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Journal Cover Chemistry - A European Journal
  [SJR: 2.323]   [H-I: 188]   [162 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  [1597 journals]
  • Sulfones as Synthetic Linchpins: Transition Metal-Free sp3-sp2 and sp2-sp2
    • Authors: Barry M. Trost; Chris Kalnmals
      Abstract: Herein, we report a valuable umpolung strategy that highlights the ambiphilic nature of the bis(phenylsulfonyl)methyl synthon and demonstrates its utility as a synthetic linchpin. While the bis(phenylsulfonyl)methyl group is typically introduced as an sp3 carbon nucleophile, we demonstrate that it can also function as an effective sp2 carbon electrophile in the presence of organolithium nucleophiles. Akyl- and aryllithiums couple with the central carbon of the bis(phenylsulfonyl)methyl unit to ultimately generate trisubstituted alkenes, comprising a formal sp3-sp2 and sp2-sp2 cross-coupling between organolithiums and bis(sulfones). This process occurs almost instantaneously at -78 °C in the absence of any transition metals. By developing this curious transformation, we demonstrate that bis(phenylsulfonyl)methane is a valuable synthetic linchpin that can undergo two C-C bond formations as an sp3 nucleophile, followed by a third C-C bond forming reaction as an effective sp2 electrophile. This discovery significantly enhances the utility of this ubiquitous - but underutilized - linker group.
      PubDate: 2018-03-15T15:25:48.581891-05:
      DOI: 10.1002/chem.201800118
  • Harnessing Biology to Deliver Therapeutic and Imaging Entities via
           Cell-Based Methods
    • Authors: Bishnu P. Joshi; Joseph Hardie, Michelle E Farkas
      Abstract: The accumulation of therapeutic and imaging agents at sites of interest is critical to their efficacy. Similarly, off-target effects (especially toxicity) are a major liability for these agents. For this reason, the use of delivery vehicles to improve the distribution characteristics of bio-active agents has become ubiquitous in the field. However, the majority of traditionally employed, cargo-bearing entities rely on passive accumulation. Even in cases where 'targeting' functionalities are used, the agents must first reach the site in order for the ligand-receptor interaction to occur. The next stage of vehicle development is the use of 'recruited' entities, which respond to biological signals produced in the tissues to be targeted, resulting in improved specificities. Recently, many advances have been made in the utilization of cells as delivery agents. They are biocompatible, exhibit excellent circulation lifetimes and tissue penetration capabilities, and respond to chemotactic signals. In this mini-review, we will explore various cell types, modifications, and applications where cell-based delivery agents are used.
      PubDate: 2018-03-15T11:56:39.427758-05:
      DOI: 10.1002/chem.201706180
  • From Monodisperse Thienyl- and Furylborane Oligomers to Polymers -
           Modulating the Optical Properties Through the Hetarene Ratio
    • Authors: Artur Lik; Sangeth Jenthra, Lars Fritze, Lars Müller, Khai-Nghi Truong, Holger Helten
      Abstract: The application of our newly developed B-C coupling method by catalytic Si/B exchange is demonstrated for the synthesis of a series of triarylboranes (1), monodisperse thienyl- and furylborane dimers (2) and trimers (9), extended oligomers (3) and polymers (3'), as well as mixed (oligo)thienyl-/furylboranes. The structures of 1aaTip, 1bbTip, and 2bbbMes*, determined by X-ray crystallography, reveal largely coplanar hetarene rings and BR3 environments, being most pronounced in the furylborane species. Photophysical investigations, supported by TD-DFT calculations, revealed pronounced pi-electron delocalization over the hetarene backbones including the boron centers. Having extended series of derivatives of varying chain lengths available, allowed us to determine the effective conjugation lengths (ECL) of poly(thienylborane)s and poly(furylborane)s, which have been reached with the highest-molecular-weight derivatives of our study. Through variation of the furan-to-thiophene ratio, the photophysical properties of these materials are effectively modulated. Significantly, higher furan contents lead to considerably increased fluorescence intensities. Compounds 1aaTip, 1bbTip, and 3aTip showed the ability to bind fluoride anions. The binding process is signaled by a distinct change in their optical absorption characteristics, thus rendering these materials attractive targets for sensory applications.
      PubDate: 2018-03-15T10:06:34.029596-05:
      DOI: 10.1002/chem.201706124
  • Detection and imaging of Aβ1-42 and Tau fibrils by redesigned
           fluorescent X-34 analogues
    • Authors: Jun Zhang; Alexander Sandberg, Audun Konsmo, Xiongyu Wu, Sofie Nyström, K. Peter Nilsson, Peter Konradsson, Harry LeVine, Mikael Lindgren, Per Hammarström
      Abstract: We revisited the Congo red analogue 2,5-bis(4'-hydroxy-3'-carboxy-styryl)benzene (X-34) to develop this highly fluorescent amyloid dye for imaging Alzheimer's disease (AD) pathology comprising Aβ and Tau fibrils. A selection of ligands with distinct optical properties were synthesized by replacing the central benzene unit of X-34, with other heterocyclic moieties. Full photophysical characterization was performed determining absorbance and fluorescence spectra, Stokes shift, quantum yield and fluorescence lifetimes. All ligands displayed high affinity towards recombinant amyloid fibrils of Aβ1-42 (13-300 nM Kd) and Tau (16-200 nM Kd) as well as selectivity towards the corresponding disease-associated protein aggregates in AD tissue. We observed that these ligands efficiently displaced X-34, but not Pittsburgh compound B (PiB) from recombinant Aβ1-42 amyloid fibrils, arguing for retained targeting of the Congo red type binding site. We foresee that the X-34 scaffold offers the possibility to develop novel high-affinity ligands for Aβ pathology found in human AD brain in a different mode compared to PiB, potentially recognizing different polymorphs of Aβ fibrils.
      PubDate: 2018-03-15T09:58:18.242452-05:
      DOI: 10.1002/chem.201800501
  • Frontispiece: Organic-Inorganic Hybrid Materials: Multi-Functional Solids
           for Multi-Step Reaction Processes
    • Authors: Urbano Díaz; Avelino Corma
      Abstract: Nanostructured builder units are the base for the design of multifunctional hybrid catalysts, which combine catalytic efficiency with fast reactant and product diffusion. Hybrid organic-inorganic multi-site catalytic materials are important for the production of high-added-value products within the scope of chemicals and fine chemicals production. Multi-functional hybrid solids offer the possibility to combine heterogeneous (photo)catalytic reactivity together with electronic or optical properties, using only one stable and reusable material which would act as authentic catalyst-electron donor–acceptor nanoreactor capable to carry out, in one-pot, multi-step chemical reactive processes. For more information, see the Concept article by U. Díaz and A. Corma on page 3944 ff.
      PubDate: 2018-03-15T09:16:55.709178-05:
      DOI: 10.1002/chem.201881663
  • Frontispiece: The Dynamics of Chemical Reactions: Atomistic Visualizations
           of Organic Reactions, and Homage to van ’t Hoff
    • Authors: Zhongyue Yang; K. N. Houk
      Abstract: van ’t Hoff was awarded the first Nobel Prize in Chemistry in 1901 for the discovery of the laws of chemical dynamics. The study of chemical dynamics has been advanced by the development of molecular dynamics simulations and QM/MM calculations. In the first of a series entitled The Nobel Legacy, van ’t Hoff's achievements and their influence on modern chemistry are reviewed. For more details, see the Minireview by K. N. Houk and Z. Yang on page 3916 ff.
      PubDate: 2018-03-15T09:16:55.648936-05:
      DOI: 10.1002/chem.201881661
  • Frontispiece: A Novel Reconfigurable Logic Unit Based on the DNA-Templated
           Potassium-Concentration-Dependent Supramolecular Assembly
    • Authors: Chunrong Yang; Dan Zou, Jianchi Chen, Linyan Zhang, Jiarong Miao, Dan Huang, Yuanyuan Du, Shu Yang, Qianfan Yang, Yalin Tang
      Abstract: A novel reconfigurable supramolecular logic unit based on DNA-templated potassium-concentration-dependent supramolecular assembly of the triethylammonium salt of 3,3′-di(3-sulfopropyl)-4,5,4′,5′-dibenzo-9-methyl-thiacarbocyanine was designed, which could response to the input stimuli of H+ and K+ and implement a series of arithmetic and non-arithmetic functions by varying the concentrations of K+, including a half adder (HA), a half subtractor (HS) and a decoder (DC). For more information, see the Full Paper by Q. Yang on page 4019 ff.
      PubDate: 2018-03-15T09:16:54.978467-05:
      DOI: 10.1002/chem.201881665
  • Frontispiece: Enantioselective Brønsted Acid Catalysis as a Tool for the
           Synthesis of Natural Products and Pharmaceuticals
    • Authors: Jérémy Merad; Claudia Lalli, Guillaume Bernadat, Julien Maury, Géraldine Masson
      Abstract: Chiral Brønsted acids are capable of promoting plenty of enantioselective transformations. From simple substrates, chiral protons build complex enantioenriched scaffolds that are subsequently involved in the total synthesis of bioactive moieties. This review aims to describe the value of such asymmetric catalysis to the synthesis of natural products and pharmaceuticals. The target structures, and the potential disconnections are particularly emphasized. For more information see the Minireview by G. Masson and co-workers on page 3925 ff.
      PubDate: 2018-03-15T09:16:54.921068-05:
      DOI: 10.1002/chem.201881662
  • Frontispiece: Bioconjugation with Thiols by Benzylic Substitution
    • Authors: Kenji Watanabe; Takashi Ohshima
      Abstract: Conjugation between biomolecules and synthetic compounds has various applications. The picture shows that benzylic substitutions of appropriately designed reactants can be used for a selective bioconjugation with thiols in biomacromolecules. Since this reaction, involving the activation of benzylic hydroxyl group, proceeds under weakly acidic conditions, the applicable pH range differs from those of the preceding reactions. For more details, see the Communication by K. Watanabe and T. Ohshima on page 3959 ff.
      PubDate: 2018-03-15T09:16:47.780695-05:
      DOI: 10.1002/chem.201881664
  • Gold(I)-Catalysed Hydroarylation of 1,3 Disubstituted Allenes with
           Efficient Axial-to-Point Chirality Transfer
    • Authors: Daniel Sutherland; Luke Kinsman, Stuart M Angiolini, Georgina M Rosair, Ai-Lan Lee
      Abstract: Hydroarylation of enantioenriched 1,3-disubstituted allenes has the potential to proceed with axial-to-point chirality transfer to yield enantioenriched allylated (hetero)aryl compounds. However, the gold-catalysed intermolecular reaction was previously reported to occur with no chirality transfer, due to competing allene racemisation. In this full article, we describe the development of the first intermolecular hydroarylations of allenes to proceed with efficient chirality transfer, and summarise some of the key criteria for achieving high regio- and stereoselectivities.
      PubDate: 2018-03-15T06:41:22.873814-05:
      DOI: 10.1002/chem.201800209
  • Roles of Amphipathicity and Hydrophobicity in the Micelle-Driven
           Structural Switch of a 14-mer Peptide Core from a Choline-Binding Repeat
    • Authors: Héctor Zamora-Carreras; Beatriz Maestro, Erik Strandberg, Anne S. Ulrich, Jesús M. Sanz, M. Ángeles Jiménez
      Abstract: Choline-binding repeats (CBRs) are ubiquitous sequences with a β-hairpin core that are found in the surface proteins of several microorganisms such as S. pneumoniae (pneumococcus). Previous studies on a 14-mer CBR sequence derived from the pneumoccal LytA autolysin (LytA239–252 peptide) have demonstrated a switch behaviour for this peptide, so that it acquires a stable, native-like β-hairpin conformation in aqueous solution but is reversibly transformed into an amphipathic α-helix in the presence of detergent micelles. With the aim of understanding the factors responsible for this unusual β-hairpin to α-helix transition, and to specifically assess the role of peptide hydrophobicity and helical amphipathicity in the process, we designed a series of LytA239–252 variants affecting these two parameters and studied their interaction with dodecylphosphocholine (DPC) micelles by solution NMR, circular dichroism and fluorescence spectroscopies. Our results indicate that stabilising cross-strand interactions become essential for β-hairpin stability in the absence of optimal turn sequences. Moreover, both amphipathicity and hydrophobicity display comparable importance for helix stabilisation of CBR-derived peptides in micelles, indicating that these sequences represent a novel class of micelle/membrane-interacting peptides.Switch hunt: In the micelle-induced β-hairpin to α-helix switch of a 14-mer peptide derived from a choline-binding repeat, Trp sidechain interactions are essential for β-hairpin stability in aqueous solution, and both amphipathicity and hydrophobicity contribute to helix stability in the presence of detergent micelles.
      PubDate: 2018-03-15T04:42:01.919958-05:
      DOI: 10.1002/chem.201704802
  • Ti-Catalyzed Hydroamination for the Synthesis of Amine-Containing
           π-Conjugated Materials
    • Authors: Han Hao; Kyle A. Thompson, Zachary M. Hudson, Laurel L. Schafer
      Abstract: A series of conjugated enamines were prepared by Ti catalyzed anti-Markovnikov hydroamination. The synthetic route is efficient with yields of up to 94 % and the 100 % atom efficiency of the reaction means that these products are easily isolated and purified. Due to the extended conjugated system, the enamine tautomers were observed exclusively in both solid and solution phases, as determined by X-ray crystallography and NMR spectroscopy. These new conjugated molecules, with N incorporated into the backbone, show interesting photophysical properties including photo-luminescent quantum yields of up to 0.26. Notably, through the incorporation of B to give a donor–acceptor π-conjugated system, a redshift of approximately 100 nm is observed for the emission maximum along with the anticipated solvatochromic shifts.Conjugated enamines were prepared through Ti catalyzed hydroamination with high isolated yields and purity. The structure was confirmed by NMR spectroscopy and X-Ray crystallography. The photophysical properties were characterized and these molecules were found to bear high quantum yields and large solvatochromic shifts.
      PubDate: 2018-03-15T04:41:40.928054-05:
      DOI: 10.1002/chem.201704500
  • Highly Stable, New, Organic-Inorganic Perovskite (CH3NH3)2PdBr4:
           Synthesis, Structure, and Physical Properties
    • Authors: Xixia Liu; Tang Jiao Huang, Liuyang Zhang, Baoshan Tang, Nengduo Zhang, Diwen Shi, Hao Gong
      Abstract: Lead halide perovskites have attracted striking attention recently, due to their appealing properties. However, toxicity and stability are two main factors restricting their application. In this work, a less toxic and highly stable Pd-based hybrid perovskite was experimentally synthesized, after exploring different experimental conditions. This new hybrid organic-inorganic perovskite (CH3NH3)2PdBr4 was found to be an orthorhombic crystal (Cmce, Z=4) with lattice parameters a=8.00, b=7.99, c=18.89 Å. The Cmce symmetry and lattice parameters were confirmed using Pawley refinement and the atoms positions were confirmed based on DFT calculation. This perovskite compound was determined to be a p-type semiconductor, with a resistivity of 102.9 kΩ cm, a carrier concentration of 3.4 ×1012 cm−3, and a mobility of 23.4 cm2 (V s)−1. Interestingly, XRD and UV/Vis measurements indicated that the phase of this new perovskite was maintained with an optical gap of 1.91 eV after leaving in air with a high humidity of 60 % for 4 days, and unchanged for months in N2 atmosphere; much more stable than most existing organic-inorganic perovskites. The synthesis and various characterizations of this work further the understanding of this (CH3NH3)2PdBr4 organic-inorganic hybrid perovskite material.Hybrid theory: A new layered organic-inorganic hybrid perovskite (CH3NH3)2PdBr4 was obtained after trying different experimental conditions. The structure of (CH3NH3)2PdBr4 was determined and optimized. The basic physical properties are measured, showing p-type semiconductor characteristics with a 1.91 eV band gap. Impressively, (CH3NH3)2PdBr4 can stabilize its phase and properties for over four days after exposure to air with more than 60 % humidity.
      PubDate: 2018-03-15T04:31:37.297762-05:
      DOI: 10.1002/chem.201800062
  • Catalytic Enantioselective Synthesis of Highly Functionalized
           Pentafluorosulfanylated Pyrrolidines
    • Authors: Qun Zhao; Thi Minh Ha Vuong, Xing-Fen Bai, Xavier Pannecoucke, Li-Wen Xu, Jean-Philippe Bouillon, Philippe Jubault
      Abstract: The first catalytic asymmetric synthesis of highly functionalized pentafluorosulfanylated pyrrolidines is described. The method, based on a 1,3-dipolar cycloaddition reaction of aryl and heteroaryl-substituted glycine Schiff bases with pentafluorosulfanyl acrylic esters, gave access to a broad range of pyrrolidines bearing aryl, naphtyl, and heteroaryl groups. By using Xing-Phos as a catalyst, the corresponding products were obtained in good yields, good to high regioselectivity, and excellent diastereo- and enantioselectivities (up to 98 % ee). This methodology allowed the preparation of enantioenriched SF5 compounds for the first time using an enantioselective approach.Get selective! The first catalytic enantioselective synthesis of highly functionalized pentaflurorosulfanylated pyrrolidines is described. The methodology afforded access to highly functionalized pyrrolidines in good yields, with high regioselectivity and excellent diastereo- and enantioselectivities (see scheme).
      PubDate: 2018-03-15T04:30:53.875172-05:
      DOI: 10.1002/chem.201706167
  • Template-free synthesis of hierarchical SSZ-13 microspheres with high MTO
           catalytic activity
    • Authors: liancheng bing; Aixiu Tian, Fang Wang, Kaifeng Yi, Xingyuan Sun, Guangjian Wang
      Abstract: Hierarchical SSZ-13 microspheres with abundant mesoporous channels have been successfully synthesized by addition of calcined SSZ-13 crystals in the starting gel in the absence of any organic templates. This strategy not only remarkably reduces the production cost and environmental pollution but also significantly decreases the crystallization time as well as evidently reducing the zeolite crystal sizes in many cases. The synthesized sample was characterized by XRD, BET, ICP, SEM, TEM, TG, and NH3-TPD, which indicates that the organic template free synthesized SSZ-13 exhibits high crystallinity, textural properties, and acidity. Moreover, the synthesized hierarchical SSZ-13 catalyst shows outstanding performance in MTO reaction with slightly higher ethylene plus propylene selectivity and prolonged catalyst lifetime as compared to the templated SSZ-13 catalyst.
      PubDate: 2018-03-15T02:31:55.774819-05:
      DOI: 10.1002/chem.201705784
  • Cyclic Seleninate Esters, Spirodioxyselenuranes and Related Compounds -
           New Classes of Biological Antioxidants that Emulate Glutathione Peroxidase
    • Authors: Thomas George Back; Kai N. Sands, Tyler A. Tuck
      Abstract: Selenium compounds play an important role in redox homeostasis in living organisms. One of their major functions is to suppress the harmful effects of hydrogen peroxide, hydroperoxides and downstream reactive oxygen species that lead to oxidative stress, which has in turn been implicated in many diseases and degenerative conditions. The glutathione peroxidase (GPx) family of selenoenzymes plays a key protective role by catalyzing the reduction of peroxides with glutathione. Considerable effort has been expended toward the discovery of small-molecule selenium compounds that mimic GPx. To date, ebselen has been the most widely studied such compound, including in several clinical trials. However, despite its proven lack of significant toxicity, it displays only moderate catalytic activity and very poor aqueous solubility. The cyclic seleninate esters and spirodioxyselenuranes have recently been investigated as potential next generation GPx mimetics, along with structurally related selenenate esters, diazaselenuranes and pincer selenuranes. Their catalytic activities, redox mechanisms and structure-activity relationships are described in this review, along with a description and discussion of the relative merits of assays for measuring their activities.
      PubDate: 2018-03-14T22:06:15.545634-05:
      DOI: 10.1002/chem.201800182
  • Tuning optoelectronic and chiroptic properties of peptide-based materials
           by controlling the pathway complexity
    • Authors: Nazario Martin; Alicia López-Andarias, Javier López-Andarias, Carmen Atienza, Francisco J. Chichón, José L. Carrascosa
      Abstract: Supramolecular chemistry has evolved from the traditional focus on thermodynamic on-pathways to the complex study of kinetic off-pathways, which are strongly dependent of the environmental conditions. Moreover, the control over pathway complexity allows obtaining nanostructures that are inaccessible through spontaneous thermodynamic processes. Here, we present a family of peptide-based π-extended tetrathiafulvalene (exTTF) molecules which show two self-assembly pathways leading to two distinct J-aggregates, namely metastable (M) and thermodynamic (T), with different spectroscopic, chiroptical and electrochemical behavior. Moreover, cryo-transmission electron microscopy (cryo-TEM) reveals a different morphology for both aggregates and a direct observation of the morphological transformations from tapes to twisted ribbons.
      PubDate: 2018-03-14T09:08:28.253073-05:
      DOI: 10.1002/chem.201801238
  • Anion Recognition in Water, Including Sulfate, by a Bicyclam Bimetallic
           Receptor: A Process Governed by the Enthalpy/Entropy Compensatory
    • Authors: Massimo Boiocchi; Marco Bonizzoni, Carlo Ciarrocchi, Luigi Fabbrizzi, Michele Invernici, Maurizio Licchelli
      Abstract: The dimetallic system [CuII2(L)]4+ contains two facing equivalent metallocyclam subunits and incorporates ambidentate anions, mono- (halides) and poly-atomic (sulfate), which bridge the two CuII centres. Isothermal titration calorimetry (ITC) experiments in water showed that the log K values of the inclusion equilibria for halides and sulfate varied over a restricted interval (3.6±0.2), which indicated lack of selectivity and that similarity of ΔG° values resulted from the unbalanced contribution of the ΔH° and TΔS° terms: the more favourable the one, the less favourable the other. In particular, a linear dependence of ΔH° and TΔS° was observed (a typical enthalpy/entropy compensatory diagram), which assigned a major role to hydration terms: 1) a more hydrated anion resulted in a more endothermic dehydration process; and 2) a larger number of water molecules released to the solution resulted in a more positive TΔS°. Limiting cases refer to the complexation 1) of the poorly hydrated iodide (highly exothermic process, entropically disfavoured), and 2) of the highly hydrated sulfate (moderately endothermic process, entropically very favoured). Anion receptors operating in water belong to two main domains: 1) those exhibiting positive ΔH° and positive TΔS° (+/+ signature), and 2) those displaying the opposite behaviour: (−/− signature). The receptor investigated herein connects the two domains, along the ΔH°/TΔS° straight line, thanks to the hidden role of the versatile metal–anion interaction.Selectivity outside the molecule: The dicopper(II) bicyclam receptor [CuII2(L)]4+ includes ambidentate anions (halides, sulfate) in water with poor selectivity (see scheme), which is derived from conflicting enthalpy and entropy contributions: the more favourable the one contribution, the less favourable the other. This indicates the major role of solvational terms (mainly anion dehydration), which mitigate the contribution of the metal–anion interaction.
      PubDate: 2018-03-14T04:52:19.117223-05:
      DOI: 10.1002/chem.201800067
  • Azoliniums, Adducts, NHCs and Azomethine Ylides: Divergence in Wanzlick
           Equilibrium and Olefin Metathesis Catalyst Formation
    • Authors: Phillip I. Jolly; Anna Marczyk, Paweł Małecki, Osman Ablialimov, Damian Trzybiński, Krzysztof Woźniak, Silvio Osella, Bartosz Trzaskowski, Karol Grela
      Abstract: The dimerization of a saturated N-heterocyclic carbene (NHC) to tricyclic piperazine in preference to the commonly observed Wanzlick dimerization is presented. Mechanistic investigations revealed that the N-fluorene substituent of the heterocycle is implicated in both ring opening of corresponding carbene dimer and tautomerization of NHC to an azomethine ylide. This has consequences for the fate of the NHC when generated from either an azolinium salt or a pentafluorophenyl adduct. The insights gained permitted the synthesis of a new indenylidene metathesis precatalyst, which exhibits exceptional selectivity and high TONS in self-metathesis of 1-octene.NHC vs. azomethine ylide: A pentafluorophenyl NHC adduct cleanly generates corresponding N-heterocyclic carbene and a new olefin metathesis catalyst, which provides high TONS at PPM levels of loading. Both a Wanzlick and an azomethine ylide dimerization are successfully demonstrated, with the mechanism being determined by either the adduct or the azolinium NHC precursor.
