=1/2). Its structure, as well as optical, magnetic, and electrochemical properties have been fully characterized (see figure).
      PubDate: 2017-05-02T10:52:14.429182-05:
      DOI: 10.1002/chem.201701354
       
  • Fenton-RAFT Polymerization: An “On-Demand” Chain-Growth Method
    • Authors: Amin Reyhani; Thomas G. McKenzie, Hadi Ranji-Burachaloo, Qiang Fu, Greg G. Qiao
      Pages: 7221 - 7226
      Abstract: Fine control over the architecture and/or microstructure of synthetic polymers is fast becoming a reality owing to the development of efficient and versatile polymerization techniques and conjugation reactions. However, the transition of these syntheses to automated, programmable, and high-throughput operating systems is a challenging step needed to translate the vast potential of precision polymers into machine-programmable polymers for biological and functional applications. Chain-growth polymerizations are particularly appealing for their ability to form structurally and chemically well-defined macromolecules through living/controlled polymerization techniques. Even using the latest polymerization technologies, the macromolecular engineering of complex functional materials often requires multi-step syntheses and purification of intermediates, and results in sub-optimal yields. To develop a proof-of-concept of a framework polymerization technique that is readily amenable to automation requires several key characteristics. In this study, a new approach is described that is believed to meet these requirements, thus opening avenues toward automated polymer synthesis.Polymers on demand: A facile technique for the synthesis of controlled polymers is realized by using the Fenton reaction. The ability to degas the reaction mixture by using the same catalyst system and then grow the polymer chain through sequential H2O2 addition is highly promising for the development of an automated/programmable polymerization system utilizing sequenced reagent injection. The benign reaction conditions (room temperature, aqueous solvent) are non-demanding, and the system is demonstrated to be compatible with a range of functional monomers.
      PubDate: 2017-05-03T06:35:48.8576-05:00
      DOI: 10.1002/chem.201701410
       
  • Synthesis, Structures, and Photophysical Properties of Alternating
           Donor–Acceptor Cycloparaphenylenes
    • Authors: Shuhei Nishigaki; Miho Fukui, Haruki Sugiyama, Hidehiro Uekusa, Susumu Kawauchi, Yu Shibata, Ken Tanaka
      Pages: 7227 - 7231
      Abstract: The synthesis of alternating donor–acceptor [12] and [16]cycloparaphenylenes (CPPs) has been achieved by the rhodium-catalyzed intermolecular cross-cyclotrimerization followed by imidation and/or aromatization. These alternating donor–acceptor CPPs showed positive solvatofluorochromic properties and smaller HOMO–LUMO gaps compared with nonfunctionalized CPPs, which was confirmed by the theoretical study.Catherine wheels: The synthesis of alternating donor–acceptor [12] and [16]cycloparaphenylenes (CPPs) has been achieved by the rhodium-catalyzed intermolecular cross-cyclotrimerization followed by imidation and/or aromatization. The alternating donor–acceptor CPPs showed positive solvatofluorochromic properties and smaller HOMO–LUMO gaps compared with nonfunctionalized CPPs, which was confirmed by the theoretical study.
      PubDate: 2017-05-02T10:56:46.078051-05:
      DOI: 10.1002/chem.201701547
       
  • Molecular Assemblies of Metal Complexes via Base-Pairing of Nucleic Acids
           in the Crystalline State
    • Authors: Manabu Nakaya; Ryo Ohtani, Kunihisa Sugimoto, Masaaki Nakamura, Leonard F. Lindoy, Shinya Hayami
      Pages: 7232 - 7237
      Abstract: The nature of the molecular assemblies formed in the crystalline state by cobalt(II) terpyridine (terpy) complexes incorporating appended adenine (A) or thymine (T) bases was found to be controlled by which bases are present. Single-crystals of the cobalt(II) complexes [Co(A-C6-terpy)2](BF4)2 (1) and [Co(T-C6-terpy)2](BF4)2 (2) have needle and block habits, respectively. Subsequent mixing of 1 and 2 in MeOH resulted in isolation of [Co(A-C6-terpy)1.5(T-C6-terpy)0.5](BF4)2 (3) as plate-like crystals. A 3D network structure is present in 1 that incorporates 1D chains, whereas 2 adopts a 2D stacked structure constructed from ladder-type assemblies. For 3, “dimer-rings” consisting of [Co(A-C6-terpy)2]2+ and [Co(A-C6-terpy)(T-C6-terpy)]2+ units are generated by means of base-pairing between A and T. Notably, 3 displays the first crystal structure of a heteroleptic cobalt(II) complex of [Co(A-C6-terpy)(T-C6-terpy)](BF4)2. These assembly differences involving the terpyridine cobalt(II) complex units in 1–3 affect the cooperativities influencing their spin crossover (SCO) behavior. The influence of the terminal nucleobases on the resulting assembly has been probed by investigating the co-crystallization of [Co(terpy)2](BF4)2 (4) with [Co(C6-terpy)2](BF4)2 (5) and 1 with 5.Complex Cobalt Crystals! Molecular assemblies of the nucleobase-appended cobalt(II) complexes [Co(A-C6-terpy)2](BF4)2 (1) and [Co(T-C6-terpy)2](BF4)2 (2) have been investigated. Subsequent mixing of 1 and 2 in MeOH resulted in isolation of [Co(A-C6-terpy)1.5(T-C6-terpy)0.5](BF4)2 (3), which is the first crystal structure of a heteroleptic cobalt(II) complex of [Co(A-C6-terpy)(T-C6-terpy)](BF4)2.
      PubDate: 2017-04-10T08:11:21.801469-05:
      DOI: 10.1002/chem.201700593
       