      PubDate: 2018-03-14T04:51:50.848059-05:
      DOI: 10.1002/chem.201706036
  • Rhodium(I)-Catalyzed Ring-Closing Reaction of Allene-Alkene-Alkynes:
           One-Step Construction of Tricyclo[,6] and Bicyclo[6.3.0] Skeletons
           from Linear Carbon Chains
    • Authors: Yasuaki Kawaguchi; Asami Nagata, Kei Kurokawa, Haruna Yokosawa, Chisato Mukai
      Abstract: Treatment of dodecatrienyne derivatives with [RhCl(CO)2]2 in refluxing toluene effected the cycloisomerization to produce tricyclo[,6]dodecadienes. The one-carbon shortened undecatrienyne derivatives, however, afforded bicyclo[6.3.0]undecatriene derivatives instead of tricyclic compounds, the latter of which are well known as a basic skeleton of naturally occurring octanoids. On the basis of two experiments with deuterated substrates, a plausible reaction mechanism for the construction of these products was proposed.
      PubDate: 2018-03-14T03:00:42.219845-05:
      DOI: 10.1002/chem.201801239
  • A 1,5-Naphthyridine-Fused Porphyrin Dimer: Intense NIR Absorption and
           Facile Redox Interconversion with Its Reduced Congener
    • Authors: Atsuhiro Osuka; Keisuke Fujimoto
      Abstract: PtII-catalyzed cyclization of β-to-β ethynylene-bridged meso-amino NiII porphyrin dimer 4 followed by oxidation with PbO2 afforded 1,5-naphthyridine-fused porphyrin dimer 5 in good yield. This dimer possesses a redox-active 1,4-diazabutadiene linkage that is interconvertible with its reduced 1,2-diaminoethene linkage upon treatments with NaBH4 or PbO2. The dimer 5 exhibits an intense NIR absorption and a narrow HOMO-LUMO gap with a remarkably low reduction potential mainly owing to effective bonding interaction in the LUMO through the 1,4-diazabutadiene linkage. In contrast, the reduced dimer 7 is fairly electron-rich with the high HOMO energy and shows a relatively large HOMO-LUMO gap compared to that of 5.
      PubDate: 2018-03-13T22:31:47.485589-05:
      DOI: 10.1002/chem.201800854
  • Computational Screening of New Orthogonal Metal-Free Dipolar
           Cycloadditions of Mesomeric Betaines
    • Authors: Juan García de la Concepción; Martín Ávalos, Pedro Cintas, José Luis Jiménez
      Abstract: Computational strategies have gained increasing impact in the de novo design of large molecular sets targeted to a desired application. Here, we show that DFT-assisted theoretical analyses of cycloadditions involving mesoionic dipoles and strained cycloalkynes unveil a series of unexplored mesomeric betaines as vastly superior candidates for orthogonal applications. Thus, isosydnones, thiosydnones, and a six-membered homolog in particular, 6-oxo-1,3-oxazinium-4-olate, do exhibit enhanced reactivity with respect to sydnones, the archetypal mesoionic ring employed so far in orthogonal chemistry. They were spotted by assessing energy barriers and transition structures, which are largely governed by electron fluxes from dipolarophile to dipole and non-covalent interactions. The charge transfer (CT) analysis also accounts for previous experimental and theoretical results gathered in the literature, and provides a rationale for further substitution variations. The above naked dipoles release only CO2 as byproduct by retro-Diels-Alder of the resulting cycloadducts. These results should invite practitioners to have a look at such underestimated dipoles and can also help to minimize the number of experiments.
      PubDate: 2018-03-13T12:55:21.643331-05:
      DOI: 10.1002/chem.201800869
  • Template-directed synthesis of titania nanocages with four
           tetrahedrally-arranged open windows
    • Authors: Etienne Duguet; Jiaji Cheng, Nicolas Mallet, Walid Baaziz, Ovidiu Ersen, Emilie Gombart, Valérie Alard, Jérôme Majimel, Marie-Hélène Delville, Mona Tréguer-Delapierre
      Abstract: Original titania nanocages are fabricated from sacrificial silica/polystyrene tetrapod-like templates. Here are described the template synthesis, titania deposition and nanocage development through polystyrene dissolution and subsequent silica etching. Discussion about the competitive deposition of titania on the biphasic templates is particularly emphasized. The morphology of the nanocages is investigated by TEM, STEM, EDX mapping and electron tomography.
      PubDate: 2018-03-13T12:30:54.164382-05:
      DOI: 10.1002/chem.201800186
  • 9-Membered Carbocycles: Strategies and Tactics for their Synthesis
    • Authors: Tatjana Huber; Raphael E. Wildermuth, Thomas Magauer
      Abstract: Many natural products comprising a nine-membered carbocyclic core structure exhibit interesting biological effects. However, only a minority have succumbed to their synthesis in the past. The synthesis of functionalized nine-membered carbocycles still remains a challenging goal for synthetic chemists, mainly due to their high ring strain. Different strategies to overcome the unfavorable enthalpic and entropic factors associated with their formation are highlighted in this Concept article. The presented methods are classified into two different categories: (1) the ring-expansion of smaller rings or the ring-contraction of larger rings and (2) the direct cyclization of acyclic precursors.Cyclize or expand it! In this Concept article, different strategies and tactics for the challenging synthesis of functionalized nine-membered carbocycles are compared and classified into the following categories: the ring-expansion of smaller rings, the ring-contraction of larger rings, the direct cyclization of acyclic precursors and the cycloaddition/-reversion.
      PubDate: 2018-03-13T11:58:35.817631-05:
      DOI: 10.1002/chem.201705919
  • One-Pot Synthesis of Functionalized Fused Furans via a BODIPY-Catalyzed
           Domino Photooxygenation
    • Authors: Audrey Mauger; Jonathan Farjon, Pierrick Nun, Vincent Coeffard
      Abstract: Six-membered ring fused furans containing a tetrasubstituted tertiary carbon were prepared in an unprecedented one-pot BODIPY-catalyzed domino photooxygenation/reduction process. A series of functionalized furans was synthesized from readily available 2-alkenylphenols and mechanistic studies were performed to account for the domino photosensitized oxygenation.Enlightening domin1O2: In this report, a one-pot photosensitized double oxygenation/reduction process was developed. This strategy provided access to six-membered-ring fused furans containing a tetrasubstituted tertiary center.
      PubDate: 2018-03-13T11:51:11.184752-05:
      DOI: 10.1002/chem.201706087
  • Photoluminescence of Visible and NIR-Emitting Lanthanide-Doped
           Bismuth-Organic Materials
    • Authors: Rami J. Batrice; R. Lee Ayscue, Alyssa K. Adcock, Benjamin R. Sullivan, Sae Young Han, Philip M. Piccoli, Jeffery A. Bertke, Karah E. Knope
      Abstract: A bismuth-organic compound containing 2,2′:6′2“-terpyridine (terpy) and 2-thiophenecarboxylate (TC), of the general formula (terpy)Bi(κ2-TC)3⋅0.47 H2O (BiOM-1), has been synthesized under hydrothermal conditions. Addition of a lanthanide nitrate solution to the reaction mixture led to statistical replacement of the bismuth centers, and yielded isomorphous lanthanide containing compounds Bi1−xLnxOM-1 (Ln=Nd, Sm, Eu, Tb, Dy, Er, and Yb) that showed bismuth and/or ligand sensitized lanthanide-centered emission, and the first example of NIR emission from a lanthanide doped BiOM. The structure was determined by single-crystal X-ray diffraction, and the level and uniformity of lanthanide ion incorporation into the bismuth host was determined by ICP-OES and electron microprobe analysis. For the visible emitters, lifetime data and quantum yields are presented. A high efficiency of sensitization was calculated for the europium analog (50.1 %), showing significant improvement over previously reported europium thiophenecarboxylates. These novel materials may provide strategies to address concerns over the long-term sustainability of the rare earth elements, especially relating to optical devices.Host of the party: A novel bismuth- organic material has been prepared under hydrothermal reaction conditions. Doping with various lanthanide ions was achieved by introduction of aqueous lanthanide nitrate solution to the reaction mixture before heating. The crystalline products showed visible and NIR emission from the lanthanide-doped host materials, the latter of which represents the first example of lanthanide-based NIR emission from a bismuth-organic host.
      PubDate: 2018-03-13T11:51:01.427402-05:
      DOI: 10.1002/chem.201706143
  • Enhanced Li Storage Stability Induced by Locating Sn in
           Metal–Organic Frameworks
    • Authors: Na Wu; Wei Wang, Lu-Qing Kou, Xue Zhang, Ya-Ru Shi, Tao-Hai Li, Feng Li, Jing-Ming Zhou, Yu Wei
      Abstract: By locating elemental Sn in an open anionic framework, the particle cracking arising from huge volume expansion of Sn-based anode materials during lithiation/delithiation is alleviated, and the cycling stability is greatly improved. The Sn-based metal–organic framework anode material shows superior cyclic stability, with a capacity retention>92 % (after 200 cycles) and high lithium storage capacity (610 mAh g−1).Tin can: By locating elemental Sn in an open anionic framework, the particle cracking arising from huge volume expansion of Sn-based anode materials during lithiation/delithiation is alleviated, and the cycling stability is greatly improved (the capacity retention is>92 % after 200 cycles).
      PubDate: 2018-03-13T11:50:27.772858-05:
      DOI: 10.1002/chem.201800215
  • Sodium Chloride Crystal-Induced SERS Platform for Controlled Highly
           Sensitive Detection of Illicit Drugs
    • Authors: Borong Yu; Pan Li, Binbin Zhou, Xianghu Tang, Shaofei Li, Liangbao Yang
      Abstract: A sodium chloride crystal-driven spontaneous ′hot spot′ structure was demonstrated as a SERS-active platform, to get reproducible SERS signals, and eliminate the need for mapping large areas, in comparison with solution phase testing. During the process of solvent evaporation, the crystals produced induced silver aggregates to assemble around themselves. The micro-scale crystals can also act as a template to obtain an optical position, such that the assembled hot area is conveniently located during SERS measurements. More importantly, the chloride ions added in colloids can also replace the citrate and on the surface of the silver sol, and further decrease the background interference. High quality SERS spectra from heroin, methamphetamine (MAMP), and cocaine have been obtained on the crystal-driven hot spot structure with high sensitivity and credible reproducibility. This approach can not only bring the nanoparticles to form plasmonic hot spots in a controlled way, and thus provide high sensitivity, but also potentially be explored as an active substrate for label-free detection of other illicit drugs or additives.Heroin chic: A novel sodium chloride crystal-induced SERS platform is demonstrated. It possesses locations for trapping of illicit drugs with highly sensitive detection. The platform can be simply achieved by evaporation of mixture droplets including high concentration of NaCl solution, concentrated silver colloid, and illicit drug molecules on a silicon wafer.
      PubDate: 2018-03-13T11:50:22.450747-05:
      DOI: 10.1002/chem.201800487
  • Metal-Free Geminal Difunctionalization of Diazocarbonyl Compounds: A
           One-Pot Multicomponent Strategy for the Construction of α,β-Diamino
           Carbonyl Derivatives
    • Authors: Dan Zhu; Yuan Yao, Rong Zhao, Yang Liu, Lei Shi
      Abstract: An unprecedented three-component domino oxidative coupling of diazocompounds for the efficient synthesis of α-azido-β-amino esters with non-activated dimethylamino compounds and simple TMSN3 was achieved. The main features of this method include metal-free catalysis, satisfactory functional group tolerance, general applicability in complex molecule architectures, and excellent diastereoselectivity in the presence of chiral auxiliaries. In addition, several related control experiments have been conducted to investigate the reaction mechanism.A three-component domino oxidative coupling of diazocompounds for the efficient synthesis of α-azido-β-amino esters with non-activated dimethylamino compounds and simple TMSN3 is reported. Features of this method include metal-free catalysis, satisfactory functional group tolerance, general applicability in complex molecule architectures, and excellent diastereoselectivity in the presence of chiral auxiliaries.
      PubDate: 2018-03-13T11:50:16.490958-05:
      DOI: 10.1002/chem.201800555
  • Palladium-Catalyzed Asymmetric Allylic Alkylation of 4-Substituted
           Isoxazolidin-5-ones: Straightforward Access to β2,2-Amino Acids
    • Authors: Marllon Nascimento de Oliveira; Stellios Arseniyadis, Janine Cossy
      Abstract: We report here an unprecedented and highly enantioselective palladium-catalyzed allylic alkylation applied to 4-substituted isoxazolidin-5-ones. Ultimately, the process provides a straightforward access to β2,2-amino acids bearing an all-carbon quaternary stereogenic center in great yields and a high degree of enantioselectivity.Triple A approved! An unprecedented and highly enantioselective palladium-catalyzed allylic alkylation of 4-substituted isoxazolidin-5-ones is reported. The method is both high yielding and highly enantioselective, and allows a straightforward access to β2, 2-amino acids and β-lactams bearing an all-carbon α-quaternary stereogenic center.
      PubDate: 2018-03-13T11:50:05.688044-05:
      DOI: 10.1002/chem.201800641
  • RhII-Catalyzed Intermolecular C−H Arylation of Aromatics with Diazo
    • Authors: Kai Wu; Bei Cao, Cong-Ying Zhou, Chi-Ming Che
      Abstract: We developed an efficient synthesis of biaryls by a dirhodium(II)-catalyzed aromatic C−H arylation with diazo quinones. The new biaryl synthesis can be performed under mild and neutral conditions and without directing group chelation assistance. The reaction tolerates various functionalities and is applicable to a broad range of aromatics. The regioselectivity of the C−H arylation was often high and predictable. The synthetic utility of the method was demonstrated by the late-stage modifications of a series of pharmaceuticals and functional materials as well as a short synthesis of a transthyretin amyloid inhibitor.A couple of rhodium: An efficient dirhodium(II)-catalyzed aromatic C−H arylation with diazo quinones was developed. The reaction can be performed under mild and neutral conditions and without directing group chelation assistance. The C−H arylation is applicable to a broad range of aromatics with predictable regioselectivity. Late-stage modifications of a series of pharmaceuticals and functional materials as well as a short synthesis of a transthyretin amyloid inhibitor are described.
      PubDate: 2018-03-13T11:49:53.249019-05:
      DOI: 10.1002/chem.201800648
  • Direct Integration of Red-NIR Emissive Ceramic-like AnM6Xi8Xa6 Metal
           Cluster Salts in Organic Copolymers Using Supramolecular Interactions
    • Authors: Malo Robin; Noée Dumait, Maria Amela-Cortes, Claire Roiland, Maxime Harnois, Emmanuel Jacques, Hervé Folliot, Yann Molard
      Abstract: Hybrid nanomaterials made of inorganic nanocomponents dispersed in an organic host raise an increasing interest as low-cost solution-processable functional materials. However, preventing phase segregation while allowing a high inorganic doping content remains a major challenge, and usual methods require a functionalization step prior integration. Herein, we report a new approach to design such nanocomposite in which ceramic-like metallic nanocluster compounds are embedded at 10 wt % in organic copolymers, without any functionalization. Dispersion homogeneity and stability are ensured by weak interactions occurring between the copolymer lateral chains and the nanocluster compound. Hybrids could be ink-jet printed and casted on a blue LED. This proof-of-concept device emits in the red-NIR area and generates singlet oxygen, O2 (1Δg), of particular interest for lights, display, sensors or photodynamic based therapy applications.Blue Light, Red Light: High contents of phosphorescent octahedral metal clusters are homogeneously integrated within in an acrylate matrix using supramolecular interactions. The resulting hybrid materials can be processed by inkjet printing and, once deposited on a blue LED, generate bright-red-NIR light and singlet oxygen.
      PubDate: 2018-03-13T11:49:27.519038-05:
      DOI: 10.1002/chem.201800860
  • Synthesis and Identification of Aryl and Alkyl Gem-Dilithium
           Phosphido-Boranes: A Boost to the Chemistry of Phosphandiides
    • Authors: Anne Harrison-Marchand; Jie Guang, Romain Duwald, Jacques Maddaluno, Hassan Oulyadi, Sami Lakhdar, Annie-Claude Gaumont
      Abstract: The synthesis and identification of unprecedented gem-dianionic phosphorus compounds, i.e. gem-dilithium phosphido-boranes Li2[RP*BH3], with R = Ph or Cy, are reported in THF solution. Those are obtained by double deprotonation of the corresponding primary phosphine-borane precursors RPH2*BH3. Their in-depth structural study, based on multinuclear (1H, 6Li, 7Li, 11B, 13C, 31P) mono- and bi-dimensional NMR analyses, indicates a strong influence of the phosphorus substituent on the structure of the gem-dianionic phosphorus structure: while a monomeric arrangement is obtained when R = phenyl, a cyclic oligomer is observed for R = cyclohexyl. These compounds represent a new type of common handy reagents, and their access certainly insufflates the long awaited dynamic to the concept of "RP synthons" likely to be the most flexible precursors of a multitude of varied phosphorus targets.
      PubDate: 2018-03-13T09:14:21.58384-05:0
      DOI: 10.1002/chem.201800742
  • Synthesis, Structures, and Optical Properties of Azahelicene Derivatives
           and Unexpected Formation of Azahepta[8]circulenes
    • Authors: Fengkun Chen; Takayuki Tanaka, Tadashi Mori, Atsuhiro Osuka
      Abstract: Polycyclic heteroaromatic compounds including pyrrole units are promising functional scaffolds owing to their electron-rich nature, bright fluorescence, and applicability to anion recognition at the pyrrolic hydrogen. We report herein the effective synthesis of pseudo-aza[5]helicene and aza[7]helicene derivatives, and unexpected formation of azahepta[8]circulenes by oxidative fusion reactions. By choosing reaction conditions and peripheral substituents attached at the terminal indole moieties, we obtained aza[7]helicenes 10a-c and azahepta[8]circulenes 11a,c selectively in moderate to good yields. Their solid-state structures have been revealed by X-ray diffraction analysis. UV/Vis absorption, emission, and cyclic voltammetry of these compounds were studied in comparison with those of previously reported tetraaza[8]circulene (TA8C), a symmetric and planar molecule. Furthermore, the enantiomeric separation of dimethyl-substituted aza[7]helicene 10b was achieved, and the racemization kinetics have been elucidated both theoretically and experimentally. This work illustrates a wealth of advantages of pyrrole incorporation into the polycyclic aromatic scaffolds in terms of synthetic aspects, structural variation and optical tuning.
      PubDate: 2018-03-13T09:13:14.374836-05:
      DOI: 10.1002/chem.201800617
  • Access to 3-oxindoles from Allylic Alcohols and Indoles
    • Authors: Mathieu Jérôme Achard; Hortense Lauwick, Yang Sun, Huriye Akdas-Kilig, Sylvie Derien
      Abstract: The site and regioselective allylation reaction of 2-substituted indoles was carried out by using a ruthenium(IV) precatalyst containing phosphine-sulfonate chelate. Mono-, di- and tri-allylated indoles could be selectively obtained according to reaction conditions and gave only water as byproduct. The preparation of 3-oxindole derivatives was then successfully performed owing to the oxidation under air of the corresponding allylated indoles. Diallylated pseudoindoxyls were proved to be good synthons to perform cyclization through Ring Closing Metathesis affording the corresponding tricyclic adducts. Photophysical properties of 3-oxindoles have been measured, some compounds showing a strong fluorescence in water.
      PubDate: 2018-03-13T09:12:39.57851-05:0
      DOI: 10.1002/chem.201800348
  • Catalytic C-C bond-formation using a simple nickel precatalyst system:
           base- and activator-free direct C-allylation by alcohols and amines.
    • Authors: Joseph B. Sweeney; Anthony Ball, Luke Smith
      Abstract: A 'totally catalytic' nickel(0)-mediated method for base-free direct alkylation of allyl alcohols and allyl amines is reported. The reaction is selective for monoallylation, uses an inexpensive Ni(II) precatalyst system, and requires no activating reagents to be present.
      PubDate: 2018-03-13T07:55:26.405737-05:
      DOI: 10.1002/chem.201801241
  • Recent Trends in Metallopolymer Design: Redox-Controlled Surfaces, Porous
           Membranes, and Switchable Optical Materials Using Ferrocene-Containing
    • Authors: Markus Gallei; Christian Rüttiger
      Abstract: : Metallopolymers with metal functionalities are a unique class of functional materials. Their redox-mediated optoelectronic and catalytic switching capabilities, their outstanding structure formation and separation capabilities have been reported recently. Within this Minireview, scope and limitations of intriguing ferrocene-containing systems will be discussed. In the first section recent advances in metallopolymer design will be given leading to a plethora of novel metallopolymer architectures. Discussed synthetic pathways comprise controlled and living polymerization protocols as well as surface immobilization strategies. In the following sections, we focus on recent advances and new applications for side-chain and main-chain ferrocene-containing polymers as (i) remote-switchable materials, (ii) smart surfaces, (iii) redox-responsive membranes, and some recent trends in (iv) photonic structures and (v) other optical applications.
      PubDate: 2018-03-13T07:25:29.797288-05:
      DOI: 10.1002/chem.201800412
  • PSYCHE Pure Shift NMR Spectroscopy
    • Authors: Mohammadali Foroozandeh; Gareth Morris, Mathias Nilsson
      Abstract: Broadband homodecoupling techniques in NMR, also known as "pure shift" methods, aim to enhance spectral resolution by suppressing the effects of homonuclear coupling interactions to turn multiplet signals into singlets. Such techniques typically work by selecting a subset of "active" nuclear spins to observe, and selectively inverting the remaining, "passive", spins to reverse the effects of coupling. Pure Shift Yielded by Chirp Excitation (PSYCHE) is one such method; it is relatively recent, but has already been successfully implemented in a range of different NMR experiments. Paradoxically, PSYCHE is one of the trickiest of pure shift NMR techniques to understand but one of the easiest to use. Here we offer some insights into theoretical and practical aspects of the method, and into the effects and importance of the experimental parameters. Some recent improvements that enhance the spectral purity of PSYCHE spectra will be presented, and some experimental frameworks including examples in 1D and 2D NMR spectroscopy, for the implementation of PSYCHE will be introduced.
      PubDate: 2018-03-13T06:30:56.022338-05:
      DOI: 10.1002/chem.201800524
  • APTRA-based luminescent lanthanide complexes displaying enhanced
           selectivity for Mg2+
    • Authors: David Parker; Edward Walter, Gareth Williams
      Abstract: A series of three europium(III) complexes has been created in which an APTRA moiety has been integrated into the sensitising chromophore (APTRA = o-aminophenol-N,N,N-triacetate). The constitutionally isomeric complexes EuL1 and EuL2 feature the APTRA unit linked to a metal-bound pyridine ring through an alkynyl unit, differing according to the disposition of the APTRA substituents relative to the C≡C unit (para-N and para-O respectively). In EuL3, the APTRA ring is directly bonded to the Eu-coordinated pyridine (para-O). The metal binding affinities for magnesium, calcium and zinc ions have been measured using emission and excitation spectroscopy. The pyridylalkynylaryl systems, EuL1 and EuL2, offer superior affinity and selectivity for Mg2+. The Mg2+ affinities are surprisingly very different from prior studies on structurally related systems that incorporate organic fluorophores as reporters, as opposed to the macrocyclic Eu complex moiety. A much reduced affinity for calcium and zinc - possibly arising from the lower donor ability of the aryl N or O atoms arising from extended conjugation - means that magnesium ion concentrations can be measured directly in serum for the first time, using such an approach. An apparent dissociation constant for magnesium binding of Kd = 2.4 mM was calculated in the serum background.
      PubDate: 2018-03-13T05:56:42.449313-05:
      DOI: 10.1002/chem.201800745
  • Two Discrete RuCp*-Binding Modes of N-Confused Porphyrins: Peripheral
           π-Complex and Sitting Atop Ruthenocenophane Complex via Skeletal
    • Authors: Takaaki Yamamoto; Koki Mitsuno, Shigeki Mori, Shuhei Itoyama, Yoshihito Shiota, Kazunari Yoshizawa, Masatoshi Ishida, Hiroyuki Furuta
      Abstract: Complexation of a RuCp* cation with N-confused tetraarylporphyrins (NCPs) forms directly bound ruthenium(II) pentamethylcyclopentadienyl (Cp*) π-complex on a specific meso-aryl group (e.g., phenyl) neighbouring peripheral imino nitrogen of NCPs in high yields. In contrast, in the case of NCPs bearing bulky meso-substituents (e.g., 3,5-di-tert-butylphenyl), novel ruthenocenophane-like complex embedded on an N-confused calix[4]phyrin was formed through multiple C-H bond activation of methyl groups of Cp* ligand. The mechanistic insight into the formation of the ruthenocenophane was derived from DFT calculations.
      PubDate: 2018-03-13T05:25:34.497449-05:
      DOI: 10.1002/chem.201801237
  • Radicals and Sulfur Dioxide: A Versatile Combination for the Construction
           of Sulfonyl-Containing Molecules
    • Authors: Kamil Hofman; Nai-Wei Liu, Georg Manolikakes
      Abstract: Molecules containing a sulfonyl functionality, such as sulfones, sulfonyl chlorides or sulfonamides play an important role in organic chemistry and have found widespread application, especially in the construction of biologically active compounds. Recently, methods for the synthesis of the sulfonyl moiety utilizing sulfur dioxide as a key building block have received considerable attention. In this context, radical-based transformations with sulfur dioxide have emerged as a new and attractive approach for the construction of the sulfonyl functional group. This short review highlights recent advances in the use of sulfur dioxide in radical reactions and covers the historical background, which forms the basis for these current progresses. Limitations of the existing methods and potential further developments will be discussed.Radical-based transformations with sulfur dioxide have emerged as attractive new tool for the synthesis of sulfones, sulfonamides or sulfonyl chlroides. This minireview covers the historical background and recent progress in this area.
      PubDate: 2018-03-13T03:51:44.872958-05:
      DOI: 10.1002/chem.201705470
  • A Neutral RuII Hydride Complex for the Regio- and Chemoselective Reduction
           of N-Silylpyridinium Ions
    • Authors: Susanne Bähr; Martin Oestreich
      Abstract: A detailed experimental analysis of the 1,4-selective reduction of pyridine with hydrosilanes catalyzed by a coordinatively unsaturated RuII thiolate complex is reported. The previously suggested intermediates, N-silylpyridinium ions and a neutral RuII hydride, have been independently synthesized and do indeed participate in the catalytic cycle. The resting state is not the cationic RuII complex initially used as the catalyst but its pyridine-coordinated congener. All RuII complexes, including the one resulting from hydrosilane activation, are in equilibrium with each other. The N-silylated 1,4-dihydropyridine together with the cationic RuII complex convert back into the corresponding N-silylpyridinium ion and the neutral RuII hydride (retro-hydrosilylation), followed by further backward reaction into the hydrosilane and the pyridine adduct of the cationic complex. These steps prove the overall reversibility of the transformation.There and back again: The 1,4-hydrosilylation of pyridines catalyzed by a RuII thiolate complex is mechanistically investigated. Stoichiometric experiments with independently synthesized intermediates made it possible to refine the initial proposal; equilibria between three different RuII complexes are part of this reversible (retro-)hydrosilylation.
      PubDate: 2018-03-13T03:51:31.098835-05:
      DOI: 10.1002/chem.201705899
  • A Conductive Self-healing Double Network Hydrogel with Toughness and Force
    • Authors: Shunli Liu; Kewen Li, Imtiaz Hussain, Olayinka Oderinde, Fang Yao, Jiuyang Zhang, Guo Dong Fu
      Abstract: Mechanically-tough and electrical conductive self-healing hydrogels may have broad applications in wearable electronics, health-monitoring systems, and smart robotics in the following years. Here, we proposed a new design strategy to synthesize a dual physical cross-linked polyethylene glycol/poly(acrylic acid) (PEG/PAA) double network hydrogel, consisting of an ferric ions cross-linked linear chain extension of PEG (2, 6-pyridinedicarbonyl moieties incorporated in the PEG backbone, PEG-H2pdca) as the first physical network and a PAA-Fe3+ gel as the second physical network. Metal ions coordination and double network structure enable the DN hydrogel to withstand up to 0.4 MPa tensile stress and 1560 % elongation at break, and the healing efficiency reaches 96.8 % in 12 h. In addition, due to the dynamic ions transfer in the network, the resulting hydrogels exhibit controllable conductivity (0.0026 - 0.0061 S/cm) and stretch sensitivity. These functional self-healing hydrogels have potential applications in electronic skin. We envision that this strategy also can be employed to prepare other high-performance and multi-functional polymers.
      PubDate: 2018-03-13T00:01:28.133973-05:
      DOI: 10.1002/chem.201800259
  • Assembly of Tetrahydropyran Derivatives from Aldehydes, Allylboronates and
           Syngas by Asymmetric Relay Catalytic Cascade Reaction
    • Authors: Liuzhu Gong; Lu-Lu Li, Yong-Liang Su, Zhi-Yong Han
      Abstract: An efficient synthesis of highly enantioenriched tetrahydropyrans from readily available aldehydes, allylboronates and syngas has been established by multiply relay catalysis of rhodium and chiral phosphoric acid. The cascade reaction integrates the asymmetric allylboration of aldehydes and alkene hydroformylation, providing structurally diverse range of products with different workup procedures. The concise synthesis of key chiral building blocks to access herboxidiene and leucascandrolide A demonstrates the high synthetic utility of this method. The cascade reactions employing alkenes to replace aldehydes was also successful.
      PubDate: 2018-03-12T22:02:42.028582-05:
      DOI: 10.1002/chem.201801197
  • Heterogeneous Pyrophosphate Linked DNA-Oligonucleotides: Aversion for DNA
           but Affinity for RNA
    • Authors: Brooke Anderson; Ramanarayanan Krishnamurthy
      Abstract: Pyrophosphate linkages are important in extant biology and are hypothesized to have played a role in prebiotic chemistry and in the origination of oligonucleotides. Inspired by the possible role of pyrophosphate as backbones of primordial oligomers, we synthesized DNA oligomers with varying amounts of pyrophosphate inserts (ppDNA) and investigated their base-pairing properties. As expected, with increasing amounts of pyrophosphate inserts in the backbone the thermal stability of ppDNA-DNA duplexes was compromised. In contrast, the ppDNA-RNA duplex exhibited, remarkably, duplex stability even with accumulation of pyrophosphate linkages. The favorable accommodation of pyrophosphate linkages within a ppDNA-RNA (vis-à-vis a ppDNA-DNA) duplex structure seems to be a consequence of the increase in diameter of the double-helix with eight-bond repeat units, and higher inclination of the base-pair-axis with respect to the backbone in RNA (A-form), as compared to DNA (B-form). These results suggest that pyrophosphate linked oligonucleotides could harbor functional capabilities with implications for their roles in origins of life and backbone designs in chemical biology.
      PubDate: 2018-03-12T22:02:22.261552-05:
      DOI: 10.1002/chem.201800538
  • 2D and 3D Coordination Networks of Polynuclear Bismuth Oxido/Hydroxido
           Sulfonato Clusters from Low Temperature Solid-State Metathesis Reactions
    • Authors: Philip C. Andrews; Dimuthu Senevirathna, Melissa Werrett, Victoria Blair, Michael Mehring
      Abstract: Solid-state metathesis (SSM) reactions between Bi(NO3)3*5H2O and potassium benzene-1,2-disulfonate (= 1,2-BDSK2), sodium benzene-1,3-disulfonate (= 1,3-BDSNa2) allows access to the first 2D; {[Bi6O4(OH)4(1-2BDS)2(NO3)2*4H2O]*11H2O}∞ and {[Bi22O24(OH)6(1,3-BDS)6*12DMSO]*3DMSO*4H2O}∞, and 3D, {[Bi6O4(OH)4(1,3-BDS)3*4H2O]*6H2O}∞, polymeric networks of sulfonato encapsulated polynuclear bismuth oxido/hydroxido clusters
      PubDate: 2018-03-12T22:02:02.863885-05:
      DOI: 10.1002/chem.201705981
  • Towards the Next Generation of Lochmann-Schlosser Superbases: a Potassium
           Neopentyl/Alkoxy Aggregate used in the Tetra-Functionalisation of
    • Authors: Jan Klett
      Abstract: Lochmann‒Schlosser superbases are formed by mixing alkyllithium with potassium alkoxides. These reagents could prove their synthetic usefulness and reliability in many reactions over five decades. However, despite many efforts the real source of the exceptional reactivity remained a secret. The seemingly manageable system of four components (lithium, potassium atoms, alkyl groups, and alkoxy groups) and their interaction is obscured by poor solubility and fierce reactivity. Recent progress was achieved by using neopentyllithium, leading to alkane soluble-aggregates with varying lithium/potassium content and a flexible alkyl/alkoxy ratio. In this work we isolated two new alkane-soluble alkyl/alkoxy mixed aggregates, [Li4KNp2(OtBu)3] and [K4Np(OtAm)3]. The latter compound is a thermally-stable three-component potassium alkyl/alkoxy base with well-defined stoichiometry in contrast to lithium-containing Lochmann-Schlosser bases with variable metal and alkyl/alkoxy content. In a simple protocol this potassium base produced tetrametalated ferrocene which was converted into 1,1',3,3'-ferrocenetetracarboxylic acid by reaction with CO2. A subsequent conversion into the methyl ester allowed its separation from accompanying di- and tri-substituted ferrocenes.
      PubDate: 2018-03-12T13:05:32.562491-05:
      DOI: 10.1002/chem.201800608
  • 2-(Hydroxyimino)aldehydes: Photochemical and Physico-Chemical Properties
           of a versatile functional group for monomer design
    • Authors: Patrizia Gentili; Martina Nardi, Irene Antignano, Paolo Cambise, Marco D'Abramo, Francesca D'Acunzo, Alessandro Pinna, Emanuele Ussia
      Abstract: In the context of our research on stimuli-responsive polymers bearing the 2-(hydroxyimino)aldehyde (HIA) group, we explore the photochemical behavior and physico-chemical properties of a number of HIAs. Interpretation of experimental data is supported by quantum mechanical calculations. HIAs are expected to undergo photoisomerization, chelate metal ions, yield hydrogen-bonded dimers or oligomers, exhibit relatively low pKas, and form>C=NO* radicals through OH hydrogen abstraction or oxidation of the oximate ion. Besides the well-established E/Z oxime photoisomerism, we observe a Norrish-Yang cyclization resulting in cyclobutanol oximes, to our knowledge not described in previous literature. Acidity, Bond Dissociation Enthalpies and electrochemical properties of HIAs are compared to literature data on simple oximes. Results are discussed in relation to the many potential applications for HIAs, with emphasis on the synthesis of novel HIA-containing responsive polymers.
      PubDate: 2018-03-12T09:55:43.278757-05:
      DOI: 10.1002/chem.201800059
  • Synthesis and Immunological Studies of Oligosaccharides Consisting of the
           Repeating Unit of Streptococcus pneumoniae Serotype 3 Capsular
    • Authors: Chenghe Xiong; Shaojie Feng, Yin Qiao, Zhongwu Guo, Guofeng Gu
      Abstract: A highly convergent and efficient strategy was developed for the synthesis of complex oligosaccharides of Streptococcus pneumoniae type 3 capsular polysaccharide containing multiple glucuronic acid units. After oligoglucosides were effectively and stereoselectively assembled, the designated glucose units were regioselectively oxidized to glucuronic acid in one step at the final synthetic stage, which helped avoid difficult glycosylations involving glucuronic acid. The target oligosaccharides had a free amino group at the reducing end and varied caps at the non-reducing end to enable further modification and structure-activity relationship study. Immunological evaluation of the oligosaccharide-tetanus toxoid conjugates showed that they elicited robust T cell-dependent IgG antibody responses and that the sugar chain length had a major impact on their immunological properties. In particular, the penta- and hexasaccharides were identified as promising antigens for vaccine development.
      PubDate: 2018-03-12T07:55:30.897485-05:
      DOI: 10.1002/chem.201800754
  • Computational Characterization of the Mechanism for the Oxidative Coupling
           of Benzoic Acid and Alkynes by Rh/Cu and Rh/Ag Systems
    • Authors: Ignacio Funes-Ardoiz; Feliu Maseras
      Abstract: DFT calculations are applied to the study of the oxidative coupling between benzoic acid and 1-phenyl-1-propyne catalyzed by [CpRhCl2]2 using either Cu(OAc)2(H2O) or Ag(OAc) as terminal oxidants, a process that has been experimentally shown to have subtleties related to regioselectivity (placement of the phenyl substituent of the alkyne in the isocoumarin product) and chemoselectivity (isocoumarin or naphthalene derivatives). Calculations reproduce the experimental results, and show the involvement of the oxidant throughout the catalytic cycle. The regioselectivity is decided in the alkyne insertion step, in particular by the relative arrangement between two phenyl groups. The high chemoselectivity towards isocoumarin associated to Cu(OAc)2(H2O) is explained because the copper moiety blocks the CO2 extrusion pathway that would lead to naphthalene derivatives, something that does not happen when Ag(OAc) is used.
      PubDate: 2018-03-12T06:55:59.784311-05:
      DOI: 10.1002/chem.201800627
  • A green-LED driven source of hydrated electrons characterized from
           microseconds to hours and applied to cross couplings
    • Authors: Robert Naumann; Martin Goez
      Abstract: We present a novel photoredox catalytic system that delivers synthetically useable concentrations of hydrated electrons when illuminated with a green light-emitting diode (LED). The catalyst is a ruthenium complex protected by an anionic micelle, and the urate dianion serves as sacrificial donor confined to the aqueous bulk. Through its chemical properties, that donor not only suppresses charge recombination that would limit the electron yield but also enables this system to perform cross couplings via hydrated electrons, for which we report the first examples. We have investigated the kinetics of all the steps involving the electron and its direct precursor in a comparative study by using laser flash photolysis and by monitoring product formation during LED photolysis. Despite the differences in timescales, each approach on its own already gives a complete picture of the reaction over a temporal range ten orders of magnitude wide. Noticeable discrepancies between the kinetic parameters obtained with the two complementary techniques can be rationalized with the slow secondary chemistry of the system; they reveal that the product-based method provides a more accurate description because it responds also to the changes of the system composition during a synthesis; hence, they demonstrate that in complex systems the timescale of the experimental observation should be matched to that of the actual application.
      PubDate: 2018-03-12T06:25:29.485902-05:
      DOI: 10.1002/chem.201800626
  • Dimerization of the Benzyl Radical in a High-Temperature Pyrolysis
           Reactor, investigated by IR/UV ion dip spectroscopy
    • Authors: Florian Hirsch; Philipp Constantinidis, Ingo Fischer, Sjors Bakels, Anouk Rijs
      Abstract: We investigate the self-reaction of benzyl, C7H7 in a high tempera-ture pyrolysis reactor. The work is motivated by the observation that resonance-stabilized benzyl radicals can accumulate in reactive environments and contribute to the formation of polycyclic aromatic hydrocarbons (PAH) and soot. Reaction products are detected by IR/UV ion dip spectroscopy, using infrared radiation from the free electron laser FELIX, and are identified by comparison with com-puted spectra. Among the reaction products identified by their IR absorption are several PAH linked to toluene combustion such as bibenzyl, phenanthrene, diphenylmethane and fluorene. The identi-fication of 9,10-dihydrophenanthrene provides evidence for a mechanism of phenanthrene formation from bibenzyl that proceeds via initial cyclization rather than an initial hydrogen loss to stilbene.
      PubDate: 2018-03-12T05:56:53.814648-05:
      DOI: 10.1002/chem.201800852
  • Dibenzo[a,e]pentalenophanes - Bending a Non-Alternant Hydrocarbon
    • Authors: Mathias Hermann; Daniel Wassy, Daniel Kratzert, Birgit Esser
      Abstract: In cyclophanes an aromatic moiety is incorporated into a (strained) cyclic structure. Of particular interest as model systems for bent carbon nanostructures are those containing polycyclic aromatic hydrocarbons. Dibenzo[a,e]pentalene (DBP) is a non-alternant polycyclic hydrocarbon with small bandgap and tunable optoelectronic properties. However, changing these properties by bending of the DBP structure have yet to be investigated. Herein, we report the synthesis, optoelectronic and structural properties of (2,7)dibenzo[a,e]pentalenophanes with four different bridge sizes and bending angles of the DBP unit, accompanied by (TD)DFT calculations. The last, strain-inducing dehydration reaction was accomplished using the Burgess reagent. The HOMO and LUMO levels and the magnetic shielding of protons pointing inside the cyclophane cavity grew stepwise with increasing ring strain. Single crystal X-ray structures of the smallest three derivatives revealed a near semi-circle and a bend angle of the DBP unit of almost 88° for the smallest derivative. We demonstrated the synthetic versatility of our approach by varying the substituents at the DBP unit, allowing for a further tuning of optoelectronic properties. The synthetic strategy presented herein may pave the way for the synthesis of conjugated DBP nanorings.
      PubDate: 2018-03-12T05:25:57.171357-05:
      DOI: 10.1002/chem.201800322
  • Superconductivity in the 2-Dimensional Homologous Series AMmBi3Q5+m (m =
           1, 2) (A = Rb, Cs; M = Pb, Sn; Q = Se, Te)
    • Authors: Christos Malliakas; Duck Young Chung, Helmut Claus, Mercouri G Kanatzidis
      Abstract: Superconductivity in the two-dimensional AMmBi3Q5+m family of semimetals is reported. The AMBi3Te6 (m = 1) and AM2Bi3Te7 (m = 2) members of the homologous series with A = Rb, Cs and M = Pb, Sn undergo a bulk superconducting transition ranging from 2.7 to 1.4 K depending on the composition. The estimated superconducting volume fraction is about 90%. Superconducting phase diagrams as a function of chemical pressure are constructed for the solid solution products of each member of the homologous series, AMBi3-xSbxTe6-ySey and AM2Bi3-xSbxTe7-ySey (0 ≤ x ≤ 3 or 0 ≤ y ≤ 2). The structural flexibility of the ternary AMmM'3Te5+m semiconducting homology to form isostructural analogues with a variety of metals M = Pb, Sn; M' = Bi, Sb gives access to a large number of electronic configuration and superconductivity due to chemical pressure effects.
      PubDate: 2018-03-12T03:26:06.150085-05:
      DOI: 10.1002/chem.201800883
  • A Synthetic Approach for the Rapid Preparation of BODIPY Conjugates and
           their use in Imaging of Cellular Drug Uptake and Distribution
    • Authors: Sona Krajcovicova; Jarmila Stankova, Petr Dzubak, Marian Hajduch, Miroslav Soural, Milan Urban
      Abstract: A solid-phase synthetic (SPS) method was developed for the preparation of BODIPY-labeled bioactive compounds that allows for fast and simple synthesis of conjugates for use in fluorescent microscopy. The approach was used to visualize cellular uptake and distribution of cytotoxic triterpenes in cancer cells.Solid-phase labeling: Solid-phase synthesis was used to prepare BODIPY-labeled bioactive compounds for the rapid synthesis of conjugates for use in fluorescent microscopy. The approach was used to visualize cellular uptake and distribution of cytotoxic triterpenes in cancer cells.
      PubDate: 2018-03-12T03:15:01.807775-05:
      DOI: 10.1002/chem.201706093
  • Iron Carbides and Nitrides: Ancient Materials with Novel Prospects
    • Authors: Zhantong Ye; Peng Zhang, Xiang Lei, Xiaobai Wang, Nan Zhao, Hua Yang
      Abstract: Iron carbides and nitrides have aroused great interest in researchers, due to their excellent magnetic properties, good machinability and the particular catalytic activity. Based on these advantages, iron carbides and nitrides can be applied in various areas such as magnetic materials, biomedical, photo- and electrocatalysis. In contrast to their simple elemental composition, the synthesis of iron carbides and nitrides still has great challenges, particularly at the nanoscale, but it is usually beneficial to improve performance in corresponding applications. In this review, we introduce the investigations about iron carbides and nitrides, concerning their structure, synthesis strategy and various applications from magnetism to the catalysis. Furthermore, the future prospects are also discussed briefly.Hard as iron: Known to all, iron carbides and nitrides, a series of particular structures with complex bond interactions, have attracted much attention due to excellent mechanical, magnetic and catalytic properties. Furthermore, nanocomposite materials associated with iron carbide and nitride have been used in biomedical, electrochemical catalysis, energy storage, and other fields and have shown extraordinary performance. This article summarizes the structure, synthesis, and application of iron carbides and nitrides.
      PubDate: 2018-03-12T01:51:04.822273-05:
      DOI: 10.1002/chem.201706028
  • Cyclolinear Oligo- and Poly(iminoborane)s: The Missing Link in Inorganic
           Main-Group Macromolecular Chemistry
    • Authors: Ozan Ayhan; Nicolas A. Riensch, Clemens Glasmacher, Holger Helten
      Abstract: The reaction of n-C8H17B[N(Me)SiMe3]2 (1) with n-C8H17BCl2 (2 a) yielded, instead of a linear poly(iminoborane), the aminoborane n-C8H17B(Cl)N(Me)SiMe3 (4) and after cyclotrimerization the borazine cyclo-(n-C8H17BNMe)3 (6). Side reactions that result in borazine formation were effectively suppressed if 1,3-bis(trimethylsilyl)-1,3,2-diazaborolidines 7 were employed as co-monomers in combination with dichloro- or dibromoboranes 2 or 8, respectively. Silicon/boron exchange polycondensation led to oligo(iminoborane)s 11 a,b,ac,d. Alternative synthetic routes to such species involve Sn/B exchange of 1,3-bis(trimethylstannyl)-2-n-octyl-1,3,2-diazaborolidine (16) and n-C8H17BBr2 (8 a), and the initiated polycondensation of the dormant monomer 14 in the presence of a Brønsted acid (HCl, HOTf, or HNTf2; Tf=trifluoromethylsulfonyl). Although an attempt to obtain an oligo-/poly(iminoborane) with phenyl side groups yielded only insoluble material, the incorporation of aryl groups was proven for a derivative with both phenyl and n-octyl boron substituents (11 ac), as well as for a derivative with 4-n-butylphenyl side groups (11 d). The highest-molecular-weight sample obtained was 11 ac. Featuring about 18 catenated BN units, on average, this is the closest approach to a poly(iminoborane) known.Drawing a line under polymerization: Well-defined oligo(iminoborane)s with up to 18 catenated BN units, on average, were prepared by Si/B or Sn/B exchange polycondensation and initiated polymerization of a dormant monomer (see scheme). The cyclolinear backbone imparts high stability and precludes the unwanted formation of borazine byproducts. The properties of the new materials are effectively tuned by variation of their side groups.
      PubDate: 2018-03-12T01:47:47.791913-05:
      DOI: 10.1002/chem.201705913
  • Phenylene Bridged Cyclic Azaacenes: Dimers and Trimers
    • Authors: Sebastian Hahn; Silke Koser, Manuel Hodecker, Pascal Seete, Frank Rominger, Ognjen Š. Miljanić, Andreas Dreuw, Uwe H. F. Bunz
      Abstract: The synthesis and characterization of novel macrocyclic, phenylene-bridged azaacenes is reported. These species were obtained either by a conventional benzoin– diamine condensation, as shown for the case of the cyclotrimers, in which the azaacene units are separated by meta-connected phenylene bridges, or by a Buchwald–Hartwig-type Pd-catalyzed coupling, which employs 1,2,5,6-tetrabromodibenzocyclooctatetraene as the substrate and bis-TIPS-ethynylated diaminobenzene, -naphthalene or -anthracene as the coupling partner to give the double coupling products azaacene-annulated dibenzocyclooctatetraenes in moderate yields. The macrocycles show strong emission and light emitting diodes have been built with brightnesses exceeding 1600 cd m−2. We evaluated the optical and electronic properties and the solid-state structures of the molecules and discuss their properties through comparison with their linear and tetrameric N-heteroacene counterparts.Bright and colourful: Different macrocyclic, phenylene-bridged azaacenes were obtained by condensation reations and Buchwald–Hartwig-type couplings in a two step synthesis. We evaluated the optical and electronic properties, use the targets as emitting materials in OLEDs and discuss their properties through comparison with their linear and tetramer N-heteroacene counterparts.