  • Structural Studies of Nicotinoids: Cotinine versus Nicotine
    • Authors: Iciar Uriarte; Cristóbal Pérez, Elena Caballero-Mancebo, Francisco J. Basterretxea, Alberto Lesarri, José A. Fernández, Emilio J. Cocinero
      Pages: 7238 - 7244
      Abstract: Nicotinoids are agonists of the acetylcholine receptor (nAChR) and play important biochemical and pharmacological roles. Herein, we report on the structure and conformation of cotinine, and compare its molecular properties with the nicotine prototype, from which it only differs in the addition of a carbonyl group. This investigation included a theoretical survey of the effects of rotamerization of the pyridine moiety, the puckering of the pyrrolidinone ring and the internal rotation of the methyl group. The experimental work examined the rotational spectrum of the molecule in a supersonic expansion, using both broadband chirped-pulse excitation techniques and cavity microwave spectrometers. Two conformers were observed for cotinine, and the fine and hyperfine structures arising from the two quadrupolar 14N nuclei and the methyl internal rotor were fully analyzed. The two observed conformers share the same twisted conformation of the five-membered ring, but differ in a roughly 180° rotamerization around the C−C bond connecting the two rings. The energy barriers for the internal rotation of the methyl group in cotinine (4.55(4) and 4.64(3) kJ mol−1, respectively) are much lower than in nicotine (estimated in 16.5 kJ mol−1). The combination of different intramolecular electronic effects, hydrogen bonding and possible binding differences to receptor molecules arising from the carbonyl group could explain the lower affinity of cotinine for nAChRs.Through the smoke: The conformation of cotinine was probed under isolation conditions by microwave spectroscopy. Interesting results are revealed when compared to structurally related nicotine in terms of the ring conformation, internal methyl rotation, and intramolecular interactions.
      PubDate: 2017-03-27T04:31:33.484422-05:
      DOI: 10.1002/chem.201700023
       
  • Formation of δ-Lactones with anti-Baeyer–Villiger Regiochemistry:
           Investigations into the Mechanism of the Cerium-Catalyzed Aerobic Coupling
           of β-Oxoesters with Enol Acetates
    • Authors: Irina Geibel; Anna Dierks, Thomas Müller, Jens Christoffers
      Pages: 7245 - 7254
      Abstract: The cerium-catalyzed, aerobic coupling of β-oxoesters with enol acetates and dioxygen yields δ-lactones with a 1,4-diketone moiety. In contrast to the Baeyer–Villiger oxidation (BVO), where the higher substituted residue migrates; in the case of this oxidative C−C coupling reaction, the less substituted alkyl residue undergoes a 1,2-shift. An endoperoxidic oxycarbenium ion comparable to the Criegee intermediate in the BVO is proposed as a reaction intermediate and submitted to conformational analysis by computational methods. As a result, the inverse regiochemistry is explained by a primary stereoelectronic effect. A Hammett analysis using different donor- and acceptor-substituted enol esters provides support for the oxycarbenium ion being the crucial intermediate in the rate determining step of the conversion. An overall mechanism is suggested with a radical chain reaction for the formation of endoperoxides from β-oxoesters, enol acetates and dioxygen with a cerium(IV) species as initiating reagent.Cer-tified mechanism: Reaction kinetics (Hammett analysis) supported by computational methods indicate an endoperoxidic oxycarbenium ion to be the reaction intermediate for the cerium-catalyzed coupling of β-oxoesters, enol acetates and dioxygen.
      PubDate: 2017-03-30T06:00:58.13869-05:0
      DOI: 10.1002/chem.201605468
       
  • Design of Na+-Selective Fluorescent Probes: A Systematic Study of the
           Na+-Complex Stability and the Na+/K+ Selectivity in Acetonitrile and Water
           