      PubDate: 2018-03-12T01:47:31.661219-05:
      DOI: 10.1002/chem.201705704
  • Synthesis and HNO Donating Properties of the Piloty's Acid Analogue
           Trifluoromethanesulphonylhydroxamic acid: Evidence for Quantitative
           Release of HNO at Neutral pH Conditions
    • Authors: Sonya K Adas; Vinay Bharadwaj, Yang Zhou, Jiuhong Zhang, Alexander J. Seed, Nicola Elizabeth Brasch, Paul Sampson
      Abstract: Trifluoromethanesulphonylhydroxamic acid, CF3SO2NHOH, is shown to release HNO under physiological pH conditions. A two-step synthesis is presented with the first complete characterization of CF3SO2NHOH. This molecule rapidly decomposes in neutral aqueous solution to cleanly release HNO and CF3SO2-, demonstrated using the HNO traps TXPTS and HOCbl, and by 19F NMR spectroscopy.
      PubDate: 2018-03-11T21:56:14.318236-05:
      DOI: 10.1002/chem.201800662
  • Deciphering the Surface Composition and the Internal Structure of Alloyed
           Silver-Gold Nanoparticles
    • Authors: Viktoria Grasmik; Christian Rurainsky, Kateryna Loza, Mathies V Evers, Oleg Prymak, Marc Heggen, Kristina Tschulik, Matthias Epple
      Abstract: Spherical bimetallic AgAu nanoparticles in the molar ratios 30:70, 50:50, and 70:30 with a diameter of 30 to 40 nm were analyzed together with pure silver and gold nanoparticles of the same size. Dynamic light scattering (DLS) and differential centrifugal sedimentation (DCS) were used for size determination. Cyclic voltammetry (CV) was used to determine the nanoalloy composition, together with atomic absorption spectroscopy (AAS), energy-dispersive X-ray spectroscopy (EDX) and Ultraviolet-visible (UV/vis) spectroscopy. Underpotential deposition (UPD) of lead (Pb) on the particle surface gave information about its spatial elemental distribution and surface area. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) were applied to study the shape and the size of the nanoparticles. X-ray powder diffraction gave the crystallite size and the microstrain. The particles form a solid solution (alloy) with an enrichment of silver on the nanoparticle surface, including some silver-rich patches. UPD indicated that the surface only consists of silver atoms.
      PubDate: 2018-03-09T12:50:21.739445-05:
      DOI: 10.1002/chem.201800579
  • The physico-chemical basis of DNA radiosensitization - Implications for
           cancer radiation therapy
    • Authors: Robin Schürmann; Stefanie Vogel, Kenny Ebel, Ilko Bald
      Abstract: High-energy radiation is used in combination with radiosensitizing therapeutics to treat cancer. The most common radiosensitizers are halogenated nucleosides and cisplatin derivatives, and recently also metal nanoparticles have been suggested as potential radiosensitizing agents. The radiosensitizing action of these compounds can at least partly be ascribed to an enhanced reactivity towards secondary low-energy electrons generated along the radiation track of the high-energy primary radiation, or to an additional emission of secondary reactive electrons close to the tumour tissue. This is referred to as physico-chemical radiosensitization. In this Concept Article we present current experimental methods used to study fundamental processes of physico-chemical radiosensitization and discuss the most relevant classes of radiosensitizers. Open questions in the current discussions are identified and future directions outlined, which can lead to optimized treatment protocols or even novel therapeutic concepts.
      PubDate: 2018-03-09T09:56:48.68864-05:0
      DOI: 10.1002/chem.201800804
  • Heterolytic Si‒H bond cleavage at a molybdenum oxido based Lewis
    • Authors: Niklas Zwettler; Simon Walg, Ferdinand Belaj, Nadia C. Mösch-Zanetti
      Abstract: Reaction of a molybdenum(VI) oxido imido complex with the strong Lewis acid B(C6F5)3 gave access to the Lewis adduct [Mo{OB(C6F5)3}(NtBu)L2] featuring reversible B‒O bonding in solution. The resulting FLP-like reactivity is reflected by the compound's ability to heterolytically cleave Si‒H bonds, leading to a clean formation of the novel cationic Mo(VI) species 3a (R=Et) and 3b (R=Ph) of the general formula [Mo(OSiR3)(NtBu)L2][HB(C6F5)3]. These compounds possess properties highly unusual for molybdenum d0 species such as an intensive, charge‒transfer based color as well as a reversible redox couple at very low potentials, both dependent on the employed silane. Single-crystal X-ray diffraction analyses of 2 and 4b, a derivative of 3b featuring the [FB(C6F5)3]‒ anion, picture the stepwise elongation of the Mo=O bond, leading to a large increase in the electrophilicity of the metal center. The reaction of 3a and 3b with benzaldehyde allowed for the regeneration of compound 2 by hydrosilylation of the benzaldehyde. NMR spectroscopy suggested an unusual mechanism for the transformation, involving a substrate insertion in the B‒H bond of the borohydride anion.
      PubDate: 2018-03-09T07:22:31.703748-05:
      DOI: 10.1002/chem.201800226
  • Regium-π bonds: An unexplored link between noble metal nanoparticles
           and aromatic surfaces.
    • Authors: Antonio Bauzá; Antonio Frontera
      Abstract: In this study the ability of metal clusters involving elements from group IB (Ag, Cu and Au) to favourably interact with π-systems of different size and electronic nature has been evaluated at the PBE0-D3/def2-TZVPP//PBE0-D3/def2-TZVP level of theory. We have used M9 clusters (M = Cu, Ag and Au) as σ-hole and σ-lump donors and benzene, trifluorobenzene and hexafluorobenzene as aromatic rings. In addition, we have expanded our study to the analysis of extended π-systems by using naphthalene and anthracene moieties as well as their corresponding perfluorinated derivatives. Furthermore, we have used Bader's theory of "Atoms in Molecules" as well as NBO (Natural Bonding Orbital) and Spin Density calculations to further investigate and characterize the regium-π and σ-lump complexes described herein. As far as our knowledge extends, regium-π bonds have not been previously described in the literature and may be of great importance in the understanding of organocatalytic processes involving aromatic substrates as well as in the design of new materials based on this novel subclass of σ-hole bonding.
      PubDate: 2018-03-09T06:21:47.748705-05:
      DOI: 10.1002/chem.201800820
  • Subnaphthalocyanines as electron acceptors in polymer solar cells:
           improving device performance via modifying peripheral and axial
    • Authors: Rene Janssen; Chunhui Duan, Fallon Colberts, David Guzmán, Tomas Torres
      Abstract: A new class of subnaphthalocyanines bearing various peripheral and axial substituents have been synthesized for use as electron acceptors in solution-processed bulk-heterojunction polymer solar cells. The resulting solar cells exhibit modest photovoltaic performance with contributions from both the polymer donor and subnaphthalocyanine acceptor to the photocurrent.
      PubDate: 2018-03-09T06:21:14.142918-05:
      DOI: 10.1002/chem.201800596
  • Dual-selective and dual-enhanced SERS nanoprobes strategy for circulating
           hepatocellular carcinoma cells detection
    • Authors: Xiao Rui
      Abstract: The detection of hepatocellular carcinoma (HCC) circulating tumor cells (CTCs) from a blood sample can be a very powerful noninvasive approach for the early detection and therapy of liver cancer. However, the extremely rare cells in blood containing billions of other cells make the capture and identification of CTCs with sufficient sensitivity and specificity a real challenge. Here, a magnetically assisted surface-enhanced Raman scattering (SERS) biosensor for HCC CTCs detection is reported for the first time. The biosensor consists of two basic elements including an anti-ASGPR antibody-Fe3O4@Ag MNPs and an anti-GPC3 antibody-Au@Ag@DTNB NRs. According to the dual-selectivity of the anti-ASGPR and anti-GPC3 antibodies and the dual-enhancement SERS signal of the MNPs silver shell and the Au@Ag NRs SERS tags, a limit of detection of 1 cell/mL for HCC CTC in human peripheral blood samples with a linear relationship from 1 to 100 cells/ mL can be obtained. The system showed good performance in real serum which suggested they would be a promising tool for HCC clinical diagnosis.
      PubDate: 2018-03-09T05:51:36.580975-05:
      DOI: 10.1002/chem.201801133
  • K3B6O9F3: A New Fluorooxoborate with Four Different Anionic Units
    • Authors: Guopeng Han; Guoqiang Shi, Ying Wang, Bingbing Zhang, Shujuan Han, Fangfang Zhang, Zhihua Yang, Shilie Pan
      Abstract: K3B6O9F3, a first fluorooxoborate containing four different units, that is, [BO3]3−, [BO4]5−, [BO3F]4−, and [BO2F2]3−, has been designed and synthesized by two different routes. The unique anionic 2∞[B6O9F3]3− layers avoid forming terminal oxygen atoms, which are beneficial to enlarge the band gap. The structure-properties relationship of the title compound is discussed.Structural diversity: K3B6O9F3, a first fluorooxoborate containing four different units, that is, [BO3]3−, [BO4]5−, [BO3F]4−, and [BO2F2]3−, has been designed and synthesized from two different routes.
      PubDate: 2018-03-09T04:35:36.854811-05:
      DOI: 10.1002/chem.201705751
  • The Pentagonal-Pyramidal Hexamethylbenzene Dication: Many Shades of
           Coordination Chemistry at Carbon
    • Authors: Johannes E. M. N. Klein; Remco W. A. Havenith, Gerald Knizia
      Abstract: A recent report on the crystal structure of the pentagonal-pyramidal hexamethylbenzene dication C6(CH3)62+ by Malischewski and Seppelt [Angew. Chem. Int. Ed. 2017, 56, 368] confirmed the structural proposal made in the first report of this compound in 1973 by Hogeveen and Kwant [Tetrahedron Lett. 1973, 14, 1665]. The widespread attention that this compound quickly gained led us to reinvestigate its electronic structure. On the basis of intrinsic bond orbital analysis, effective oxidation state analysis, ring current analysis, and comparison with well-established coordination complexes, it is demonstrated that the central carbon atom behaves like a transition metal. The central (apical) carbon atom, although best described as a highly Lewis-acidic carbon atom coordinated with an anionic cyclopentadienyl ligand, is also capable of acting as an electron-pair donor to a formal CH3+ group. The different roles of coordination chemistry are discussed.Carbon coordination chemistry: The electronic structure of the pentagonal-pyramidal hexamethylbenzene dication C6(CH3)62+ is investigated through intrinsic bond orbital analysis, effective oxidation state analysis, ring current analysis, and comparison with well-established coordination complexes. The central carbon atom behaves like a transition metal, and incorporates both possible modes of coordination chemistry at carbon, that is, serving as an electron-pair donor and as an electron-pair acceptor, all within a purely hydrocarbon framework.
      PubDate: 2018-03-09T03:46:38.37431-05:0
      DOI: 10.1002/chem.201705812
  • Palladium-Catalyzed Decarboxylative Heck-Type Coupling of Activated
           Aliphatic Carboxylic Acids Enabled by Visible Light
    • Authors: Maximilian Koy; Frederik Sandfort, Adrian Tlahuext-Aca, Linda Quach, Constantin G. Daniliuc, Frank Glorius
      Abstract: The palladium-catalyzed coupling reaction of N-hydroxyphthalimide esters and styrenes to deliver exclusively (E)-substituted olefins under irradiation with visible light is reported. This method tolerates N-hydroxyphthalimide esters derived from primary, secondary, tertiary as well as benzylic carboxylic acids. Notably, Pd(PPh3)4 is employed as an inexpensive palladium source and no addition of base or classical photocatalyst is required. Mechanistic studies suggest a light-mediated single-electron reduction of the activated acid by a photoexcited palladium(0) species to access alkyl radicals through decarboxylation.A palladium-catalyzed coupling reaction of N-hydroxyphthalimide esters and styrenes to deliver (E)-substituted olefins in perfect selectivity under irradiation with visible light is reported. This method tolerates N-hydroxyphthalimide esters derived from primary, secondary, tertiary, and benzylic carboxylic acids, also including complex naturally occurring carboxylic acids. Pd(PPh3)4 is employed as an inexpensive palladium source and no addition of base or classical photocatalyst is required. Mechanistic studies suggest a light-mediated single-electron reduction of the activated acid by a photoexcited palladium(0) species.
      PubDate: 2018-03-09T03:21:19.843176-05:
      DOI: 10.1002/chem.201800813
  • Nanopore Detection of Single-Molecule Binding within a
           Metallosupramolecular Cage
    • Authors: Stefan Borsley; James A. Cooper, Paul J. Lusby, Scott L. Cockroft
      Abstract: Guest encapsulation is a fundamental property of coordination cages. However, there is a paucity of methods capable of quantifying the dynamics of guest binding processes. Here, we demonstrate nanopore detection of single-molecule binding within metallosupramolecular cages. Real-time monitoring of the ion current flowing through a transmembrane α-hemolysin nanopore resolved the binding of different guests to both cage enantiomers. This enabled the single-molecule kinetics of guest binding to be quantified, whereas the ordering and durations of events were consistent with a guest-exchange mechanism that does not involve ligand dissociation. In addition to providing a new approach for single-molecule interrogation of dynamic supramolecular processes, this work also establishes that cage complexes which are too large to enter the nanopore can be exploited for detecting small molecules, thus constituting a new class of molecular adapter.Be my guest: A protein nanopore can resolve both the chirality of individual metallosupramolecular cages, and the dynamics of encapsulation of different guests at the single-molecule level.
      PubDate: 2018-03-09T03:21:08.450369-05:
      DOI: 10.1002/chem.201800760
  • Triarylamine-Cored Dendritic Molecular Gel for Efficient Colorometric,
           Fluorometric, and Impedometeric Detection of Picric Acid
    • Authors: Sanjoy Mondal; Partha Bairi, Sujoy Das, Arun K. Nandi
      Abstract: Detection of nitroaromatics at ultralow concentration is a major security concern in defense, forensics, and environmental science. To this end, a new triarylamine-cored dendritic gelator (OGR) was synthesized, which produced thermoreversible, thixotropic, and fluorescent gels in n-octanol. On gelation, both π–π* transitions and the emission peak of the gelator show redshifts with a 4.5-fold increase of fluorescence intensity in the gel state indicating J-aggregation. The nitrogen lone-pair electrons of OGR make it a donor, and electron transfer occurs to acceptor nitroaromatics causing fluorescence quenching, which is further promoted due to its acidity. The Stern–Volmer rate constants measured for different nitroaromatics showed that it senses picric acid (PA) best. The contact-mode technique with OGR-treated paper strips can allow naked-eye detection of PA under UV light down to 10−11 m concentration within 30 s. Reusability of the gel is achieved by treating OGR@PAx with NaOH solution. Impedance spectroscopic results indicated a decrease of both charge-transport resistance and Warburg impedance on successive addition of PA. The limits of detection of PA determined from fluorescence and impedance measurements match well. Thus, the OGR gel is a reusable, low-cost, specific sensor for PA by naked-eye colorimetric, fluorescence, and impedance techniques.Dendritic gelator: Triarylamine-cored dendritic gelator OGR was synthesized and found to form a thermoreversible, thixotropic, and fluorescent gel in n-octanol. The OGR gel is a reusable, low-cost, specific sensor for picric acid by naked-eye colorimetric (down to 10−11 m), fluorescence, and impedance techniques (see figure).
      PubDate: 2018-03-09T03:05:55.825104-05:
      DOI: 10.1002/chem.201705782
  • Molecular Tectonics with Di- and Trinuclear Organotin Compounds
    • Authors: Irán Rojas-León; Hazem Alnasr, Klaus Jurkschat, María G. Vasquez-Ríos, Irán F. Hernández-Ahuactzi, Herbert Höpfl
      Abstract: Di- and trinuclear organotin(IV) complexes, in which the metal atoms are separated by large aromatic connectors, are useful building blocks for self-assembly. This is demonstrated by the preparation of [1+1], [2+2], and [2+3] macrocyclic and cage-type structures in combination with organic aromatic dicarboxylates. The linkage of the metal atoms by organic binders and the option of varying the number of reactive M−X sites generate versatile building blocks enabling molecular tectonics instead of the node-based strategy generally employed in metallo-supramolecular self-assembly.Tectonic shift: Di- and trinuclear organotin compounds with large aromatic connectors are versatile building blocks for molecular tectonics, as demonstrated by the preparation of [1+1], [2+2], and [2+3] macrocyclic and cage-type structures in combination with organic aromatic dicarboxylates.
      PubDate: 2018-03-09T03:01:08.563326-05:
      DOI: 10.1002/chem.201800791
  • Sensitive and Selective Detection of Phosgene, Diphosgene, and Triphosgene
           by a 3,4-Diaminonaphthalimide in Solutions and the Gas Phase
    • Authors: Shao-Lin Wang; Lin Zhong, Qin-Hua Song
      Abstract: Phosgene and its substitutes, diphosgene and triphosgene, are highly toxic and widely used chemicals, so it is necessary to investigate their reactivity and develop facile, sensitive, and specific methods for detecting them. In this work, we have developed a new 1,8-naphthalimide-based fluorescent chemosensor, Phos-2, which exhibits high sensitivity (detection limits: 0.2–0.7 nm), high selectivity to phosgene and its substitutes over nitric oxide (NO), various acyl chlorides, and nerve agent mimics in solutions. Based on investigation of the reaction kinetics of Phos-2 with phosgene and its substitutes, a two-step sensing mechanism was clarified. The second-order rate constants (k2) of Phos-2 reveal that the relative rate constants of phosgene, diphosgene, and triphosgene are 40:4:1. Moreover, a Phos-2 test paper has been fabricated as a low-cost, sensitive (≈5 ppm from observation by the naked eye or 0.1 ppm from a measurement), and efficient method for visual detection of a low concentration of phosgene in the gas phase.Detecting phosgene: A highly sensitive fluorescent chemosensor, Phos-2, was developed for the selective detection of phosgene and its substitutes over nitric oxide, various acyl chlorides, and nerve agent mimics. A two-step sensing mechanism was clarified from the kinetics of the sensing reaction. A portable test paper with Phos-2 was fabricated for sensitive and selective detection of phosgene in the gas phase.
      PubDate: 2018-03-09T03:00:58.00479-05:0
      DOI: 10.1002/chem.201800051
  • A Total Synthesis of Salinosporamide A
    • Authors: Léo B. Marx; Jonathan W. Burton
      Abstract: Salinosporamide A is a β-lactone proteasome inhibitor currently in clinical trials for the treatment of multiple-myeloma. Herein we report a short synthesis of this small, highly functionalized, biologically important natural product that uses an oxidative radical cyclization as a key step and allows for the preparation of gram quantities of advanced synthetic intermediates.A scalable total synthesis of the potent proteasome inhibitor salinosporamide A is reported that proceeds in 16 steps and 5 % overall yield and features an oxidative radical cyclization as a key step.
      PubDate: 2018-03-09T03:00:47.785644-05:
      DOI: 10.1002/chem.201800046
  • Dianionic Carbon-Bridged Scandium–Copper/Silver Heterobimetallic
           Complexes: Synthesis, Bonding, and Reactivity
    • Authors: Chen Wang; Li Xiang, Yan Yang, Jian Fang, Laurent Maron, Xuebing Leng, Yaofeng Chen
      Abstract: Alkylidene-bridged scandium–copper/silver heterobimetallic complexes were synthesized and structurally characterized. The complexes contain different Sc−C and M−C (M=CuI, AgI) bonds. The reactivity of the scandium–copper heterobimetallic complex was also studied, which reveals that the heterobimetallic complex is a reaction intermediate for the transmetalation of akylidene group from ScIII to CuI. The scandium–copper heterobimetallic complex also undergoes an addition reaction with CO, resulting in the formation of a new C=C double bond. DFT calculations were used to study the bonding and the subsequent reactivity with CO of the scandium–copper heterobimetallic complex. It clearly demonstrates a cooperative effect between the two metal centers through the formation of a direct Sc⋅⋅⋅Cu interaction that drives the reactivity with CO.Different places: Alkylidene-bridged Sc–Cu/Ag heterobimetallic complexes were synthesized and structurally characterized. The Sc–Cu heterobimetallic complex reacts with CuI, isocyanide, or CO and a cooperative effect between the two metal centers through the formation of a direct Sc⋅⋅⋅Cu interaction was demonstrated for the CO insertion reaction (see scheme).
      PubDate: 2018-03-09T03:00:39.549103-05:
      DOI: 10.1002/chem.201706147
  • Recent Advances in Multi-component Particles Assembly
    • Authors: Dan Guo; Yanlin Song
      Abstract: Particles assembly and co-assembly have been research frontiers in chemistry and material science in the past few decades. To achieve a large variety of intricate structures and functional materials, remarkable progress has been made in the particle assembly principles and strategies. It can be summarized that the particle assembly is driven by intrinsic interparticle interaction or the external control. In this article, we focus on binary or ternary particles co-assembly and review the principles and feasible strategies. These advances have led to new disciplines of microfabrication technology and material engineering. Although remarked achievement on particle-based structures has been made, it is still challenging to fully develop general and facile strategies to precisely control the one-dimensional (1D) co-assembly. This article reviews the recent development on multi-component particles co-assembly, which significantly increases structural complexity and functional diversity. In particular, we highlight the advances in the particles co-assembly of well-ordered 1D binary superstructures by liquid soft confinement. Finally, prospective outlook for future trends in this field is proposed.
      PubDate: 2018-03-09T02:45:26.413281-05:
      DOI: 10.1002/chem.201800264
  • One-Dimensional Porphyrin-Fullerene (C60) Assemblies: Role of Central
           Metal Ion in Enhancing Ambipolar Mobility
    • Authors: Goudappagouda - -; Murali - Gedda, Giridhar U. Kulkarni, Santhosh Babu Sukumaran
      Abstract: One-dimensional (1D) nanostructures of -conjugated molecules exhibiting excellent charge carrier mobilities have found much interest in organic electronic devices. Even though it is tedious to form such structures, the availability of highly delocalized electron and hole carriers in these donor (D)-acceptor (A) co-assemblies realize ambipolar charge transport. Here we report the successful demonstration of a simple solution casting method to create ambipolar donor-acceptor single crystalline assembly. 1D assemblies of 5,10,15,20-tetraphenylporphyrins (H2TPP, ZnTPP) and fullerene (C60) exhibit high ambipolar mobility in the range of 0.8-3.4 cm2/Vs for electrons and holes with high ON/OFF ratio and low threshold voltage. A direct experimental proof for the pivotal role of central Zn2+ in tetraphenyl porphyrin, which enables a strong D-A charge transfer interaction in the cocrystal and thereby induces electron (1.35 cm2/Vs), hole (3.42 cm2/Vs) mobilities, the highest reported for two component D-A assemblies using solution casting, is demonstrated.
      PubDate: 2018-03-09T00:50:47.373371-05:
      DOI: 10.1002/chem.201800197
  • Density Functional Theory simulations of water adsorption and activation
           on the (-201) β-Ga2O3 surface
    • Authors: roozbeh anvari; Dino Spagnoli, Giacinta Parish, Brett Nener
      Abstract: Density functional theory (DFT) calculations are used to study the molecular and dissociative adsorption of water on the (-201) β-Ga2O3 surface. The effect of adsorption of different water-like species on geometry, binding energies, vibrational spectra and the electronic structure of the surface are discussed. The study shows that while the hydrogen evolution reaction requires a small amount of energy to become energetically favourable, the over-potential for activating the oxygen evolution reaction is quite high. The results of our calculations provide insight as to why a high voltage is required in experiments to activate the water-splitting reaction, while previous studies of gallium oxide predicted very low activation energies for other energetically more favourable facets. Application of this work to studies of GaN-based chemical sensors with gallium oxide surface shows it is possible to select the gate bias so that the sensors are not influenced by water splitting reactions. It was also found that in the region where water-splitting does not occur, the surface can exist in two states: water or hydroxyl terminated.
      PubDate: 2018-03-09T00:15:21.955946-05:
      DOI: 10.1002/chem.201706175
  • An Alumino-Mannich Reaction of Organoaluminum Reagents, Silylated Amines,
           and Aldehydes
    • Authors: Anika Tarasewicz; Deeba Ensan, Robert Alexander Batey
      Abstract: A multi-component coupling using organoaluminum reagents, silylated amines, and aldehydes results in the formation of tertiary amines. Both alkenyl and alkyl organoaluminum reagents undergo reaction with iminium ion substrates for which the corresponding Petasis borono-Mannich reactions are unsuccessful.
      PubDate: 2018-03-08T15:51:09.540085-05:
      DOI: 10.1002/chem.201801012
  • Electronic Transmutation (ET): Chemically Turning One Element into Another
    • Authors: Xinxing Zhang; Katie Lundell, Jared Olson, Alexander Boldyrev, Kit H. Bowen
      Abstract: The concept of electronic transmutation (ET) depicts the processes that by acquiring an extra electron, an element with the atomic number Z begins to have properties that were known to only belong to its neighboring element with the atomic number Z+1. Based on ET, signature compounds and chemical bonds that are composed of certain elements can now be designed and formed by other electronically transmutated elements. This minireview summarizes the recent developments and applications of ET on both the theoretical and experimental fronts. Examples on the ET of Group 13 elements into Group 14 elements, Group 14 elements into Group 15 elements, and Group 15 elements into Group 16 elements are discussed. Compounds and chemical bonding composed of carbon, silicon, germanium, phosphorous, oxygen and sulfur now have analogs using transmutated boron, aluminum, gallium, silicon, nitrogen and phosphorous.
      PubDate: 2018-03-08T14:45:26.964416-05:
      DOI: 10.1002/chem.201800517
  • Oligonucleotide length dependent formation of virus-like particles
    • Authors: stan J. Maassen; Mark Vincent de Ruiter, Saskia Lindhoud, Jeroen J.L.M. Cornelissen
      Abstract: Understanding the assembly pathway of viruses can contribute to creating monodisperse virus-based materials. In this study the Cowpea Chlorotic Mottle Virus is used to determine the interactions between the capsid proteins of viruses and their cargo. The assembly of the capsid proteins in the presence of different lengths of short single-stranded DNA is studied at neutral pH, where the protein-protein interactions are weak. Chromatography, electrophoresis, microscopy, and light scattering shows that the assembly efficiency and speed of the particles increases with increasing length of oligonucleotides. The minimal length required for assembly at the conditions used here is shown to be 14 nucleotides. Assembly of particles containing such short strands of ssDNA can take almost a month. This slow assembly process enabled the study of intermediate states, confirming a low cooperative assembly for CCMV and allows for further expansion of current assembly theories.
      PubDate: 2018-03-08T12:27:27.832312-05:
      DOI: 10.1002/chem.201800285
  • An unprecedented retro-Mumm rearrangement revealed by ESI-MS/MS, IRMPD
           spectroscopy, and DFT calculations
    • Authors: Claudio Iacobucci; Samantha Reale, Massimiliano Aschi, Jos Oomens, Giel Berden, Francesco De Angelis
      Abstract: Brønsted acids and protic solvents mediate acyl transfer, known as Mumm rearrangement, from imidates to the corresponding acylamides. This represents a key step in several reactions, e.g. the Ugi-four component reaction (U-4CR) and Passerini-three component reaction (P-3CR). Herein we report an unprecedented break of the non-reversibility of the Mumm rearrangement. A combination of electrospray tandem mass spectrometry (ESI-MS/MS), infrared multiphoton dissociation (IRMPD) ion spectroscopy and theoretical calculations demonstrates the occurrence of the retro-Mumm rearrangement of protonated isopeptides in the gas-phase. In the gas-phase, the extra proton acquired in the electrospray ionisation promotes in a catalytic fashion the backward isomerisation reaction.
      PubDate: 2018-03-08T10:15:25.830167-05:
      DOI: 10.1002/chem.201800347
  • From Mesocates to Helicates: Nickel(II) Supramolecular Assemblies Derived
           from Tetradentate Schiff Bases. Structural, Magnetic and Chiro-Optical
    • Authors: Albert Escuer; Julia Mayans, Lorenzo Di Bari, Merce Font-Bardia, Lorenzo Arrico, Francesco Zinna, Gennaro Pescitelli
      Abstract: The systematic reactions of a family of tetradentate pyridyl/imine and quinolyl/imine racemic or enantiopure Schiff bases with Ni(NO3)2 or Ni(ClO4)2 in the presence of sodium azide yielded, as a function of the starting racemic, chiral or achiral base, a set of chiral, meso or achiral complexes. In all cases, the compounds consist in two NiII cations linked by a double azido bridge in its end-on coordination mode. All the dimers exhibit a mesocate supramolecular structure and one of them, the unprecedented mix of helicate and mesocate in 2:1 ratio. The transition from mesocate to helicate conformation has been reached tuning the flexibility of the central spacers of the Schiff bases and the size of the substituents. Electronic circular dichroism (ECD) studies have been performed for two pairs of enantiomers and interpreted by means of DFT calculations. Susceptibility measurements show a ferromagnetic coupling between the Ni(II) cations mediated by the end-on azido bridges.
      PubDate: 2018-03-08T09:42:21.462755-05:
      DOI: 10.1002/chem.201800323
  • Mechanism of Ultrafast Intersystem Crossing in 2-Nitronaphthalene
    • Authors: J. Patrick Zobel; Juan J. Nogueira, Leticia González
      Abstract: Nitronaphthalene derivatives efficiently populate their electronically excited triplet states upon photoexcitation through ultrafast intersystem crossing (ISC). Despite having been studied extensively by time-resolved spectroscopy, the reasons behind their ultrafast ISC remain unknown. Herein, we present the first ab initio nonadiabatic molecular dynamics study of a nitronaphthalene derivative, 2-nitronaphthalene, including singlet and triplet states. We find that there are two distinct ISC reaction pathways involving different electronic states at distinct nuclear configurations. The high ISC efficiency is explained by the very small electronic and nuclear alterations that the chromophore needs to undergo during the singlet–triplet transition in the dominating ISC pathway after initial dynamics in the singlet manifold. The insights gained in this work are expected to shed new light on the photochemistry of other nitro polycyclic aromatic hydrocarbons that exhibit ultrafast intersystem crossing.(Not So) ultrafast: Non-adiabatic dynamics discover a new mechanism for the excited-state deactivation of 2-nitronaphthalene including multiple intersystem crossing pathways. It is shown that intersystem crossing does occur on a ps time scale and thus not as ultrafast as previously experimentally reported (see figure).
      PubDate: 2018-03-08T09:05:50.221099-05:
      DOI: 10.1002/chem.201705854
  • Organotin Dyes Bearing Anionic Boron Clusters as Cell-Staining Fluorescent
    • Authors: Blanca M. Muñoz-Flores; Justo Cabrera-González, Clara Viñas, Arturo Chávez-Reyes, H. V. Rasika Dias, Víctor M. Jiménez-Pérez, Rosario Núñez
      Abstract: Within the cell nucleus, in the nucleoli, ribosomal RNAs are synthesized and participate in several biological processes. To better understand nucleoli-related processes, their visualization is often required, for which specific markers are needed. Herein, we report the design of novel fluorescent organotin compounds derived from 4-hydroxy-N′-((2-hydroxynaphthalen-1-yl)methylene)benzohydrazide and their cytoplasm and nucleoli staining of B16F10 cells in vitro. Tin compounds bearing an aliphatic carbon chain (-C12H25) and an electron-donating group (-OH) were prepared, and the latter could be derivatized to bear the boron cluster anions [B12H12]2− and [3,3′-Co(1,2-C2B9H11)2]− (COSAN). All of the conjugates have been fully characterized and their luminescence properties have been assessed. In general, they show good quantum yields in solution (24–49 %), those for the COSAN derivatives being lower. Remarkably, the linking of [B12H12]2− and COSAN to the complexes made them more soluble, without being detrimental to their luminescence properties. Living B16F10 cells were treated with all of the compounds to determine their fluorescence staining properties; the compounds bearing the aliphatic chain showed a reduced staining capacity due to the formation of aggregates. Notably, the complexes bearing different boron clusters showed different staining effects; those bearing [B12H12]2− showed extraordinary staining of the nucleoli and cytoplasm, whereas those bearing COSAN were only detected in the cytoplasm. The remarkable fluorescence staining properties shown by these organotin compounds make them excellent candidates for fluorescence bioimaging in vitro.Selective cell staining: The design of fluorescent organotin compounds derived from 4-hydroxy-N′-((2-hydroxynaphthalen-1-yl)methylene)benzohydrazidato and their cell staining in vitro are described. Compounds bearing [B12H12]2− show extraordinary staining of nucleoli and cytoplasm, whereas the COSAN-containing dyes only stain cytoplasm. The remarkable fluorescent staining properties shown by these compounds make them excellent candidates as cell-staining fluorescent probes.
      PubDate: 2018-03-08T09:03:22.865613-05:
      DOI: 10.1002/chem.201705804
  • Microwave-Assisted, Asymmetric Synthesis of 3-Amino-2,3-Dihydrobenzofuran
           Flavonoid Derivatives from Chalcones
    • Authors: Travis R. Helgren; Lianyan L. Xu, Daniel Sotelo, Yash R. Mehta, Melissa A. Korkmaz, Ivan Pavlinov, Leslie N. Aldrich
      Abstract: A route to access 3-amino-2,3-dihydrobenzofurans that utilizes microwave-assisted organic synthesis to rapidly generate analogues has been developed. The route begins with an acid-catalyzed, microwave-assisted aldol condensation to generate chalcone intermediates, followed by a Corey–Bakshi–Shibata reduction and subsequent Sharpless asymmetric epoxidation to access stereoisomeric epoxyalcohols. The final step is a one-pot, microwave-assisted, regioselective, acid-catalyzed epoxide opening with various amines followed by an intramolecular nucleophilic aromatic substitution reaction to generate the 3-amino-2,3-dihydrobenzofurans. This route provides ready access to stereochemically and structurally diverse analogues of these flavonoid scaffolds. Additionally, a pilot library was synthesized, and the biological activity diversity of the chalcones and dihydrobenzofurans was explored in human carcinoma cell lines.Microwave-assisted reactions enable rapid access to benzofuran scaffolds with stereochemical and structural diversity, which leads to biological performance diversity. A one-pot, regioselective, acid-catalyzed epoxide opening followed by an intramolecular nucleophilic aromatic substitution reaction provides 3-amino-2,3-dihydrobenzofurans from epoxyalcohols in 30–70 minutes.
      PubDate: 2018-03-08T08:11:01.935452-05:
      DOI: 10.1002/chem.201705984
  • Three-Component Domino Knoevenagel/Vinylogous Michael Reaction: Entry to
           Challenging o-Terphenyls
    • Authors: Dominik Grau; Benedikt W. Grau, Frank Hampel, Svetlana B. Tsogoeva
      Abstract: An unprecedented organocatalytic three-component domino Knoevenagel/vinylogous Michael reaction starting from simple enolizable aldehydes, malononitrile, and nitroolefins is reported. This facile two-step domino process provides a straightforward stereoselective route to multifunctional vinyl malononitrile products (up to 82 % yield, 85:15 d.r.) containing a nitroalkane moiety, and contributes to the development of sustainability and atom economy. The application of the obtained domino products for synthesis of highly functionalized o-terphenyls (of high interest for materials science and medicinal chemistry) through subsequent new three-step domino reaction involving cyclization–tautomerization–aromatization steps, has been demonstrated.All-in-one synthesis: An unprecedented three-component domino Knoevenagel/vinylogous Michael reaction, providing a straightforward diastereoselective route to multifunctional vinyl malononitrile products is presented (see scheme). The applications of the new domino products for facile synthesis of highly functionalized o-terphenyls through a subsequent new three-step linear domino process, has been demonstrated.
      PubDate: 2018-03-08T08:10:43.512754-05:
      DOI: 10.1002/chem.201800048
  • Nickel-Catalyzed Alkylarylation of Activated Alkenes with Benzylamines via
           C-N Bond Activation
    • Authors: Hanmin Huang; Hui Yu, Bin Hu
      Abstract: A nickel-catalyzed alkylarylation of active alkenes with tertiary benzylamines was achieved via charge-transfer complex promoted C-N bond activation. The reaction proceeds through initial Ni-catalyzed C-N bond activation, followed by sequential radical addition, redox and proton-abstraction with cleaved amine-moiety in the absence of oxidant, which provides an efficient method to prepare various alkyl-substituted oxindoles and dihydroquinolinones in good yields.
      PubDate: 2018-03-08T07:25:46.581938-05:
      DOI: 10.1002/chem.201800543
  • Advances in cell scaffolds for tissue engineering: the value of liquid
           crystalline elastomers
    • Authors: Daniele Martella; Camilla Parmeggiani
      Abstract: Recent discoveries evidenced that many cells organize into well-aligned nematic domains, showing also their topological defects and suggesting the liquid crystalline order to be necessary for some biological functions. These evidences were described as the basis for the development of a new area of research in which polymeric liquid crystals were developed to exploit and promote cell adhesion and proliferation towards tissue regeneration. To address the requirements of tissue engineering, the new biocompatible materials have to be designed and synthesized to support cell adherence and growth together with nutrient transport under physiological condition. This review presents a journey that, starting from the first discovery of liquid crystalline phases in biological (natural) materials with different structures and physical-chemical properties, will drive the readers towards the very recent application of liquid crystal polymeric materials as functional cell scaffolds addressing current tissue engineering issues.
      PubDate: 2018-03-08T06:15:29.37956-05:0
      DOI: 10.1002/chem.201800477
  • Crystal Field in Rare-Earth Complexes: From Electrostatics to Bonding
    • Authors: Riccardo Alessandri; Habiburrahman Zulfikri, Jochen Autschbach, Hélène Bolvin
      Abstract: The flexibility of first-principles (ab initio) calculations with the SO-CASSCF (complete active space self-consistent field theory with a treatment of the spin-orbit (SO) coupling by state interaction) method is used to quantify the electrostatic and covalent contributions to crystal field parameters. Two types of systems are chosen for illustration: 1) The ionic and experimentally well-characterized PrCl3 crystal; this study permits a revisitation of the partition of contributions proposed in the early days of crystal field theory; and 2) a series of sandwich molecules [Ln(ηn-CnHn)2]q, with Ln=Dy, Ho, Er, and Tm and n=5, 6, and 8, in which the interaction between LnIII and the aromatic ligands is more difficult to describe within an electrostatic approach. It is shown that a model with three layers of charges reproduces the electrostatic field generated by the ligands and that the covalency plays a qualitative role. The one-electron character of crystal field theory is discussed and shown to be valuable, although it is not completely quantitative. This permits a reduction of the many-electron problem to a discussion of the energy of the seven 4f orbitals.Separating key components: The flexibility of first-principles (ab initio) calculations is used to quantify the electrostatic and covalent contributions to crystal field parameters for a selection of rare-earth complexes. The one-electron character of crystal field theory is discussed and, although valuable, it is not completely quantitative. This permits a reduction of the many-electron problem to a discussion of the energy of the seven 4f orbitals
      PubDate: 2018-03-08T06:05:10.117463-05:
      DOI: 10.1002/chem.201705748
  • Fast and Selective Heavy Metal Removal by a Novel Metal-Organic Framework
           Designed with In-Situ Ligand Building Block Fabrication Bearing Free
    • Authors: Farzaneh Rouhani; Ali Morsali
      Abstract: Fast and effective adsorbents for the selective removal of HgII and PbII ions were prepared by the reaction of Zn(NO3)2⋅6H2O, H2BDC, and N1,N2-bis(pyridin-4-ylmethylene) ethane-1,2-diamine (L) that yields an unprecedented two-dimensional layer-based supramolecular framework, {Zn(BDC)(L*)}⋅DMF (TMU-40), by solvothermal reaction. The formation of this framework involved an in situ C=C coupling of L to L* [L*=5,6-di(pyridin-4-yl)-1,2,3,4-tetrahydropyrazine]. As L* contains free nitrogen atoms, direct reaction of L* and metals led to metallated products. Post-synthetic modification of this novel MOF (TMU-40) with H2O2 gives a new framework (O-TMU-40) by same structure and different ligand, which also bears free nitrogen atoms. FTIR spectra, TGA analysis, X-ray diffraction, Zeta Potential analysis and 1H NMR spectroscopy were used to characterize the prepared frameworks. The TMU-40 and O-TMU-40 frameworks were used for heavy-metal removal from aqueous solutions. Maximum adsorption values of 269 mg g−1 for HgII with TMU-40 and 215 mg g−1 for PbII with O-TMU-40 were achieved in 10 min at 298 Kwithout changes in the pH of the adsorption medium with pseudo-second order kinetics based on the Langmuir model. The extremely fast kinetics of TMU-40 means this adsorbent can reduce heavily contaminated water containing HgII concentrations of 40 ppm down to the acceptable limit of 2 ppb.Heavy metal in the MOF pit: Fast and effective adsorbents for selective removal of HgII and PbII ions were prepared by the solvothermal reaction of Zn(NO3)2⋅6H2O, H2BDC and N1,N2-bis(pyridin-4-ylmethylene) ethane-1,2-diamine (L) that yields an unprecedented two-dimensional layer-based supramolecular framework, {Zn(BDC)(L*)}⋅DMF (TMU-40). Post-synthetic modification with H2O2 results in new framework O-TMU-40 also bearing free nitrogen atoms available for mercury and lead adsorption.
      PubDate: 2018-03-08T05:26:55.394045-05:
      DOI: 10.1002/chem.201706016
  • Spacer Length-Independent Shuttling of the Pillar[5]arene Ring in Neutral
    • Authors: Tomoki Ogoshi; Daisuke Kotera, Shungo Nishida, Takahiro Kakuta, Tada-aki Yamagishi, Albert M. Brouwer
      Abstract: For a series of neutral [2]rotaxanes consisting of a pillar[5]arene ring and axles possessing two stations separated by flexible spacers of different lengths, the free energies of activation for the ring shuttling between the stations were found to be independent of the spacer length. The constitution of the spacer affects the activation energies: replacement of CH2 groups by repulsive oxygen atoms in the axle increases the barrier. The explanation for the observed length-independence lies in the presence of a barrier for re-forming the stable co-conformation, which makes the ring travel back and forth along the thread in an intermediate state.Molecular dynamics: The ring-shuttling rate between two stations in neutral pillar[5]arene-based [2]rotaxanes is independent of the length of spacers connecting the two stations. The explanation for the observed length independence lies in the presence of a barrier for re-forming the stable co-conformation, which makes the ring travel back and forth along the thread in an intermediate state (see scheme).
      PubDate: 2018-03-08T05:26:44.695433-05:
      DOI: 10.1002/chem.201800104
  • Anisotropic Thermal and Guest-Induced Responses of an Ultramicroporous
           Framework with Rigid Linkers
    • Authors: Josie E. Auckett; Samuel G. Duyker, Ekaterina I. Izgorodina, Chris S. Hawes, David R. Turner, Stuart R. Batten, Vanessa K. Peterson
      Abstract: The interdependent effects of temperature and guest uptake on the structure of the ultramicroporous metal–organic framework [Cu3(cdm)4] (cdm=C(CN)2(CONH2)−) were explored in detail by using in situ neutron scattering and density functional theory calculations. The tetragonal lattice displays an anisotropic thermal response related to a hinged “lattice-fence” mechanism, unusual for this topology, which is facilitated by pivoting of the rigid cdm anion about the Cu nodes. Calculated pore-size metrics clearly illustrate the potential for temperature-mediated adsorption in ultramicroporous frameworks due to thermal fluctuations of the pore diameter near the value of the target guest kinetic diameter, though in [Cu3(cdm)4] this is counteracted by a competing contraction of the pore with increasing temperature as a result of the anisotropic lattice response.The metal–organic framework [Cu3(cdm)4] exhibits areal negative thermal expansion over a broad temperature range. In situ neutron scattering and DFT calculations provided considerable insight into the underlying atomistic causes of this phenomenon, the influence of adsorbed guest molecules, and the implications for potential temperature-mediated adsorption in ultramicroporous frameworks (see figure).
      PubDate: 2018-03-08T05:26:32.605886-05:
      DOI: 10.1002/chem.201800261
  • Visiting the Limits between a Highly Strained 1-Zirconacyclobuta-2,3-diene
           and Chemically Robust Dizirconacyclooctatetraene
    • Authors: Fabian Reiß; Melanie Reiß, Anke Spannenberg, Haijun Jiao, Wolfgang Baumann, Perdita Arndt, Uwe Rosenthal, Torsten Beweries
      Abstract: The reaction of the allene precursor Li2(Me3SiC3SiMe3) with [Cp2ZrCl2] (Cp=cyclopentadienyl) was examined. The selective formation of hitherto unknown linear, allene-bridged dizirconocene complexes [(Cp2ZrCl)2{−μ-(Me3Si)C3(SiMe3)−}] and [(Cp2Zr)2{−μ-(Me3Si)C3(SiMe3)−}2] was observed. Upon σ coordination of the allenediyl unit to {Cp2Zr}, pyrophoric Li2(Me3SiC3SiMe3) is tamed stepwise to yield a surprisingly robust 1,5-dizirconacyclooctatetra-2,3,6,7-ene with cumulated double bonds. This complex is unexpectedly inert against moisture, air, water and acetone. Surprisingly, it degrades under MS conditions to give the highly strained 1-zirconacyclobuta-2,3-diene. All compounds isolated have been fully characterised and the molecular structures are discussed. The stability and reactivity of these complexes are rationalised by DFT computations.The taming of a shrew: The reaction of a pyrophoric dilithioallene with zirconocene results in remarkable stabilisation and the stepwise formation of a highly unusual dizirconacyclooctatetraene species (see Scheme).
      PubDate: 2018-03-08T05:23:53.000248-05:
      DOI: 10.1002/chem.201800465
  • Interrogating Protein Phosphatases with Chemical Activity Probes
    • Authors: Garrett R. Casey; Cliff I. Stains
      Abstract: Protein phosphatases, while long overlooked, have recently become appreciated as drivers of both normal- and disease-associated signaling events. As a result, the spotlight is now turning torwards this enzyme family and efforts geared towards the development of modern chemical tools for studying these enzymes are well underway. This Minireview focuses on the evolution of chemical activity probes, both optical and covalent, for the study of protein phosphatases. Small-molecule probes, global monitoring of phosphatase activity through the use of covalent modifiers, and targeted fluorescence-based activity probes are discussed. We conclude with an overview of open questions in the field and highlight the potential impact of chemical tools for studying protein phosphatases.Illuminating Protein Phosphatases: Protein phosphatases are becoming recognized as critical signaling enzymes in both normal and disease physiology. Chemical reporters of enzymatic activity are poised to provide insights into the chemical biology of these important signaling enzymes.