    • Authors: Thomas Schwarze; Holger Müller, Darya Schmidt, Janine Riemer, Hans-Jürgen Holdt
      Pages: 7255 - 7263
      Abstract: There is a tremendous demand for highly Na+-selective fluoroionophores to monitor the top analyte Na+ in life science. Here, we report a systematic route to develop highly Na+/K+ selective fluorescent probes. Thus, we synthesized a set of fluoroionophores 1, 3, 4, 5, 8 and 9 (see Scheme ) to investigate the Na+/K+ selectivity and Na+- complex stability in CH3CN and H2O. These Na+-probes bear different 15-crown-5 moieties to bind Na+ stronger than K+. In the set of the diethylaminocoumarin-substituted fluoroionophores 1–5, the following trend of fluorescence quenching 1>3>2>4>5 in CH3CN was observed. Therefore, the flexibility of the aza-15-crown-5 moieties in 1–4 determines the conjugation of the nitrogen lone pair with the aromatic ring. As a consequence, 1 showed in CH3CN the highest Na+-induced fluorescence enhancement (FE) by a factor of 46.5 and a weaker K+ induced FE of 3.7. The Na+-complex stability of 1–4 in CH3CN is enhanced in the following order of 2>4>3>1, assuming that the O-atom of the methoxy group in the ortho-position, as shown in 2, strengthened the Na+-complex formation. Furthermore, we found for the N-(o-methoxyphenyl)aza-15-crown-5 substituted fluoroionophores 2, 8 and 9 in H2O, an enhanced Na+-complex stability in the following order 8>2>9 and an increased Na+/K+ selectivity in the reverse order 9>2>8. Notably, the Na+-induced FE of 8 (FEF=10.9), 2 (FEF=5.0) and 9 (FEF=2.0) showed a similar trend associated with a decreased K+-induced FE [8 (FEF=2.7)>2 (FEF=1.5)>9 (FEF=1.1)]. Here, the Na+-complex stability and Na+/K+ selectivity is also influenced by the fluorophore moiety. Thus, fluorescent probe 8 (Kd=48 mm) allows high-contrast, sensitive, and selective Na+ measurements over extracellular K+ levels. A higher Na+/K+ selectivity showed fluorescent probe 9, but also a higher Kd value of 223 mm. Therefore, 9 is a suitable tool to measure Na+ concentrations up to 300 mm at a fluorescence emission of 614 nm.Probing for ions: We report on the development of Na+-selective fluorescent probes, which consist of 15-membered crown ether ionophores and of coumarin or π-extended coumarin derivatives, as fluorophores. These fluoroionophores show different Na+-complex stabilities and Na+/K+ selectivities in acetonitrile and water.
      PubDate: 2017-04-04T02:45:46.512638-05:
      DOI: 10.1002/chem.201605986
       
  • N-Doped Mesoporous In2O3 for Photocatalytic Oxygen Evolution from the
           In-based Metal–Organic Frameworks
    • Authors: Xiaoyu Gan; Ruijin Zheng, Tianlin Liu, Jiao Meng, Ruiping Chen, Xuan Sun, Xun Sun
      Pages: 7264 - 7271
      Abstract: As an excellent n-type semiconductor, indium oxide (In2O3) is also a good candidate for photocatalysis such as light-induced water splitting. However, the efficiency of the oxygen evolution reaction (OER) underperforms in view of the wide band gap (BG) and fast charge recombination in In2O3. N-doping provides a sound method to narrow the BG and to prohibit the charge recombination by forming new energy levels between the valence band (VB) and the conduction band (CB). In this work, an In-based organic framework sod-ZMOF was used as a precursor to prepare the N-doped In2O3. After calcination, sod-ZMOF is transformed into N-doped In2O3 nanocrystalline, in which the ligand within sod-ZMOF serves as the nitrogen source. In addition, sod-ZMOF acts as self-template during calcination to generate abundant nanopores within the In2O3 frameworks, providing large specific surface area and active sites for OER. The BG is narrowed to 2.9 from 3.7 eV of the pure In2O3 on account of the N-doping. N species are doped in both the substitutional and interstitial fashion, and the interstitial doping is believed to improve the photo-induced carrier separation by the formation of oxygen vacancies. As a consequence, the overpotential for OER is effectively decreased from the pure In2O3, and the electrocatalytic experiment proves superior catalytic activity with a high current density and long-term durability compared to the In2O3 nanoparticles obtained from In(OH)3.Superior photocatalytic OER performance: a facile and effective method to construct an N-doped structure from the corresponding metal–organic framework (MOF) precursor, which provides superior photocatalytic oxygen evolution reaction (OER) performance with large specific surface area and multilevel porosity, narrowed energy band, as well as stabilized photoinduced charge separation.
      PubDate: 2017-03-30T01:07:19.060667-05:
      DOI: 10.1002/chem.201605576
       