      PubDate: 2018-03-08T05:23:44.834238-05:
      DOI: 10.1002/chem.201705194
  • Regioselective C−H Alkylation via Carboxylate-Directed
           Hydroarylation in Water
    • Authors: Guodong Zhang; Fan Jia, Lukas J. Gooßen
      Abstract: In the presence of catalytic [RuCl2(p-cym)]2 and using Li3PO4 as the base, benzoic acids react with olefins in water to afford the corresponding 2-alkylbenzoic acids in moderate to excellent yields. This C−H alkylation process is generally applicable to diversely substituted electron-rich and electron-deficient benzoic acids, along with α,β-unsaturated olefins including unprotected acrylic acid. The widely available carboxylate directing group can be removed or utilized for further derivatization. Mechanistic investigations revealed that the transformation proceeds via a ruthenacycle intermediate.Water serves as the solvent in a regioselective ortho-C−H alkylation of arenecarboxylates with α,β-unsaturated olefins catalyzed by ruthenium. A wide range of arene substrates are converted efficiently and the weakly basic medium allows the use of even unprotected acrylic acid as an alkyl source.
      PubDate: 2018-03-08T05:23:34.339746-05:
      DOI: 10.1002/chem.201800757
  • Promotion of a Reaction by Cooling: Stereoselective
           1,2-cis-α-Thioglycoconjugation by Thiol-Ene Coupling at −80 °C
    • Authors: Dániel Eszenyi; Viktor Kelemen, Fanny Balogh, Miklós Bege, Magdolna Csávás, Pál Herczegh, Anikó Borbás
      Abstract: The photoinitiated thiol-ene coupling reactions of 2-substituted glycals were studied as a generally applicable strategy for stereoselective 1,2-cis-α-thioconjugation. Although all glycals reacted with full α-selectivity, the efficacy of the reactions varied in a broad range depending on their configuration and glycals bearing axial acetoxy substituents reacted with very low efficacy at room temperature. The study revealed that the reaction progress could be promoted by cooling and inhibited by heating. At −80 °C, the equilibrium of the rapidly reversible addition of the thiyl radical to alkenes is shifted almost completely toward products, leading to efficient addition reactions. By exploiting this unique temperature effect a series of α-thio-l-fucosides, -d-galactosides, and d-GlcNAc derivatives were prepared with high efficacy and complete stereoselectivity.Sulfur sugars: Reaction temperature influences the thiol-ene reactions of cyclic alkenes in a very unique fashion: cooling promotes whereas heating inhibits the reaction. Unfavorable steric and electronic effects resulting in low conversions at room temperature were overcome by conducting the reactions at −80 °C. The thiol-ene coupling reaction of 2-substituted hexoglycals at −80 °C is an efficient strategy for stereoselective 1,2-cis-α-thioconjugation.
      PubDate: 2018-03-08T05:23:26.264706-05:
      DOI: 10.1002/chem.201800668
  • Controlling Selectivity in Aliphatic C−H Oxidation through
           Supramolecular Recognition
    • Authors: Diego Vidal; Giorgio Olivo, Miquel Costas
      Abstract: Aliphatic C−H oxidation is the most straightforward approach to functionalize hydrocarbon skeletons. The main challenge of this reaction is the control of site selectivity, given the multiple C−H bonds present in any organic molecule. Natural enzymes elegantly solve this problem through the interplay of different interactions that geometrically orient the substrate to expose a single C−H bond to the active unit, thus overriding intrinsic reactivity patterns. A combination of molecular catalysts and supramolecular receptors can be a promising way to replicate such control. This strategy indeed unlocks hydroxylation of C−H bonds that are not accessible with conventional methodologies, in which the selectivity is dictated by the geometry of the substrate–receptor adduct. Herein, we review the reports of recognition-driven C−H oxidation reactions and highlight the key design principles that inspired these works.The use of supramolecular interactions to bind and orient the substrate can unlock novel selectivities in C−H oxidation. In this Minireview different, bioinspired strategies towards this goal are discussed.
      PubDate: 2018-03-08T05:23:14.18145-05:0
      DOI: 10.1002/chem.201704852
  • Toward High-Performance Vacuum-Deposited OLEDs: Sublimable Cationic
           Iridium(III) Complexes with Yellow and Orange Electroluminescence
    • Authors: Dongxin Ma; Chen Zhang, Ruihuan Liu, Yong Qiu, Lian Duan
      Abstract: Great advances in the development of efficient luminescent materials are the driving force behind organic light-emitting diodes (OLEDs). Sublimable ionic transition-metal complexes (iTMCs) have emerged as a large family of new emissive dopants applied for vacuum-deposited OLEDs, while the achievement of excellent performance remains arduous. A series of novel sublimable cationic iridium(III) complexes have been designed and synthesized, containing an imidazole-type ancillary ligand and tetraphenylborate-type negative counter-ions with large steric hindrance and well-dispersed charges. The photophysical properties, electrochemical behaviors, and thermal stability are fully investigated and discussed, then demonstrated by theoretical calculations. Yellow- and orange-emitting OLEDs thereof are fabricated by vacuum evaporation deposition, realizing a high external quantum efficiency of up to 11 %, maximum brightness over 27.3×103 cd m−2 and low turn-on voltages below 2.4 V, among the best results of analogous phosphorescent OLEDs based on iTMCs. This work indicates the promising applications of sublimable iTMCs in state-of-the-art vacuum-deposited optoelectronic devices.A series of sublimable cationic iridium(III) complexes are designed, synthesized, investigated, and applied as yellow and orange emitters for vacuum-deposited OLEDs, achieving a high EQE up to 11 %, maximum brightness over 27.3×103 cd m−2 and turn-on voltages below 2.4 V.
      PubDate: 2018-03-08T05:22:05.414274-05:
      DOI: 10.1002/chem.201705559
  • Solvent and autocatalytic effects on the stabilization of the σ-complex
           during electrophilic aromatic chlorination.
    • Authors: Ruben Van Lommel; Samuel L. C. Moors, Frank De Proft
      Abstract: The solvent and autocatalytic effects of the electrophilic aromatic chlorination of benzene are studied using a combined approach of static calculations and ab initio metadynamics simulations. Different possible reaction pathways are investigated and the influence of the solvent (CCl4, acetonitrile and acetic acid) is thoroughly assessed. Our results show that the stability and lifetime of a charged σ-complex is increased by electrostatic stabilization effects of the environment, which can originate from catalytic HCl, solvating effects of polar solvents (acetonitrile), or specific hydrogen bonding interactions with the solvent (acetic acid). Metadynamics simulations reveal a new chlorine addition mechanism explaining the autocatalytic effects of the reaction. We highlight the strength of combining static calculations and metadynamics simulations, which provide complementary insight into chemical reactions in solvent.
      PubDate: 2018-03-08T04:45:23.859224-05:
      DOI: 10.1002/chem.201800385
  • Formal Lossen Rearrangement/[3+2] Annulation Cascade Catalyzed by a
           Modified Cyclopentadienyl RhIII Complex
    • Authors: Takayuki Yamada; Yu Shibata, Susumu Kawauchi, Soichi Yoshizaki, Ken Tanaka
      Abstract: It has been established that a cyclopentadienyl RhIII complex with two phenyl groups and a pendant amide moiety catalyzes the formal Lossen rearrangement/[3+2] annulation cascade of N-pivaloyl benzamides and acrylamides with alkynes leading to substituted indoles and pyrroles. Mechanistic studies revealed that this cascade reaction proceeds via not the Lossen rearrangement to form anilides or enamides but C-H bond cleavage, alkyne insertion, and the formal Lossen rearrangement.
      PubDate: 2018-03-07T22:45:39.596733-05:
      DOI: 10.1002/chem.201801125
  • Fluorescence Redox Blinking Adaptable to Structural Analysis of Nucleic
    • Authors: Takafumi Miyata; Naohiko Shimada, Atsushi Maruyama, Kiyohiko Kawai
      Abstract: The phenomenon of blinking is unique to single-molecule fluorescence measurements. By designing a fluorophore with an appropriate dark-state lifetime τoff, a kinetic analysis based on the control of fluorescence blinking (KACB) was devised to investigate the dynamics of biomolecules. By controlling the redox-reaction-based blinking (rKACB), conformational dynamics of RNA at the single-molecule level was previously investigated. However, there is little knowledge about suitable fluorescent molecules for rKACB, and the application of rKACB has been limited to the analysis of hairpins and duplex structures of nucleic acids. In this work, various fluorescent molecules, including Alexa 488, R6G, TAMRA, ATTO 647N and ATTO 655, were evaluated for rKACB. Moreover, rKACB was adapted to the discrimination of DNA/DNA and DNA/RNA nucleic acid duplexes and investigation of antigen–antibody interactions. By changing the size of the oxidant, it was possible to determine the solvent accessibility of the target domain of the analyzed biomolecules.Analysis in a blink: Kinetic analysis based on the control of fluorescence blinking utilizing redox reactions (rKACB) was investigated for various fluorescent molecules and for different oxidant sizes (see figure). rKACB was shown to be adaptable to the discrimination of B-form DNA/DNA and A-like DNA/RNA helixes, as well as to single-molecule measurements of antigen–antibody interactions.
      PubDate: 2018-03-07T10:32:51.082597-05:
      DOI: 10.1002/chem.201705668
  • UDP-GlcNAc Analogs as Inhibitors of O-GlcNAc Transferase (OGT):
           Spectroscopic, Computational and Biological Studies
    • Authors: Pedro Merino; Mattia Ghirardello, Daniela Perrone, Nicola Chinaglia, David Sadaba, Ignacio Delso, Tomas Tejero, Elena Marchesi, Marco Fogagnolo, Karim Rafie, Daan M. F. van Aalten
      Abstract: A series of glycomimetics of UDP-GlcNAc in which the β-phosphate has been replaced by either an alkyl chain or a triazolyl ring and the sugar moiety has been replaced by a pyrrolidine ring have been synthesized by using different click-chemistry procedures. Their affinity for human O-GlcNAc transferase (hOGT) has been evaluated and both spectroscopically and computationally studied. The binding epitopes of the best ligands have been determined in solution using saturation transfer difference (STD) NMR spectroscopy. Experimental, spectroscopic and computational results are in agreement, pointing out the essential role for binding of the β-phosphate. We have found that the loss of interactions from the -phosphate can be counterbalanced by the presence of hydrophobic groups at a pyrroline ring acting as a surrogate of the carbohydrate unit. Two of the glycomimetics prepared reach inhibition in the micromolar scale.
      PubDate: 2018-03-07T08:45:27.645973-05:
      DOI: 10.1002/chem.201801083
  • Enantioselective Alkylation of 2-Oxindoles Catalyzed by a Bifunctional
           Phase-Transfer Catalyst: Synthesis of (−)-Debromoflustramine B
    • Authors: Ryan Craig; Emiliano Sorrentino, Stephen J. Connon
      Abstract: A new bifunctional phase-transfer catalyst that employs hydrogen bonding as a control element was developed to promote efficient enantioselective SN2 reactions for the construction all-carbon quaternary stereocenters in high yield and excellent enantioselectivity (up to 97 % ee) utilizing the alkylation of a malleable oxindole substrate. The utility of the methodology was demonstrated through a concise and highly enantioselective synthesis of (−)-debromoflustramine B.A highly enantioselective alkylation of 3-substituted oxindoles with a broad range of electrophiles was developed using a novel, bulky bifunctional phase transfer catalyst. The methodology was applied to the catalytic asymmetric total synthesis of (−)-debromoflustramine B.
      PubDate: 2018-03-07T08:41:26.111344-05:
      DOI: 10.1002/chem.201800313
  • Cyclodextrin-Sandwiched Hexaphyrin Hybrids: Side-to-Side Cavity Coupling
           Switched by a Temperature- and Redox-Responsive Central Device
    • Authors: Mickaël Ménand; Matthieu Sollogoub, Bernard Boitrel, Stéphane Le Gac
      Abstract: Targeting adaptive receptors for allosteric enzyme mimicry, sandwich hybrids composed of a hexaphyrin capped by two cyclodextrins have been synthesized. The hexaphyrin behaves as a dual-responsive device which couples the two cyclodextrins in a switchable manner through redox ([anti]aromaticity) and thermal (conformation) control. Conformational isomerization of the central unit tunes the access to the twin confined spaces being either locked or unlocked for both aromatic and antiaromatic states. This four-state system controlled by two orthogonal switches offers an interesting playground for further allosteric regulation. More information can be found in the Full Paper by M. Ménand, S. Le Gac et al. (
      DOI : 10.1002/chem.201705958).
      PubDate: 2018-03-07T08:40:33.683306-05:
  • Electrochemical C-O Bond Formation: A Facile Access to Aromatic Lactones
    • Authors: Jian-Jun Dai; Xiang-Zhang Tao, Jie Zhou, Jun Xu, Hua-Jian Xu
      Abstract: An efficient and robust methodology based on electrochemical techniques for the direct synthesis of aromatic lactones via dehydrogenative C-O cyclization is described. This new and useful electrochemical reaction can tolerate a variety of functional groups, and is scalable to 100 grams under mild conditions. Remarkably, heterocycle-containing substrates can be employed, thus expanding the scope of radical C-O cyclization reaction.
      PubDate: 2018-03-07T07:46:24.72437-05:0
      DOI: 10.1002/chem.201801108
  • The Dynamics of Chemical Reactions: Atomistic Visualizations of Organic
           Reactions, and Homage to van ’t Hoff
    • Authors: Zhongyue Yang; K. N. Houk
      Abstract: Jacobus Henricus van ’t Hoff (1852, Rotterdam–1911, Berlin) received the Nobel Prize for Chemistry in 1901 “in recognition of the extraordinary services he has rendered by the discovery of the laws of chemical dynamics and osmotic pressure in solutions”. van ’t Hoff was born the Netherlands, and earned his doctorate in Utrecht in 1874. In 1896 he moved to Berlin, where he was offered a position with more research and less teaching. van ’t Hoff is considered one of the founders of physical chemistry. A key step in establishing this new field was the start of Zeitschrift für Physikalische Chemie in 1887.Jacobus Henricus van ’t Hoff was the first Nobel Laureate in Chemistry. He pioneered in the study of chemical dynamics, which referred at that time to chemical kinetics and thermodynamics. The term has evolved in modern times to refer to the exploration of chemical transformations in a time-resolved fashion. Chemical dynamics has been driven by the development of molecular dynamics trajectory simulations, which provide atomic visualization of chemical processes and illuminate how dynamic effects influence chemical reactivity and selectivity. In homage to the legend of van ’t Hoff, we review the development of the chemical dynamics of organic reactions, our area of research. We then discuss our trajectory simulations of pericyclic reactions, and our development of dynamic criteria for concerted and stepwise reaction mechanisms. We also describe a method that we call environment-perturbed transition state sampling, which enables trajectory simulations in condensed-media using quantum mechanics and molecular mechanics (QM/MM). We apply the method to reactions in solvent and in enzyme.On the shoulders of giants: The first Nobel Prize in Chemistry was awarded to van't Hoff in 1901 for the discovery of the laws of chemical dynamics. Since then, the study of chemical dynamics has been advanced by the development of molecular dynamics simulations and QM/MM calculations. In the first of a series entitled The Nobel Legacy, van't Hoff's achievements and their influence on modern chemistry are reviewed.
      PubDate: 2018-03-07T07:41:09.442937-05:
      DOI: 10.1002/chem.201706032
  • Improvement of Photodynamic Activity of Lipid-Membrane-Incorporated
           Fullerene Derivative by Combination with a Photo-Antenna Molecule
    • Authors: Daiki Antoku; Shuhei Satake, Tomoya Mae, Kouta Sugikawa, Hisakage Funabashi, Akio Kuroda, Atsushi Ikeda
      Abstract: The weak absorbance of pristine C₆₀, C₇₀, and fullerene derivatives at wavelengths over 600 nm hampers the use of these molecules as photosensitizers (PSs) for photodynamic therapy (PDT). The coexistence of light-harvesting antenna molecules with a fullerene derivative in lipid membrane bilayers solved this issue. By controlling the location of the C₆₀ derivative in the lipid membrane, the liposomal dyad system for PDT improved the photodynamic activity via an efficient photoenergy transfer from antenna molecules to the fullerene derivative. The photodynamic activity was found to be much higher than those of dyad systems using pristine C₆₀ and C₇₀.
      PubDate: 2018-03-07T06:15:30.961803-05:
      DOI: 10.1002/chem.201800674
  • Sulfur Hydrogen Bonding in Isolated Monohydrates: Furfuryl Mercaptan
           versus Furfuryl Alcohol
    • Authors: Marcos Juanes; Alberto Lesarri, Ruth Pinacho, Elena Charro, José E. Rubio, Lourdes Enríquez, Martín Jaraíz
      Abstract: The hydrogen bonds involving sulfur in the furfuryl mercaptan monohydrate are compared with the interactions originating from the hydroxyl group in furfuryl alcohol. The dimers with water were created in a supersonic jet expansion and characterized using microwave spectroscopy and supporting molecular orbital calculations. In furfuryl alcohol–water, a single isomer is observed, in which the water molecule forms an insertion complex with two simultaneous hydrogen bonds to the alcohol (O−H⋅⋅⋅Ow) and the ring oxygen (Ow−H⋅⋅⋅Or). When the alcohol is replaced by a thiol group in furfuryl mercaptan–water, two isomers are observed, with the thiol group preferentially behaving as proton donor to water. The first isomer is topologically equivalent to the alcohol analog but the stronger hydrogen bond is now established by water and the ring oxygen, assisted by a thiol S−H⋅⋅⋅Ow hydrogen bond. In the second isomer the sulfur group accepts a proton from water, forming a Ow−H⋅⋅⋅S hydrogen bond. Binding energies for the mercaptan–water dimer are predicted around 12 kJ mol−1 weaker than in the alcohol hydrate (B3LYP-D3(BJ)). The non-covalent interactions in the furfuryl dimers are dominantly electrostatic according to a SAPT(0) energy decomposition, but with increasing dispersion components in the mercaptan dimers, which are larger for the isomer with the weaker Ow−H⋅⋅⋅S interaction.Sulfur hydrogen bonds: Monohydrates generated in a jet expansion illustrate the hydrogen bonding differences between thiols and alcohols.
      PubDate: 2018-03-07T06:06:24.639875-05:
      DOI: 10.1002/chem.201705727
  • Copper-Catalyzed Regio- and Enantioselective Aminoboration of Unactivated
           Terminal Alkenes
    • Authors: Kodai Kato; Koji Hirano, Masahiro Miura
      Abstract: A CuCl/(R,R)-PTBP-BDPP-catalyzed regioselective and enantioselective aminoboration of simple and unactivated terminal alkenes with bis(pinacolato)diboron (pinB-Bpin) and hydroxylamines has been developed. The amino group and boryl group are incorporated at the internal position and terminal position, respectively, and the corresponding chiral beta-borylalkylamines are obtained with good to high enantiomeric ratios. The asymmetric copper catalysis allows for rapid and concise transformation of readily available olefinic feedstock-like materials into functionalized chiral alkylamines of high potential in medicinal and pharmaceutical chemistry.
      PubDate: 2018-03-07T04:42:58.955109-05:
      DOI: 10.1002/chem.201801070
  • Novel Highly Sensitive Fluorogenic Probe for Imaging Glycoproteins and
           Mucine Activity in Live Cells in the Near Infrared Region
    • Authors: Cecilia Samaniego Lopez; Jimena Hebe Martínez, María Laura Uhrig, Federico Coluccio Leskow, Carla Cecilia Spagnuolo
      Abstract: We introduce a novel fluorescent molecular probe able to detect glycoproteins, especially mucins, with high sensitivity and with a turn-on response along with a large Stokes shift (>130 nm), within the biologically active window. The probe contains an aminotricarbocyanine as the fluorescent reporter with a linked benzoboroxole as the recognition unit, which operates through a dynamic covalent reaction between the boronic hemiester residue of the receptor and cis-diols of the analyte. The superior selectivity of the probe is displayed by the labeling of mucins present in Calu-3 cells. The new benzoboroxole fluorescent derivative gathers together key properties to meet high rated molecular probes: specificity, excellent solubility in water and off-on near infrared emission. The probe we provide is expected to be an excellent tool for imaging intracellular mucin to evaluate mucus related diseases as well as a sensing strategy towards glycosylated structures with a high potential for theranostics approaches in biological samples.
      PubDate: 2018-03-07T04:37:21.960922-05:
      DOI: 10.1002/chem.201800790
  • Simultaneous G-Quadruplex DNA Logic
    • Authors: Antoine Bader; Scott L. Cockroft
      Abstract: A fundamental principle of digital computer operation is Boolean logic, where inputs and outputs are described by binary integer voltages. Similarly, inputs and outputs may be processed on the molecular level as exemplified by synthetic circuits that exploit the programmability of DNA base-pairing. Unlike modern computers, which execute large numbers of logic gates in parallel, most implementations of molecular logic have been limited to single computing tasks, or sensing applications. This work reports three G-quadruplex-based logic gates that operate simultaneously in a single reaction vessel. The gates respond to unique Boolean DNA inputs by undergoing topological conversion from duplex to G-quadruplex states that were resolved using a thioflavin T dye and gel electrophoresis. The modular, addressable, and label-free approach could be incorporated into DNA-based sensors, or used for resolving and debugging parallel processes in DNA computing applications.All in one: Three DNA-based Boolean logic gates are simultaneously computed in a single reaction vessel. G-quadruplex outputs were specifically detected against a complicated background of oligonucleotide species giving a quantized four-state (0, 1, 2, 3) output, which contrasts with the binary (0, 1) nature of Boolean logic.
      PubDate: 2018-03-07T03:46:09.572862-05:
      DOI: 10.1002/chem.201800756
  • 2,2′-Bipyridine Equipped with a Disulfide/Dithiol Switch for Coupled
           Two-Electron and Two-Proton Transfer
    • Authors: Mauricio Cattaneo; Christine E. Schiewer, Anne Schober, Sebastian Dechert, Inke Siewert, Franc Meyer
      Abstract: [1,2]Dithiino[4,3-b:5,6-b′]dipyridine (1) and its protonated open form 3,3′-dithiol-2,2′-bipyridine (2) were synthesised and their interconversion investigated. The X-ray structure of 2 revealed an anti orientation of the two pyridine units and a zwitterionic form. In depth electrochemical studies in combination with DFT calculations lead to a comprehensive picture of the redox chemistry of 1 in the absence and presence of protons. Initial one-electron reduction at E1=−1.20 V results in the formation of the radical anion 1red with much elongated S−S bond, which readily undergoes further reduction at E2=−1.38 V. Water triggers a potential inversion (E≥−1.13 V for the second reduction) as the radical anion 1red is protonated at its basic N atom. DFT studies revealed that S−S bond breaking and twisting of the pyridine units generally occurs after the second reduction step, whereas the potential inversion induced by protonation is a result of charge compensation. The CV data were simulated to derive rate constants for the individual chemical and electrochemical reactions for both scenarios in the absence and presence of protons.Couples and switches: Electrochemical investigation of a new dithiine that amalgamates the 2 e−/2 H+ disulfide/dithiol couple with the 2,2′-bipyridine scaffold shows that protonation by a weak acid such as water facilitates the second reduction and triggers potential inversion while inducing a switch from an EEC mechanism to an ECEC mechanism.
      PubDate: 2018-03-06T07:51:25.819036-05:
      DOI: 10.1002/chem.201705022
  • Single Ion Magnets from 3d to 5f: Developments and Strategies
    • Authors: Min Feng; Ming-Liang Tong
      Abstract: Single-ion magnets (SIMs), exhibiting slow magnetization relaxation in the absence of the magnetic field, originate from their single spin-carrier centre. In pursuit of high-performance magnetic properties, such as high spin-reversal barrier and high blocking temperature, various metal centres were investigated to establish SIMs, including 3d and 5d transition metal ions, 4f lanthanide ions, and 5f actinide ions, which possess unique zero-field splitting and magnetic properties. Therefore, proper ligand field is of great importance to different types of metals. In the given great breakthroughs since the first SIM, [Pc2Tb]− (Pc=dianion of phthalocyanine), was reported, strategies of ligand field design have emerged. In this review, the developments of SIMs with different metal centres are summarized, as well as the possible strategies.How molecular magnetism works: A summary of single-ion magnets (SIMs) including the development of 3d, 5d, 4f, and 5f metal-based SIMs and the possible ligand field strategies for high-performance SIMs constructions.