  • Platinum-Based Organometallic Folders for the Recognition of
           Electron-Deficient Aromatic Substrates
    • Authors: Daniel Nuevo; Sergio Gonell, Macarena Poyatos, Eduardo Peris
      Pages: 7272 - 7277
      Abstract: A series of platinum complexes with cis-oriented polyaromatic N-heterocyclic carbene ligands were prepared and characterized. The relative disposition of the polyaromatic ligands about the metal cause these compounds to behave as metallofolders, featuring a cavity defined by the void space between the polyaromatic functionalities. The complexes were used as receptors of organic molecules, whereby selective affinity was displayed for electron-deficient aromatic substrates, such as 1,2,4,5-tetracyanobenzene (TCNB), 2,4,7-trinitro-9-fluorenone (TNFLU), and 1,4,5,8-naphtalenetetracarboxylic dianhydride (NTCDA). The binding affinities of two of the metallofolders with these substrates were determined by means of 1H NMR titrations. Electrospray mass spectrometry (ESI-MS) was also used to assess the affinities. The molecular structure of one of the platinum folders was determined in the presence of TCNB, showing the clear interaction between this guest molecule and the folder formed by the two mutually cis-oriented polyaromatic ligands. This work demonstrates how the presence of the mutually cis-oriented polyaromatic ligands may be a very useful tool for the preparation of metal-based receptors.Chemical office: A series of platinum complexes with cis-oriented polyaromatic N-heterocyclic carbene ligands behave as metallofolders, and can be used as receptors for electron-deficient aromatic substrates.
      PubDate: 2017-05-10T02:05:28.750964-05:
      DOI: 10.1002/chem.201605241
       
  • Photoluminescent Honeycomb Structures from Polyoxometalates and an
           Imidazolium-Based Ionic Liquid Bearing a π-Conjugated Moiety and a
           Branched Aliphatic Chain
    • Authors: Geping Zhang; Hongxia Zhu, Mengjun Chen, Hongguang Li, Ye Yuan, Tiantai Ma, Jingcheng Hao
      Pages: 7278 - 7286
      Abstract: Honeycomb-structured films represent an intriguing class of two-dimensional porous materials. Specifically, polyoxometalate (POM) macroanions can be introduced into these films by complexing with oppositely charged, double-tailed surfactants. Here highly-ordered honeycomb structures are reported that can be constructed by the complexes between POMs and a room temperature ionic liquid (IL1) having an imidazolium moiety in the middle and a naphthyl unit and a branched aliphatic chain at the ends. The complexes can be produced through phase transfer between an aqueous solution of POMs (typically {Mo72Fe30}) and a CS2 (or chloroform) solution of IL1. Based on the intrinsic properties of {Mo72Fe30} and the functional groups of the IL1, the honeycomb structures show multiple functions with bright photoluminescence and rich electrochemical properties. This work shows that by simply engineering the organic ligands involved in the POM-based inorganic–organic complexes, supramolecular structures with improved properties and wide applications can be obtained.Honey trap: Highly-ordered, photoluminescent honeycomb structures with rich electrochemical properties have been fabricated by complexing {Mo72Fe30} and a room-temperature ionic liquid which bears naphthyl unit and a long, branched aliphatic chain.
      PubDate: 2017-05-08T04:54:47.282452-05:
      DOI: 10.1002/chem.201605651
       
  • Peroxotantalate-Based Ionic Liquid Catalyzed Epoxidation of Allylic
           Alcohols with Hydrogen Peroxide
    • Authors: Wenbao Ma; Chen Chen, Kang Kong, Qifeng Dong, Kun Li, Mingming Yuan, Difan Li, Zhenshan Hou
      Pages: 7287 - 7296
      Abstract: The efficient and environmentally benign epoxidation of allylic alcohols has been attained by using new kinds of monomeric peroxotantalate anion-functionalized ionic liquids (ILs=[P4,4,4,n]3[Ta(O)3(η-O2)], P4,4,4,n=quaternary phosphonium cation, n=4, 8, and 14), which have been developed and their structures determined accordingly. This work revealed the parent anions of the ILs underwent structural transformation in the presence of H2O2. The formed active species exhibited excellent catalytic activity, with a turnover frequency for [P4,4,4,4]3[Ta(O)3(η-O2)] of up to 285 h−1, and satisfactory recyclability in the epoxidation of various allylic alcohols under very mild conditions by using only one equivalent of hydrogen peroxide as an oxidant. NMR studies showed the reaction was facilitated through a hydrogen-bonding mechanism, in which the peroxo group (O–O) of the peroxotantalate anion served as the hydrogen-bond acceptor and hydroxyl group in the allylic alcohols served as the hydrogen-bond donor. This work demonstrates that simple monomeric peroxotantalates can catalyze epoxidation of allylic alcohols efficiently.IL at ease: Novel ionic liquids (ILs) consisting of quaternary phosphonium cations and a monomeric peroxotantalate anion have been prepared and their structures were determined accordingly. The ILs exhibited highly catalytic performance for the epoxidation of allylic alcohols under solvent-free and ice bath conditions. The parent anions of the ILs underwent structural changes after reaction with H2O2 and a hydrogen-bond interaction between the peroxotantalate anion and hydroxyl group of allylic alcohols is proposed.
      PubDate: 2017-05-10T06:41:02.935901-05:
      DOI: 10.1002/chem.201605661
       
  • Robust MOFs of “tsg” Topology Based on Trigonal Prismatic Organic and
           Metal Cluster SBUs: Single Crystal to Single Crystal Postsynthetic Metal
           Exchange and Selective CO2 Capture
    • Authors: Pujari Chandrasekhar; Govardhan Savitha, Jarugu Narasimha Moorthy
      Pages: 7297 - 7305
      Abstract: The self-assembly of a rigid and trigonal prismatic triptycene-hexaacid H6THA with Co(NO3)2 or Mn(NO3)2 leads to isostructural metal-organic frameworks (MOFs) that are sustained by 6-connecting metal cluster [M3(μ3-O)(COO)6] secondary building units (SBUs). The Co- and Mn-MOFs, constructed from organic and metal-cluster building blocks that are both trigonal prismatic, correspond to the heretofore unknown “tsg” topology. Due to the rigidity and concave attributes of H6THA, the networks in the Co- and Mn-MOFs are highly porous and undergo 3-fold interpenetration. The interpenetration imparts permanent microporosity and high thermal stability to the MOFs to permit postsynthetic metal exchange (PSME) and gas sorption. The PSME occurs in a single crystal to single crystal fashion when the crystals of Co- or Mn-MOFs are immersed in a solution of Cu(NO3)2 in MeOH/H2O. Further, the isostructural robust MOFs exhibit significant gas sorption and remarkable selectivity for CO2 over N2 (ca. 100 fold) at ambient conditions. In fact, the postsynthetically-engineered Cu-THA exhibits better CO2 sorption than Co-THA and Mn-THA. A composite of effects that include pore dimensions (ca. 0.7 nm), unsaturated metal centers, and basic environments conferred by the quinoxaline nitrogen atoms appears to be responsible for the observed high CO2 capture and selectivity. The high symmetry and structural attributes of the organic linker seemingly dictate adoption of the trigonal-prismatic metal cluster SBU by the metal ions in the MOFs.3 and 3 are Stronger Together: Metal-mediated self-assembly of triptycene-hexaacid H6THA, which typifies a trigonal prismatic 6-connecting linker built up by joining two 3-connecting trigonal linkers together, leads to robust MOFs sustained by trigonal prismatic SBUs. The MOFs exhibit significant CO2 adsorption capacities with a high selectivity for CO2 over N2.
      PubDate: 2017-05-08T05:13:12.619365-05:
      DOI: 10.1002/chem.201700139
       
  • Tuning Hole and Electron Transfer from Photoexcited CdSe Quantum Dots to
           
    • Authors: Tushar Debnath; Deepa Sebastian, Sourav Maiti, Hirendra N. Ghosh
      Pages: 7306 - 7314
      Abstract: Charge-transfer processes from photoexcited CdSe quantum dots (QDs) to phenol derivatives with electron- donating (4-methoxy) and -withdrawing (4-nitro) moieties have been demonstrated by using steady-state and time- resolved emission and femtosecond transient absorption spectroscopy. Steady-state and time-resolved emission studies suggest that in the presence of both 4-nitrophenol (4NP) and 4-methoxyphenol (4MP) CdSe QDs luminescence is quenched. Stern–Volmer analysis suggests both static and dynamic mechanisms are active for both the QD/phenol composites. Cyclic voltammetric analysis recommends that photoexcited CdSe QDs can donate electrons to 4NP and holes to 4MP. To reconfirm both electron- and hole-transfer mechanisms, CdSe/CdS quasi-type II and CdSe/CdTe type II core–shell nanocrystals were synthesized and photoluminescence quenching was monitored in the absence and presence of both 4NP and 4MP, for which hole and electron transfer were systematically restricted. Results suggest that indeed electron and hole transfer take place from photoexcited CdSe to 4NP and 4MP, respectively. To monitor the charge-transfer dynamics in both systems on an early timescale, femtosecond transient absorption spectroscopic techniques have been employed. Electron and hole transfer and charge-recombination dynamics are discussed and the effect of electron-donating and -withdrawing groups has been demonstrated.A sense of direction: Electron-withdrawing 4-nitrophenol (4-NP) act as an electron quencher, whereas electron-donating 4-methoxyphenol (4-MP) acts as a hole quencher in CdSe nanocrystals (see figure). Thus, by varying the substituent in phenol, favorable energy-level alignment results in changes to the quenching behavior.
      PubDate: 2017-05-10T02:05:38.738178-05:
      DOI: 10.1002/chem.201700166
       