      PubDate: 2018-03-06T07:47:32.570242-05:
      DOI: 10.1002/chem.201705761
  • Prebiotic Chemistry of HCN Tetramerization by Automated Reaction Search
    • Authors: Surajit Nandi; Debankur Bhattacharyya, Anakuthil Anoop
      Abstract: HCN oligomerization is considered to be one of the important pathways in chemical evolution. Nucleobases, aminoacids, and many other complex organic molecules can evolve through this pathway. We report an explorative study based on an automated reaction search method that avoids the cognitive bias present when searching chemical reaction space. We discuss the chemical space of the HCN dimer in detail, and the important trimers and tetramers are discussed briefly. A component-wise molecular-fingerprint-based methodology is proposed to identify molecular similarity. We present four different thermal routes to cis/trans-2,3-diaminomaleonitrile and 4-amino-1H-imidazole-5-carbonitrile, which are important intermediates in prebiotic chemistry.An exploration through prebiotic chemistry: The oligomerization of HCN en route to the precursor molecules of nucleobases was explored by using an automated reaction search method. We found energetically favorable, unexplored pathways by this automated exploration.
      PubDate: 2018-03-06T07:47:20.962207-05:
      DOI: 10.1002/chem.201705492
  • Achieving Skeletal Diversity in Peptide Macrocycles through The Use of
           Heterocyclic Grafts
    • Authors: Sherif J. Kaldas; Andrei K. Yudin
      Abstract: Despite their therapeutic potential, peptide macrocycles often suffer from drawbacks such as low membrane permeability, proteolytic instability, and conformational lability. As a result, there have been significant efforts to “depeptidize” amino acid-rich macrocycles through the incorporation of heterocyclic grafts into their backbones. In this concept article, we summarize selected recent methodologies that can be used to introduce heterocycles into cyclic peptides.More structurally diverse, conformationally homogeneous, membrane permeable, and stable macrocycles can be obtained by grafting heterocycles into the macrocycle backbone. This should improve the low membrane permeability, proteolytic instability and conformational heterogeneity which is usually observed.
      PubDate: 2018-03-06T07:47:11.312137-05:
      DOI: 10.1002/chem.201705418
  • Coupling Influences SMM Properties for Pure 4 f Systems
    • Authors: Xuejing Zhang; Shuang Liu, Veacheslav Vieru, Na Xu, Chen Gao, Bing-Wu Wang, Wei Shi, Liviu F. Chibotaru, Song Gao, Peng Cheng, Annie K. Powell
      Abstract: Increasing both the energy barrier for magnetization reversal and the coercive field of the hysteresis loop are significant challenges in the field of single-molecule magnets (SMMs). Coordination geometries of lanthanide ions and magnetic interactions between lanthanide ions are both important for guiding the magnetic behavior of SMMs. We report a high energy barrier of 657 K (457 cm−1) in a diamagnetic-ion-diluted lanthanide chain compound with a constrained bisphenoid symmetry (D2d); this energy barrier is substantially higher than the barrier of 567 K (394 cm−1) of the non-diluted chain compound with intrachain ferromagnetic interactions. Although intrachain magnetic interaction lowers the energy barrier for magnetization reversal, it can greatly enhance the coercive fields and zero-field remanence of the hysteresis loops, which is crucial for the rational design of high-performance SMMs. Factors related to the coordination sphere of the lanthanide center, which govern the high magnetic relaxation barriers through the second excited Kramer's doublets and the magnetic interactions that affect the hysteresis loops, were revealed through ab initio calculations.Nice chains: A new coordination chain compound (see figure) is introduced as a single-molecule magnet (SMM) assembly for fine tuning both the magnetization dynamics and the hysteresis loops of DyIII SMMs that serve as inorganic node. Although intrachain magnetic interaction lowers the energy barrier for magnetization reversal, it can greatly enhance the coercive fields and zero-field remanence of the hysteresis loops.
      PubDate: 2018-03-06T07:46:48.011514-05:
      DOI: 10.1002/chem.201705350
  • Anion Sensing by Fluorescent Expanded Calixpyrroles
    • Authors: Mariia Pushina; Petr Koutnik, Ryuhei Nishiyabu, Tsuyoshi Minami, Pavel Savechenkov, Pavel Anzenbacher
      Abstract: Expanded calixpyrrole-type macrocycles, calix[2]benzo[4]pyrroles, bearing fluorescent moieties attached via conjugated vinyl spacers, have been synthesized from the corresponding formyl derivatives through Knoevenagel condensation. The anion-binding properties of the resulting fluorescent macrocycles have been studied by means of NMR, UV/Vis, and fluorescence spectroscopies. Our main focus has been on dicarboxylates matching the size of the binding cavity of the calix[2]benzo[4]pyrrole skeleton. The observed anion-binding properties were compared with those of the regular calix[4]pyrroles bearing identical fluorophores. Surprisingly, the parent calix[4]pyrroles appear to be equally efficient, if not more so, for sensing anions such as dicarboxylates. Affinity constants determined for various anions and dianions show the sensors S1–S5 to be highly cross-reactive. The cross-reactivity of the sensors was utilized in a microchip-based array, which showed perfect (100 %) classification of 18 analytes utilizing only five sensors. Finally, the same array was used to quantitatively analyze dicarboxylates such as oxalate and malonate. The data from the array were subjected to linear regression, allowing the determination of various concentrations of dianions with low error (
      PubDate: 2018-03-06T07:46:35.405138-05:
      DOI: 10.1002/chem.201705387
  • A biomimetic synthetic receptor selectively recognizing fucose in water.
    • Authors: Oscar Francesconi; Marco Martinucci, Lorenzo Badii, Cristina Nativi, Stefano Roelens
      Abstract: Carbohydrate recognition in water by biomimetic receptors is an attractive but very challenging goal. Despite the advances achieved on glucose recognition, little or no success has been obtained in the recognition of other saccharidic epitopes of paramount importance in biological processes. Here we report the unprecedented recognition of fucose in water by an artificial receptor that shows affinities closely comparable to those of several lectins. The receptor has been build-up by assembling a hydrogen bonding element (carbazole), a hydrophobic aromatic moiety (anthracene), and a water-solubilizing function (phosphonate) into a macrocyclic structure providing the appropriate binding geometry. The described receptor binds fucose with sub-millimolar affinity in water at physiological pH, showing enthalpic binding that can be ascribed to H-bonding to saccharidic hydroxyls and to CH-π interactions between the sugar backbone and the aromatic moieties. Experimental NOE contacts coupled to conformational search calculations return a picture of a binding site in which fucose assumes a staggered orientation reminiscent of that shown by fucose when bound to the bacterial lectin RSL.
      PubDate: 2018-03-06T07:01:40.479028-05:
      DOI: 10.1002/chem.201800390
  • Ordered mesoporous titania/carbon hybrid monoliths for lithium-ion battery
           anodes with high areal and volumetric capacity
    • Authors: Tobias S Dörr; Simon Fleischmann, Marco Zeiger, Ingrid Grobelsek, Peter W de Oliveira, Volker Presser
      Abstract: Free-standing, binder-free, and conductive additive-free mesoporous titanium dioxide/carbon hybrid electrodes were prepared from co-assembly of a poly(isoprene)-block-poly(styrene)-block-poly(ethylene oxide) block copolymer and a titanium alkoxide. By tailoring an optimized morphology, we prepared macroscopic mechanically stable 300 µm thick monoliths that were directly employed as lithium-ion battery electrodes. High areal mass loading of up to 26.4 mg/cm2 and a high bulk density of 0.88 g/cm3 were obtained. This resulted in a highly increased volumetric capacity of 155 mAh/cm3, compared to casted thin film electrodes. Further, the areal capacity of 4.5 mAh/cm2 represented a 9-fold increase compared to conventionally casted electrodes. These attractive performance metrics are related to the superior electrolyte transport and shortened diffusion lengths provided by the interconnected mesoporous nature of the monolith material, assuring superior rate handling even at high cycling rates.
      PubDate: 2018-03-06T05:55:32.924964-05:
      DOI: 10.1002/chem.201801099
  • Formation and Properties of Poly(Ionic Liquid)-Carbene Nanogels Containing
           Individually Stabilized Silver Species
    • Authors: Han Miao; Johannes Schmidt, Tobias Heil, Markus Antonietti, Marc Willinger, Ryan Guterman
      Abstract: Imidazolium-based ionic liquids have the ability to undergo a variety of chemical reactions through an N-heterocyclic carbene (NHC) intermediate, which has expanded the chemical toolbox for new applications. Despite their uses and exploration, the carbene-forming properties and applications of their polymeric congeners, poly(ionic liquid)s (PILs), is still underdeveloped. In this work we explore the NHC-forming properties of a theophylline-derived PIL for nanogel synthesis. Using silver oxide as both the carbene forming reagent and crosslinker, nanogels containing individually stabilized ions can be created with different sizes and morphology, including large "galaxy-like" superstructures. Using high-resolution TEM techniques, we directly observed the sub-nanometer structure of these constructs. This features combined exemplifies the unique chemistry of poly-NHCs for single metal ion stabilization nanogel design.
      PubDate: 2018-03-06T05:25:40.038789-05:
      DOI: 10.1002/chem.201800448
  • Stable Nitrogen-Centered Bis(imino)rylene Diradicaloids
    • Authors: Wangdong Zeng; Yongseok Hong, Samara Medina Rivero, Jinseok Kim, José L. Zafra, Hoa Phan, Tullimilli Y. Gopalakrishna, Tun Seng Herng, Jun Ding, Juan Casado, Dongho Kim, Jishan Wu
      Abstract: The synthesis of stable open-shell singlet diradicaloids is critical for their practical material application. So far, most reported examples are based on carbon-centered radicals, which are intrinsically reactive, and there are very few examples of stable nitrogen-centered diradicaloids. In this full paper, a series of soluble and stable bis(imino)rylenes up to octarylene were synthesized on the basis of newly developed dibromorylene intermediates. It was found that from hexarylene onward, these quinoidal rylenes showed open-shell singlet ground states and could be thermally populated to paramagnetic triplet aminyl diradicals. They are stable due to efficient spin delocalization onto the rylene backbone as well as kinetic blocking of the aminyl sites by the bulky and electron-deficient 2,4,6-trichlorophenyl groups. They exhibited very different electronic structures, diradical character, excited-state dynamics, one-photon absorption, two-photon absorption, and electrochemical properties from their respective aromatic rylene counterparts. These bis(imino)rylenes represent a rare class of stable, neutral, nitrogen-centered aminyl diradicaloids.Long rylene-bridged aminyl diradicaloids! We report the successful synthesis of a series of bis(imino)rylenes up to octarylene. The long quinoidal rylenes from hexarylene onward show an open-shell singlet ground state. Their electronic structures and physical properties are very different from those of their aromatic rylene counterparts.
      PubDate: 2018-03-06T04:37:52.160364-05:
      DOI: 10.1002/chem.201706041
  • Crystal Nucleation of Tolbutamide in Solution: Relationship to Solvent,
           Solute Conformation, and Solution Structure
    • Authors: Jacek Zeglinski; Manuel Kuhs, Dikshitkumar Khamar, Avril C. Hegarty, Renuka K. Devi, Åke C. Rasmuson
      Abstract: The influence of the solvent in nucleation of tolbutamide, a medium-sized, flexible and polymorphic organic molecule, has been explored by measuring nucleation induction times, estimating solvent–solute interaction enthalpies using molecular modelling and calorimetric data, probing interactions and clustering with spectroscopy, and modelling solvent-dependence of molecular conformation in solution. The nucleation driving force required to reach the same induction time is strongly solvent-dependent, increasing in the order: acetonitrile
      PubDate: 2018-03-06T04:36:52.742157-05:
      DOI: 10.1002/chem.201705954
  • Expanding the Breadth of 4-Amino-1,8-naphthalimide Photophysical
           Properties through Substitution of the Naphthalimide Core
    • Authors: Kathryn G. Leslie; Denis Jacquemin, Elizabeth J. New, Katrina A. Jolliffe
      Abstract: Fluorescent sensors that illuminate specific molecules and chemical events allow the selective and sensitive study of the cellular environment. At the centre of this technology lies the fluorescent reporter molecule, and it is therefore crucial to provide a breadth of fluorophores with varying photophysical and biological behaviour. 4-Amino-1,8-naphthalimides are commonly employed in fluorescent sensors, but the narrow range of structural derivatives limits versatility of application. Here we report the synthesis and investigation of a set of twelve 4-amino-1,8-naphthalimides bearing an additional substituent on the aromatic core. Photophysical characterisation and time-dependent density functional theory studies provided insights into the structure–photophysical property relationships of these derivatives, which show an expanded range of emission wavelengths and other photophysical properties. These compounds could all be visualised within cells by confocal microscopy, showing cytoplasmic or lipid droplet localisation. Our studies have demonstrated that simple structural modification of 4-amino-1,8-naphthalimides provides derivatives with considerable breadth of behaviour that lend valuable versatility to the design of fluorescent sensors.Changing behaviour: Substitution of the 4-amino- 1,8-naphthalimide core tunes both the photophysical properties and biological behaviour of this versatile fluorophore.
      PubDate: 2018-03-06T04:36:17.572421-05:
      DOI: 10.1002/chem.201705546
  • Electron-Catalyzed Coupling of Magnesium Amides with Aryl Iodides
    • Authors: Kazuya Kiriyama; Keisho Okura, Fumiko Tamakuni, Eiji Shirakawa
      Abstract: An electron was found to catalyze the coupling of magnesium diarylamides with aryl iodides giving triarylamines through a radical-anion intermediate. The transformation requires no transition metal catalysts or additives, and a wide array of products are formed in good-to-excellent yields.A single electron floating in a solvent, serving arylamines: An electron was found to catalyze the coupling of magnesium diarylamides with aryl iodides giving triarylamines. The transformation requires no transition metal catalysts or additives.
      PubDate: 2018-03-06T04:32:00.155734-05:
      DOI: 10.1002/chem.201800011
  • Front Cover: Brønsted Acid-Catalyzed Tandem Cyclizations of
           Tryptamine-Ynamides Yielding 1H-Pyrrolo[2,3-d]carbazole Derivatives (Chem.
           Eur. J. 16/2018)
    • Authors: Yanshi Wang; Jingsheng Lin, Xiaoyu Wang, Guanghui Wang, Xinhang Zhang, Bo Yao, Yuandong Zhao, Pengfei Yu, Bin Lin, Yongxiang Liu, Maosheng Cheng
      Pages: 3909 - 3909
      Abstract: A highly efficient novel method for the construction of the core tetracyclic motif of numerous biologically active indole alkaloids was described. The cyclization precursors were easily prepared from tryptamine derivatives in five steps with excellent yields. The full potential of the developed method was demonstrated by the synthesis of Büchi ketone, a well-known intermediate in the synthesis of vindorosine. More information can be found in the Full Paper by Y. Liu, M. Cheng et al. on page 4026.
      PubDate: 2018-01-17T08:10:59.505172-05:
      DOI: 10.1002/chem.201706014
  • Cover Feature: Safe-by-Design Ligand-Coated ZnO Nanocrystals Engineered by
           an Organometallic Approach: Unique Physicochemical Properties and Low
           Toxicity toward Lung Cells (Chem. Eur. J. 16/2018)
    • Authors: Małgorzata Wolska-Pietkiewicz; Katarzyna Tokarska, Agnieszka Grala, Anna Wojewódzka, Elżbieta Chwojnowska, Justyna Grzonka, Piotr J. Cywiński, Krzysztof Kruczała, Zbigniew Sojka, Michał Chudy, Janusz Lewiński
      Pages: 3910 - 3910
      Abstract: One-pot self-supporting organometallic (OSSOM) method was successfully extended towards an efficient “safe-by-design” strategy for the preparation of bio-friendly quantum-sized ZnO crystals coated by densely packed ligand shell. The observed unique physicochemical properties, such as ultra-long photoluminescence decay, EPR silence under standard condition, inertness in biological environment, and negligible negative impact on the selected mammalian cell lines, clearly demonstrated that the OSSOM approach gives ZnO nanocrystals with exceptional nanocrystal–ligand interface and facilitates their use in biology. More information can be found in the Full Paper by J. Lewiński et al. on page 4033.
      PubDate: 2018-01-29T08:32:47.653738-05:
      DOI: 10.1002/chem.201706012
  • Cover Feature: Isomerization of Allylic Alcohols to Ketones Catalyzed by
           Well-Defined Iron PNP Pincer Catalysts (Chem. Eur. J. 16/2018)
    • Authors: Tian Xia; Zhihong Wei, Brian Spiegelberg, Haijun Jiao, Sandra Hinze, Johannes G. de Vries
      Pages: 3911 - 3911
      Abstract: A well-defined iron pincer complex has been successfully applied for the isomerization of allylic and homo-allylic alcohols to the corresponding ketones. A range of differently substituted aromatic as well as aliphatic allylic alcohols are suitable candidates. The addition of KOtBu leads to the formation of the active catalyst, which performs the isomerization by a two-step self-hydrogen-borrowing process. The mechanism was verified using DFT calculations. More information can be found in the Full Paper by J. G. de Vries, et al. on page 4043.
      PubDate: 2018-01-29T08:41:16.395445-05:
      DOI: 10.1002/chem.201800129
  • Cover Feature: Self-Assembly Process of a Pd2L4 Capsule: Steric
           Interactions between Neighboring Components Favor the Formation of Large
           Intermediates (Chem. Eur. J. 16/2018)
    • Authors: Shumpei Kai; Masanori Nakagawa, Tatsuo Kojima, Xin Li, Masahiro Yamashina, Michito Yoshizawa, Shuichi Hiraoka
      Pages: 3912 - 3912
      Abstract: The self-assembly of a Pd2L4 capsule consisting of Pd(II) ions and ditopic ligands comprising an anthracene panel takes place mainly through three pathways, as determined by QASAP (quantitative analysis of self-assembly process). This differs substantially from the self-assembly process of a geometrically similar Pd2L4 cage without anthracene panels, indicating that the interactions between the neighboring panels have a significant influence on the self-assembly process. More information can be found in the Communication by S. Hiraoka et al. on page 3965.
      PubDate: 2018-02-06T09:09:06.691035-05:
      DOI: 10.1002/chem.201800146
  • Brønsted Acid-Catalyzed Tandem Cyclizations of Tryptamine-Ynamides
           Yielding 1H-Pyrrolo[2,3-d]carbazole Derivatives
    • Authors: Yanshi Wang; Jingsheng Lin, Xiaoyu Wang, Guanghui Wang, Xinhang Zhang, Bo Yao, Yuandong Zhao, Pengfei Yu, Bin Lin, Yongxiang Liu, Maosheng Cheng
      Pages: 3913 - 3913
      Abstract: Invited for the cover of this issue are the groups of Yongxiang Liu and Maosheng Cheng at Shenyang Pharmaceutical University. The image depicts a tetracyclic indoline, a core scaffold in a series of indole alkaloids. Read the full text of the article at 10.1002/chem.201705189.“…the inherent tendency of C−C bond migration through Wagner–Meerwein rearrangement to generate a tricyclic fused ring system was circumvented by an instantaneous intramolecular nucleophilic trap to indoleninium.” Read more about the story behind the cover in the Cover Profile and about the research itself on page 4026 ff. (
      DOI : 10.1002/chem.201705189).
      PubDate: 2018-01-16T03:51:13.213905-05:
  • The Nobel Legacy: A Journey through Chemistry Inspired by the Achievements
           of Nobel Laureates
    • Authors: Francesca Rita Novara; Haymo Ross
      Pages: 3914 - 3915
      Abstract: The Prize is right! Chemistry—A European Journal will start an exciting journey exploring the significance of Nobel Prize awards in Chemistry in the corresponding contemporary chemistry fields. In this new journal feature called “The Nobel Legacy”, a recurring series of invited Review-type articles each one connected to a particular Nobel Prize in Chemistry will be published.
      PubDate: 2018-03-06T04:31:50.174861-05:
      DOI: 10.1002/chem.201800664
  • Organic-Inorganic Hybrid Materials: Multi-Functional Solids for Multi-Step
           Reaction Processes
    • Authors: Urbano Díaz; Avelino Corma
      Pages: 3944 - 3958
      Abstract: The design of new hybrid materials with tailored properties at the nano-, meso-, and macro-scale, with the use of structural functional nanobuilding units, is carried out to obtain specific multi-functional materials. Organization into controlled 1D, 2D, and 3D architectures with selected functionalities is key for developing advanced catalysts, but this is hardly accomplished using conventional synthesis procedures. The use of pre-formed nanostructures, derived either from known materials or made with specific innovative synthetic methodologies, has enormous potential in the generation of multi-site catalytic materials for one-pot processes. The present concept article introduces a new archetype wherein self-assembled nanostructured builder units are the base for the design of multifunctional catalysts, which combine catalytic efficiency with fast reactant and product diffusion. The article addresses a new generation of versatile hybrid organic-inorganic multi-site catalytic materials for their use in the production of (chiral) high-added-value products within the scope of chemicals and fine chemicals production. The use of those multi-reactive solids for more nanotechnological applications, such as sensors, due to the inclusion of electron donor-acceptor structural arrays is also considered, together with the adsorption-desorption capacities due to the combination of hydrophobic and hydrophilic sub-domains. The innovative structured hybrid materials for multipurpose processes here considered, can allow the development of multi-stage one-pot reactions with industrial applications, using the materials as one nanoreactor systems, favoring more sustainable production pathways with economic, environmental and energetic advantages.The use of pre-formed nanobuilding units with associated functionalities are necessary to prepare hybrid multi-functional materials to perform multipurpose processes in the fields of catalysis, sensing and for materials science.
      PubDate: 2018-01-25T09:18:22.737961-05:
      DOI: 10.1002/chem.201704185
  • Bioconjugation with Thiols by Benzylic Substitution
    • Authors: Kenji Watanabe; Takashi Ohshima
      Pages: 3959 - 3964
      Abstract: A benzylic substitution of 3-indolyl(hydroxyl)acetate derivatives with thiols proceeded specifically in the presence of amino, carboxy, and phosphate groups in weakly acidic aqueous solutions under nearly physiological condition, while no reaction occurred at pH over 7. Kinetic studies revealed that the reaction followed second-order kinetics (first-order in the reactant and first-order in thiol) in contrast with the SN1 mechanism of common benzylic substitution of alcohols. The utility of the present method for functionalization of biomacromolecules was demonstrated using several model proteins, such as lysozyme, insulin, trypsin, and serum albumin. The catalytic bioactivity of lysozyme in lysis of Micrococcus lysodeikticus cells was completely retained after the modification.A benzylic substitution of 3-indolyl(hydroxyl)acetate derivatives with thiols proceeded specifically in the presence of amino, carboxy, and phosphate groups in weakly acidic aqueous solutions under physiological conditions. The utility of the present method for functionalization of proteins was demonstrated.
      PubDate: 2018-02-19T02:46:50.107548-05:
      DOI: 10.1002/chem.201706149
  • Self-Assembly Process of a Pd2L4 Capsule: Steric Interactions between
           Neighboring Components Favor the Formation of Large Intermediates
    • Authors: Shumpei Kai; Masanori Nakagawa, Tatsuo Kojima, Xin Li, Masahiro Yamashina, Michito Yoshizawa, Shuichi Hiraoka
      Pages: 3965 - 3969
      Abstract: The effect of molecular interactions between the components on the self-assembly process of Pd2L4 structures was investigated by a 1H NMR-based quantitative approach (QASAP: quantitative analysis of self-assembly process). Although the self-assembly of the Pd2L4 cage without interactions between the bent ligands took place, mainly producing small intermediates, the self-assembly of the Pd2L4 capsule composed of bent ligands with anthracene panels tends to produce large intermediates containing more components than the capsule. This is ascribed to steric interactions between the panels.Bending New Corners: The introduction of anthracene panels in a bent ditopic ligand alters the self-assembly pathway of the Pd2L4 complex, transiently producing large intermediates containing more components than the capsule. This effect can be ascribed to steric interactions between the neighboring panels.