  • Supramolecular Covalence in Bifurcated Chalcogen Bonding
    • Authors: Pankaj Lochan Bora; Martin Novák, Jan Novotný, Cina Foroutan-Nejad, Radek Marek
      Pages: 7315 - 7323
      Abstract: Supramolecular interactions are generally classified as noncovalent. However, recent studies have demonstrated that many of these interactions are stabilized by a significant covalent component. Herein, for systems of the general structure [MX6]2−:YX2 (M=Se or Pt; Y=S, Se, or Te; X=F, Cl, Br, I), featuring bifurcated chalcogen bonding, it is shown that, although electrostatic parameters are useful for estimating the long-range electrostatic component of the interaction, they fail to predict the correct order of binding energies in a series of compounds. Instead, the Lewis basicity of the individual substituents X on the chalcogen atom governs the trends in the binding energies through fine-tuning the covalent character of the chalcogen bond. The effects of substituents on the binding energy and supramolecular electron sharing are consistently identified by an arsenal of theoretical methods, ranging from approaches based on the quantum chemical topology to analytical tools based on the localized molecular orbitals. The chalcogen bonding investigated herein is driven by orbital interactions with significant electron sharing; this can be designated as supramolecular covalence.Let's share! Supramolecular covalence, quantified by orbital interactions and interatomic electron sharing, is demonstrated to dominate the chalcogen-bond interaction. Electrostatic potentials fail to predict the trends in binding energies (see figure).
      PubDate: 2017-04-26T06:42:38.177515-05:
      DOI: 10.1002/chem.201700179
       
  • On the Fine-Tuning of the Excited-State Intramolecular Proton Transfer
           (ESIPT) Process in 2-(2′-Hydroxybenzofuran)benzazole (HBBX) Dyes
    • Authors: Elodie Heyer; Karima Benelhadj, Simon Budzák, Denis Jacquemin, Julien Massue, Gilles Ulrich
      Pages: 7324 - 7336
      Abstract: Herein, a full investigation of the optical properties and first-principles calculations of a large series of original 2-(2′-hydroxybenzofuran)benzazole (HBBX) dyes is described. The electronic substitution on the π-conjugated core of the fluorophores and the nature of the heteroatom (O, S, N) was varied extensively to assess the necessary parameters to trigger a partial frustration of the excited-state intramolecular proton transfer (ESIPT) process, which results in the emission of both tautomers, that is, enol and keto (E* and K*). The optical properties, studied in solution and in the solid state, revealed the appearance of either an intense single K* or a dual E*/K* emission; a feature that is highly dependent on the electronic substitution (donating or accepting), the heteroelement, and the close environment. Subtle modifications of these parameters allowed the establishment of structure–property relationships that were successfully rationalized by first-principles calculations. In particular, the E*/K* emission intensity ratio was shown to be directly related to the free energies of the two emissive tautomers in the excited state.A study of frustration: A series of 2-(2′-hydroxybenzofuran)benzazole (HBBX) dyes has been prepared and studied. Their optical properties were shown to be highly dependent on the substitution and the close environment (see figure; EA=electron acceptor, ED=electron donor). These observations were rationalized by using first-principles calculations.
      PubDate: 2017-05-10T02:25:42.899124-05:
      DOI: 10.1002/chem.201700299
       
  • Synthesis and Characterisation of Chiral Triazole-Based Halogen-Bond
           Donors: Halogen Bonds in the Solid State and in Solution
    • Authors: Mikk Kaasik; Sandra Kaabel, Kadri Kriis, Ivar Järving, Riina Aav, Kari Rissanen, Tõnis Kanger
      Pages: 7337 - 7344
      Abstract: A general platform for the synthesis of various chiral halogen-bond (XB) donors based on the triazole core and the characterisation of factors that influence the strength of the halogen bond in the solid state and in solution are reported. The characterisation of XB donors in the solid state by X-ray crystallography and in solution by 1H NMR titration can be used to aid the design of new XB donors. We describe the first example of a XB between iodotriazoles and thioureas in solution. In addition, the enantiodiscrimination of acceptors in solution through halogen-bond participation is described.Halogen bonds explained: A general platform for the synthesis of various chiral halogen-bond donors based on the triazole core (see figure) and the characterisation of factors that influence the strength of the halogen bond in the solid state and in solution are reported. The enantiodiscrimination of acceptors through halogen-bond participation is described.
      PubDate: 2017-05-10T02:30:44.299365-05:
      DOI: 10.1002/chem.201700618
       
  • Induced Rate Performance Enhancement in Off-Stoichiometric
           Na3+3xV2−x(PO4)3 with Potential Applicability as the Cathode for
           Sodium-Ion Batteries
    • Authors: María J. Aragón; Pedro Lavela, Gregorio F. Ortiz, Ricardo Alcántara, José L. Tirado
      Pages: 7345 - 7352
      Abstract: Off-stoichiometric Na3+3xV2−x(PO4)3 samples have been prepared by a sol-gel route. X-ray diffraction and XPS revealed the flexibility of the NASICON framework to accommodate these deviations of the stoichiometry; at least for low x values. X-ray photoelectron spectra evidenced the presence of Na4P2O7 impurities. The synergic combination of the structural deviations and the presence of Na4P2O7 impurities induce a significant improvement of the electrochemical performance and cycling stability at high rates, as compared to the stoichiometric Na3V2(PO4)3 sample. The fast kinetic response provided by the induced off-stoichiometry involves a decrease of the cell resistance.Useful impurities: The synergic combination of the structural deviations and the presence of the amorphous pyrophosphate impurity in off-stoichiometric Na3+3xV2−x(PO4)3/C induce a significant improvement of the electrochemical performance as positive electrode for Na-ion batteries.
      PubDate: 2017-05-08T06:20:40.044645-05:
      DOI: 10.1002/chem.201700716
       
  • Potassium Nitraminofurazan Derivatives: Potential Green Primary Explosives
           with High Energy and Comparable Low Friction Sensitivities
    • Authors: Ying Li; Haifeng Huang, Yameng Shi, Jun Yang, Renming Pan, Xiangyang Lin
      Pages: 7353 - 7360
      Abstract: Lead-based primary explosives were widely applied in military and civilian ammunition, which have subsequently caused serious environmental and health-related problems. Therefore, the development of green alternatives for the lead-based primary explosives has been one of the major focuses in the field of energetic materials. Four potassium salts based on nitraminofurazan have been easily synthesized and show excellent comprehensive performances. Among them, potassium 3-dinitromethyl-4-nitraminofurazan (K2DNMNAF, 1) showed better thermal stability (Td: 281.4 °C), higher density (2.174 g cm−3), and lower friction sensitivities (72 N) than that of potassium 4,5-bis(dinitromethyl)furoxanate (K2BDNMF, Td: 218.3 °C, density: 2.130 g cm−3, FS: 5 N, P: 27.3 GPa, vD: 7759 m s−1); furthermore, it displayed comparable detonation performances (P: 27.2 GPa, vD: 7758 m s−1). The promising properties of these salts make this kind of material a competitive alternative to lead azide as a primary explosive.An alternative for lead azide: Four potassium salts based on nitraminofurazan are easily synthesized and show excellent comprehensive performances as primary explosives. Among them, potassium 3-dinitromethyl-4-nitraminofurazan (K2DNMNAF, 1) exhibited promising detonation performances, good thermal stability, and comparably low friction sensitivity, which make it a competitive, green alternative to lead-based primary explosives (see scheme).
      PubDate: 2017-05-05T06:19:18.486069-05:
      DOI: 10.1002/chem.201700739
       
  • Self-Exfoliated Metal-Organic Nanosheets through Hydrolytic Unfolding of
           Metal-Organic Polyhedra
    • Authors: Bikash Garai; Arijit Mallick, Anuja Das, Rabibrata Mukherjee, Rahul Banerjee
      Pages: 7361 - 7366
      Abstract: Few-layers thick metal-organic nanosheets have been synthesized using water-assisted solid-state transformation through a combined top-down and bottom-up approach. The metal-organic polyhedra (MOPs) convert into metal-organic frameworks (MOFs) which subsequently self-exfoliate into few-layered metal-organic nanosheets. These MOP crystals experience a hydrophobicity gradient with the inner surface during contact with water because of the existence of hydrophobic spikes on their outer surface. When the amount of water available for interaction is higher, the resultant layers are not stacked to form bulk materials; instead few-layered nanosheets with high uniformity were obtained in high yield. The phenomenon has resulted high yield production of uniformly distributed layered metal-organic nanosheets from three different MOPs, showing its general adaptability.Two-dimensional metal organic nanosheets with few nanometers thickness have been synthesized through a unique combination of top-down and bottom-up approaches using water-assisted self-exfoliation of metal-organic polyhedra.
      PubDate: 2017-05-08T06:15:59.291181-05:
      DOI: 10.1002/chem.201700848
       
  • Di-Zinc–Aryl Complexes: CO2 Insertions and Applications in
           Polymerisation Catalysis
    • Authors: Charles Romain; Jennifer A. Garden, Gemma Trott, Antoine Buchard, Andrew J. P. White, Charlotte K. Williams
      Pages: 7367 - 7376
      Abstract: Two new di-zinc–aryl complexes, [LZn2Ph2] and [LZn2(C6F5)2], coordinated by a diphenol tetraamine macrocyclic ligand have been prepared and fully characterised, including by single-crystal X-ray diffraction experiments. The complexes’ reactivities with monomers including carbon dioxide, cyclohexene oxide, phthalic anhydride, isopropanol and phenol were investigated using both experimental studies and density functional theory calculations. In particular, [LZn2Ph2] readily inserts carbon dioxide to form a carboxylate, at 1 bar pressure, whereas [LZn2(C6F5)2] does not react. Under these conditions [LZn2Ph2] shows moderate activity in the ring-opening copolymerisation of cyclohexene oxide/carbon dioxide (TOF=20 h−1), cyclohexene oxide/phthalic anhydride (TOF=33 h−1) and the ring-opening polymerisations of rac-lactide (TOF=99 h−1) and ϵ-caprolactone (TOF=5280 h−1).Versatile catalysis: Reactivity studies of zinc–aryl complexes towards carbon dioxide, alcohols, epoxides and anhydrides are investigated using a combination of experimental methods and density functional theory calculations. The catalyst systems are active for both ring-opening copolymerisation of epoxide with CO2 or anhydrides, and the ring-opening polymerisation of lactones.
      PubDate: 2017-05-05T06:19:26.313693-05:
      DOI: 10.1002/chem.201701013
       
  • Inside Back Cover: Design of Na+-Selective Fluorescent Probes: A
           Systematic Study of the Na+-Complex Stability and the Na+/K+ Selectivity
           in Acetonitrile and Water (Chem. Eur. J. 30/2017)
    • Authors: Thomas Schwarze; Holger Müller, Darya Schmidt, Janine Riemer, Hans-Jürgen Holdt
      Pages: 7377 - 7377
      Abstract: Na+ is one of the top analytes in the life sciences. Therefore, the development of easily accessible and highly Na+ selective fluorescent tools to monitor extra- or intracellular Na+ levels by fluorescence enhancement is still a challenge. Here, we report easily synthesizable fluorescent probes for Na+ made by “click” chemistry. These fluorescent probes show tunable fluorescence emission wavelengths, dissociation constants, and different Na+/K+ selectivities in CH3CN and H2O. More information can be found in the Full Paper by H.-J. Holdt et al. on page 7255.
      PubDate: 2017-03-22T07:47:49.939842-05:
      DOI: 10.1002/chem.201701038
       
  • Back Cover: N-Doped Mesoporous In2O3 for Photocatalytic Oxygen Evolution
           from the In-based Metal–Organic Frameworks (Chem. Eur. J. 30/2017)
    • Authors: Xiaoyu Gan; Ruijin Zheng, Tianlin Liu, Jiao Meng, Ruiping Chen, Xuan Sun, Xun Sun
      Pages: 7378 - 7378
      Abstract: N-doped In2O3 was obtained from the corresponding metal-organic-framework (MOF) precursor, and demonstrated remarkable performance in photocatalytic water splitting. N-doping endows the catalyst with a narrowed energy band and stabilized photo-induced charge separation. Large specific surface area and multilevel porosity are derived from the porous structure of the In-MOF. These features distinctly enhance the photocatalytic reactivity. More information can be found in the Full Paper by X. Sun, X. Sun et al. on page 7264.
      PubDate: 2017-03-30T01:07:55.922067-05:
      DOI: 10.1002/chem.201701241
       
 
 
JournalTOCs
School of Mathematical and Computer Sciences
Heriot-Watt University
Edinburgh, EH14 4AS, UK
Email: journaltocs@hw.ac.uk
Tel: +00 44 (0)131 4513762
Fax: +00 44 (0)131 4513327
 
Home (Search)
Subjects A-Z
Publishers A-Z
Customise
APIs
Your IP address: 54.146.5.196
 
About JournalTOCs
API
Help
News (blog, publications)
JournalTOCs on Twitter   JournalTOCs on Facebook

JournalTOCs © 2009-2016