      PubDate: 2018-01-17T08:10:55.622051-05:
      DOI: 10.1002/chem.201705253
  • Direct Reductive N-Functionalization of Aliphatic Nitro Compounds
    • Authors: Marian Rauser; Christoph Ascheberg, Meike Niggemann
      Pages: 3970 - 3974
      Abstract: The first general protocol for the direct reductive N-functionalization of aliphatic nitro compounds is presented. The nitro group is partially reduced to a nitrenoid, with a mild and readily available combination of B2pin2 and zinc organyls. Thereby, the formation of an unstable nitroso intermediate is avoided, which has so far severely limited reductive transformations of aliphatic nitro compounds. The reaction is concluded by an electrophilic amination of zinc organyls.No N=O! The first general protocol for a direct reductive N-functionalization of aliphatic nitro compounds is presented. This type of transformation was so far limited to nitro compounds devoid of α-protons, due to the fast nitroso-oxime tautomerization. N-functionalization is enabled by an alternative reaction path via a more stable nitrenoid intermediate.
      PubDate: 2018-02-21T03:31:07.497051-05:
      DOI: 10.1002/chem.201705986
  • Interfacial Generation of a Carbanion: The Key Step of PTC Reaction
           Directly Observed by Second Harmonic Generation
    • Authors: Michal Hamkalo; Piotr Fita, Michal Fedorynski, Mieczyslaw Makosza
      Pages: 3975 - 3979
      Abstract: We present the first unambiguous evidence of the interfacial mechanism of phase-transfer catalysis (PTC) by direct observation of the formation of carbanions in the interfacial region between the aqueous and the organic phase by using a surface-sensitive spectroscopic method known as second harmonic generation (SHG). Ion exchange of carbanions adsorbed at the surface after addition of lipophilic tetraalkylammonium salts (TAA) to organic phase and transport of the lipophilic ion-pairs to the organic phase is observed. Results allow for the formulation of a more detailed mechanism of PTC.Carbanions are created only at the interface between organic and aqueous phases. A second harmonic (SH) beam is generated only by these carbanions.
      PubDate: 2018-02-21T08:56:38.058348-05:
      DOI: 10.1002/chem.201705597
  • Zinc-Containing Radical Anions via Single Electron Transfer to
           Donor–Acceptor Adducts
    • Authors: Levy L. Cao; Karlee L. Bamford, Liu Leo Liu, Douglas W. Stephan
      Pages: 3980 - 3983
      Abstract: Reactions of [Cp*2Fe] with the Lewis acid [Zn(C6F5)2] in the presence of [(PhC(S)S)2], 9,10-phenanthrenedione or 4,5-pyrenedione yield the salt [Cp*2Fe][(PhC(S)S)Zn(C6F5)2] 1, [Cp*2Fe][((C14H8O2)Zn(C6F5)2)⋅] 4, and [Cp*2Fe][((C16H8O2)Zn(C6F5)2)⋅] 5, respectively. The latter two species represent the first examples of isolable zinc-containing radical anions. While [(PhC(S)S)2] binds weakly to [Zn(C6F5)2], the diones afford the isolable adducts [(C14H8O2)Zn(C6F5)2] 2 and [(C16H8O2)Zn(C6F5)2] 3. Cyclic voltammetry and computational studies support the view that 4 and 5 are formed via single electron transfer (SET) to the donor–acceptor adducts, 2 and 3, respectively. Subsequent treatment of 4 and 5 with [NC5H4NMe2] affords [Zn(C6F5)2(NC5H4NMe2)2] with liberation of the dione, and regeneration of [Cp*2Fe].Radical anions containing Zn…: SET reactions previously established for main group systems are extended to d-block species yielding the first examples of zinc-containing radical anions salts, [Cp*2Fe] [(C14H8O2)Zn(C6F5)2)⋅] 4, and [Cp*2Fe][(C16H8O2)Zn(C6F5)2)⋅] 5.
      PubDate: 2018-02-27T07:10:33.936886-05:
      DOI: 10.1002/chem.201800607
  • Arene-Ligand-Free Ruthenium(II/III) Manifold for meta-C−H Alkylation:
           Remote Purine Diversification
    • Authors: Fernando Fumagalli; Svenja Warratz, Shou-Kun Zhang, Torben Rogge, Cuiju Zhu, A. Claudia Stückl, Lutz Ackermann
      Pages: 3984 - 3988
      Abstract: meta-Selective C−H alkylations of bioactive purine derivatives were accomplished by versatile ruthenium catalysis. Thus, the arene-ligand-free complex [Ru(OAc)2(PPh3)2] enabled remote C−H functionalizations with ample scope and excellent levels of chemo- and positional selectivities. Detailed experimental and computational mechanistic studies provided strong support for a facile C−H activation within a ruthenium(II/III) manifold.Pur(in)e remote: meta-C−H alkylations were accomplished on sensitive purine nucleosides by an arene-ligand-free ruthenium catalyst with ample scope.
      PubDate: 2018-02-21T07:15:52.711989-05:
      DOI: 10.1002/chem.201800530
  • Equilibration of Imine-Linked Polymers to Hexagonal Macrocycles Driven by
    • Authors: Anton D. Chavez; Austin M. Evans, Nathan C. Flanders, Ryan P. Bisbey, Edon Vitaku, Lin X. Chen, William R. Dichtel
      Pages: 3989 - 3993
      Abstract: Macrocycles based on directional bonding and dynamic covalent bond exchange can be designed with specific pore shapes, sizes, and functionality. These systems retain many of the design criteria and desirable aspects of two-dimensional (2D) covalent organic frameworks (COFs) but are more easily processed. Here we access discrete hexagonal imine-linked macrocycles by condensing a truncated analogue of 1,3,5-tris(4-aminophenyl)benzene (TAPB) with terephthaldehyde (PDA). The monomers first condense into polymers but eventually convert into hexagonal macrocycles in high yield. The high selectivity for hexagonal macrocycles is enforced by their aggregation and crystallization into layered structures with more sluggish imine exchange. Their formation and exchange processes provide new insight into how imine-linked 2D COF simultaneously polymerize and crystallize. Solutions of these assembled macrocycles were cast into oriented, crystalline films, expanding the potential routes to 2D materials.Stuck in the stacks: Trigonal diamines condensed with linear dialdehydes provide discrete macrocycles that are structurally similar to two-dimensional covalent organic frameworks (COFs). Analogous to their COF counterparts, the monomers first form linear polymers, which overtime convert exclusively into hexagonal macrocycles that aggregate into layered structures, slowing the kinetics of imine exchange.
      PubDate: 2018-02-26T03:02:40.170021-05:
      DOI: 10.1002/chem.201800459
  • Total Synthesis of Parvineostemonine by Structure Pattern Recognition: A
           Unified Approach to Stemona and Sarpagine Alkaloids
    • Authors: Christa K. G. Gerlinger; Sebastian Krüger, Tanja Gaich
      Pages: 3994 - 3997
      Abstract: Through structure pattern recognition based total synthesis we designed a synthesis in which two biogenetically unrelated natural product families (Stemona- and Sarpagine alkaloids) share 50 % of their synthetic sequence. In this report, the efficiency of such a strategic approach is demonstrated in the total synthesis of the Stemona alkaloid parvineostemonine, proceeding through a privileged intermediate that we have previously transformed into biogenetically completely unrelated Sarpagine alkaloids. In addition, we capitalized on the symmetry properties of the privileged intermediate, which was obtained as two regioisomers. After their separation by column chromatography the two regioisomers were converted to the corresponding pair of enantiomers by one transformation. To the best of our knowledge, this feature (conversion of regioisomers to enantiomers) has never been applied to natural product synthesis, and proved to be very valuable, since it allowed to obtain both optical antipodes of parvineostemonine in a single synthetic campaign. This not only enabled the determination of the previously undisclosed absolute configuration of the natural product, but gave 60–200 mg amounts of both enantiomers of the natural product.The absolute configuration of the Stemona alkaloid parvineostemonine was elucidated by total synthesis. The synthetic strategy allows for a short and efficient access in eight steps from known building blocks and 12 steps from commercial starting materials. The synthetic route provides acceptable amounts of the natural product (70–200 mg). In the course of the synthesis both regioisomers produced in the [5+2]-cycloaddition can be carried through due to the symmetry of the final product. These regioisomers are converted into the corresponding enantiomers by a Raney-Nickel reduction, and thus deliver both optical antipodes of parvineostemonine in one synthetic campaign.
      PubDate: 2018-02-16T05:56:12.178433-05:
      DOI: 10.1002/chem.201800365
  • Brønsted Base-Catalyzed Umpolung Intramolecular Cyclization of
           Alkynyl Imines
    • Authors: Azusa Kondoh; Masahiro Terada
      Pages: 3998 - 4001
      Abstract: A novel “umpolung” intramolecular cyclization of alkynyl imines, in which the electrophilic imine sp2-carbon formally serves as a nucleophilic site, was developed under Brønsted base catalysis. The reaction involves the unprecedented catalytic generation of α-aminoester enolates from α-iminoesters via the 1,2-addition of the anion of a secondary phosphite to an imine moiety followed by the [1,2]-rearrangement of a dialkoxyphosphoryl moiety from carbon to nitrogen, which is a formal umpolung process, and the intramolecular addition to an alkyne. This is a rare example of a [1,2]-rearrangement of a dialkoxyphosphoryl moiety from carbon to nitrogen to generate an α-amino carbanion and the first catalytic carbon–carbon bond forming reaction utilizing the resulting carbanion as a nucleophile.A novel “umpolung” intramolecular cyclization of alkynyl imines, in which the electrophilic imine sp2-carbon formally serves as a nucleophilic site, was developed under Brønsted base catalysis. This is a rare example of a [1,2]-rearrangement of a dialkoxyphosphoryl moiety from carbon to nitrogen to generate an α-amino carbanion and the first catalytic carbon–carbon bond-forming reaction utilizing the resulting carbanion as a nucleophile.
      PubDate: 2018-02-16T05:56:29.719369-05:
      DOI: 10.1002/chem.201800219
  • Self-Assembly of a Guanosine Derivative To Form Nanostructures and
           Transmembrane Channels
    • Authors: Rabindra Nath Das; Y. Pavan Kumar, S. Arun Kumar, Ole Mathis Schütte, Claudia Steinem, Jyotirmayee Dash
      Pages: 4002 - 4005
      Abstract: We herein report the self-assembly of a lipophilic bromoguanosine derivative (G1) in homogeneous solution, in the solid state and in planar bilayer membranes. The self-assembly of G1, driven by H-bonding and π–π stacking interactions can form different nano-structures depending on incubation time. The G1 nanostructure is able to bind a bioactive dye like Rose Bengal. In crystal state, it shows ribbon type H-bonding pattern and exhibits birefringence in polarized light. And further, the self-assembled nanostructure of G1 can form discrete transmembrane ion channels in lipid bilayer membranes, enabling passage of potassium ions.Nucleoside nanostructure and ion channel: A simple lipophilic nucleoside analogue forms self-assembled structures in solution, solid state and in lipid bilayer. Interestingly, the self-assembled structure of this nucleoside exhibits birefringence, incorporates a bioactive dye and forms transmembrane ion channels across a phospholipid bilayer.
      PubDate: 2018-02-19T09:21:44.32042-05:0
      DOI: 10.1002/chem.201800205
  • Controlling Photoconductivity in PBI Films by Supramolecular Assembly
    • Authors: Emily R. Draper; Lewis J. Archibald, Michael C. Nolan, Ralf Schweins, Martijn A. Zwijnenburg, Stephen Sproules, Dave J. Adams
      Pages: 4006 - 4010
      Abstract: Perylene bisimides (PBIs) self-assemble in solution. The solubility of the PBIs is commonly changed through the choice of substituents at the imide positions. It is generally assumed this substitution does not affect the electronic properties of the PBI, and that the properties of the self-assembled aggregate are essentially that of the isolated molecule. However, substituents do affect the self-assembly, resulting in potentially different packing in the formed aggregates. Here, we show that the photoconductivity of films formed from a library of substituted PBIs varies strongly with the substituent and demonstrate that this is due to the different ways in which they pack. Our results open the possibility for tuning the optoelectronic properties of self-assembled PBIs by controlling the aggregate structure through careful choice of substituent, as demonstrated by us here optimising the photoconductivity of PBI films in this way.The photoconductivity of films formed from self-assembled perylene bisimides varies strongly with the amino acid substituent at the imide position. The substituent controls the molecular packing, and this leads to the differences.
      PubDate: 2018-02-19T09:27:31.554252-05:
      DOI: 10.1002/chem.201800201
  • Complexes of Stiboranium Mono-, Di-, and Trications
    • Authors: Christopher Frazee; Neil Burford, Robert McDonald, Michael J. Ferguson, Andreas Decken, Brian O. Patrick
      Pages: 4011 - 4013
      Abstract: Reaction of Ph2SbCl3 with 2,2′-bipyridine and Me3SiOSO2CF3 releases chlorobenzene, which is interpreted as a reductive (SbV/SbIII) elimination from a complex of a stiboranium cation. Conversely, reactions of Ph2SbCl3 with 4-methylpyridine-N-oxide and AgOSO2CF3 give redox-resistant complexes with the generic formulae [Ph2SbCl3−xLx+1][OTf]x, including a compound containing a pnictogen(V) trication.Diverse redox chemistry: A series of SbV complexes with the generic formula [Ph2SbCl3−xLx+1][OTf]x (L=OPyrMe) has been prepared by chloride-ion abstraction in the presence of a ligand and characterized, including the first structural characterization of a PnV trication.
      PubDate: 2018-02-23T05:20:40.14839-05:0
      DOI: 10.1002/chem.201800196
  • Streamlined Synthesis and Evaluation of Teichoic Acid Fragments
    • Authors: Daan van der Es; Francesca Berni, Wouter F. J. Hogendorf, Nico Meeuwenoord, Diana Laverde, Angela van Diepen, Herman S. Overkleeft, Dmitri V. Filippov, Cornelis H. Hokke, Johannes Huebner, Gijsbert A. van der Marel, Jeroen D. C. Codée
      Pages: 4014 - 4018
      Abstract: Teichoic acids (TAs) are key components of the Gram-positive bacterial cell wall that are composed of alditol phosphate repeating units, decorated with alanine or carbohydrate appendages. Because of their microhetereogeneity, pure well-defined TAs for biological or immunological evaluation cannot be obtained from natural sources. We present here a streamlined automated solid-phase synthesis approach for the rapid generation of well-defined glycosylated, glycerol-based TA oligomers. Building on the use of a “universal” linker system and fluorous tag purification strategy, a library of glycerolphosphate pentadecamers, decorated with various carbohydrate appendages, is generated. These are used to create a structurally diverse TA-microarray, which is used to reveal, for the first time, the binding preferences of anti-LTA (lipoteichoic acids) antibodies at the molecular level.Using a streamlined, automated solid-phase synthetic approach, well-defined glycosylated, glycerol-based teichoic acid oligomers were synthesized. These are used to create a structurally diverse teichoic acid microarray, which is used to reveal, for the first time, the binding preferences of anti-LTA antibodies at the molecular level.
      PubDate: 2018-02-19T03:03:54.612122-05:
      DOI: 10.1002/chem.201800153
  • A Novel Reconfigurable Logic Unit Based on the DNA-Templated
           Potassium-Concentration-Dependent Supramolecular Assembly
    • Authors: Chunrong Yang; Dan Zou, Jianchi Chen, Linyan Zhang, Jiarong Miao, Dan Huang, Yuanyuan Du, Shu Yang, Qianfan Yang, Yalin Tang
      Pages: 4019 - 4025
      Abstract: Plenty of molecular circuits with specific functions have been developed; however, logic units with reconfigurability, which could simplify the circuits and speed up the information process, are rarely reported. In this work, we designed a novel reconfigurable logic unit based on a DNA-templated, potassium-concentration-dependent, supramolecular assembly, which could respond to the input stimuli of H+ and K+. By inputting different concentrations of K+, the logic unit could implement three significant functions, including a half adder, a half subtractor, and a 2-to-4 decoder. Considering its reconfigurable ability and good performance, the novel prototypes developed here may serve as a promising proof of principle in molecular computers.It′s logical captain! A multifunctional logic unit based on a DNA-templated potassium-concentration-dependent supramolecular assembly was constructed to implement three significant logic functions, including a half adder (HA), a half subtractor (HS) and a decoder (DC).
      PubDate: 2018-01-31T12:02:57.177485-05:
      DOI: 10.1002/chem.201704824
  • Brønsted Acid-Catalyzed Tandem Cyclizations of Tryptamine-Ynamides
           Yielding 1H-Pyrrolo[2,3-d]carbazole Derivatives
    • Authors: Yanshi Wang; Jingsheng Lin, Xiaoyu Wang, Guanghui Wang, Xinhang Zhang, Bo Yao, Yuandong Zhao, Pengfei Yu, Bin Lin, Yongxiang Liu, Maosheng Cheng
      Pages: 4026 - 4032
      Abstract: Ynamides, as versatile synthetic precursors, have attracted much attention from synthetic chemists and sparked the development of a number of methodologies for the construction of various structures. 1H-Pyrrolo[2,3-d]carbazole is a core scaffold of a series of monoterpene indole alkaloids found in Kopsia, Strychnos, and Aspidosperma, for example. In this study, 1H-pyrrolo[2,3-d]carbazole derivatives were synthesized by a Brønsted acid-catalyzed tandem cyclization starting from tryptamine-based ynamides. This strategy prevented Wagner–Meerwein rearrangement by instantaneous intramolecular nucleophilic trapping of the indoleninium to afford a tetracyclic indoline via an in situ-formed enol species induced by the formation of a more stable conjugate diene moiety. The functional group tolerances were investigated by using a series of readily available substrates. A plausible mechanism has been proposed based on the evidence of the capture of the hemiaminal intermediate. Lastly, a Büchi ketone, which is the pivotal intermediate in the synthesis of the indole alkaloid vindorosine, was synthesized by utilizing our newly developed methodology.Tandem cycling: A two-step transformation leading to the synthesis of 1H-pyrrolo[2,3-d]carbazole derivatives starting from tryptamine-based ynamides has been developed and applied to the formal synthesis of vindorosine (see scheme). A plausible mechanism for this tandem cyclization was probed by capturing the reaction intermediate.
      PubDate: 2018-01-10T05:45:39.124141-05:
      DOI: 10.1002/chem.201705189
  • Safe-by-Design Ligand-Coated ZnO Nanocrystals Engineered by an
           Organometallic Approach: Unique Physicochemical Properties and Low
           Toxicity toward Lung Cells
    • Authors: Małgorzata Wolska-Pietkiewicz; Katarzyna Tokarska, Agnieszka Grala, Anna Wojewódzka, Elżbieta Chwojnowska, Justyna Grzonka, Piotr J. Cywiński, Krzysztof Kruczała, Zbigniew Sojka, Michał Chudy, Janusz Lewiński
      Pages: 4033 - 4042
      Abstract: The unique physicochemical properties and biocompatibility of zinc oxide nanocrystals (ZnO NCs) are strongly dependent on the nanocrystal/ligand interface, which is largely determined by synthetic procedures. Stable ZnO NCs coated with a densely packed shell of 2-(2-methoxyethoxy)acetate ligands, which act as miniPEG prototypes, with average core size and hydrodynamic diameter of 4–5 and about 12 nm, respectively, were prepared by an organometallic self-supporting approach, fully characterized, and used as a model system for biological studies. The ZnO NCs from the one-pot, self-supporting organometallic procedure exhibit unique physicochemical properties such as relatively high quantum yield (up to 28 %), ultralong photoluminescence decay (up to 2.1 μs), and EPR silence under standard conditions. The cytotoxicity of the resulting ZnO NCs toward normal (MRC-5) and cancer (A549) human lung cell lines was tested by MTT assay, which demonstrated that these brightly luminescent, quantum-sized ZnO NCs have a low negative impact on mammalian cell lines. These results substantiate that the self-supporting organometallic approach is a highly promising method to obtain high-quality, nontoxic, ligand-coated ZnO NCs with prospective biomedical applications.Small but safe: A one-pot, self-supporting organometallic approach was used to synthesize stable ZnO nanocrystals (NCs) with a densely packed shell of 2-(2-methoxyethoxy)acetate ligands (see figure) as a model system for toxicological studies. These brightly luminescent ZnO NCs exhibit low toxicity, despite their small average core diameter of 4–5 nm, ultralong-lived luminescence, and EPR silence.
      PubDate: 2018-01-17T11:36:38.346157-05:
      DOI: 10.1002/chem.201704207
  • Isomerization of Allylic Alcohols to Ketones Catalyzed by Well-Defined
           Iron PNP Pincer Catalysts
    • Authors: Tian Xia; Zhihong Wei, Brian Spiegelberg, Haijun Jiao, Sandra Hinze, Johannes G. de Vries
      Pages: 4043 - 4049
      Abstract: [Fe(PNP)(CO)HCl] (PNP=di-(2-diisopropylphosphanyl-ethyl)amine), activated in situ with KOtBu, is a highly active catalyst for the isomerization of allylic alcohols to ketones without an external hydrogen supply. High reaction rates were obtained at 80 °C, but the catalyst is also sufficiently active at room temperature with most substrates. The reaction follows a self-hydrogen-borrowing mechanism, as verified by DFT calculations. An alternative isomerization through alkene insertion and β-hydride elimination could be excluded on the basis of a much higher barrier. In alcoholic solvents, the ketone product is further reduced to the saturated alcohol.A borrowing pincer: The isomerization of non-activated allylic alcohols to ketones catalyzed by an iron(II) PNP pincer complex (see graphic) is reported. High reaction rates have been achieved, even at room temperature. A self-borrowing hydrogen mechanism has been established on the basis of DFT calculations.
      PubDate: 2018-01-16T03:25:40.082194-05:
      DOI: 10.1002/chem.201705454
  • One-Carbon Oxidative Annulations of 1,3-Enynes by Catalytic C−H
           Functionalization and 1,4-Rhodium(III) Migration
    • Authors: Johnathon D. Dooley; Hon Wai Lam
      Pages: 4050 - 4054
      Abstract: Rhodium(III)-catalyzed C−H functionalization-oxidative annulations of aromatic substrates with 1,3-enynes that contain allylic hydrogen atoms cis to the alkyne are described. The key step in these reactions is an alkenyl-to-allyl 1,4-rhodium(III) migration to give electrophilic π-allylrhodium(III) species. Nucleophilic trapping of these species gives heterocycles such as benzopyrans, isobenzofuranones, and isoindolinones.Can't wait to migrate: Rhodium(III)-catalyzed C−H functionalization–oxidative annulations of aromatic substrates with 1,3-enynes that contain allylic hydrogen atoms cis to the alkyne are described. The key step in these reactions is an alkenyl-to-allyl 1,4-rhodium(III) migration to give electrophilic π-allylrhodium(III) species, which are trapped to give benzopyrans, isobenzofuranones, and isoindolinones.
      PubDate: 2018-02-21T07:20:55.093704-05:
      DOI: 10.1002/chem.201706043
  • Synthesis of α-l-Fucopyranoside-Presenting Glycoclusters and
           Investigation of Their Interaction with Photorhabdus asymbiotica Lectin
    • Authors: Gita Jančaříková; Mihály Herczeg, Eva Fujdiarová, Josef Houser, Katalin E. Kövér, Anikó Borbás, Michaela Wimmerová, Magdolna Csávás
      Pages: 4055 - 4068
      Abstract: Photorhabdus asymbiotica is a gram-negative bacterium that is not only as effective an insect pathogen as other members of the genus, but it also causes serious diseases in humans. The recently identified lectin PHL from P. asymbiotica verifiably modulates an immune response of humans and insects, which supports the idea that the lectin might play an important role in the host–pathogen interaction. Dimeric PHL contains up to seven l-fucose-specific binding sites per monomer, and in order to target multiple binding sites of PHL, α-l-fucoside-containing di-, tri- and tetravalent glycoclusters were synthesized. Methyl gallate and pentaerythritol were chosen as multivalent scaffolds, and the fucoclusters were built from the above-mentioned cores by coupling with different oligoethylene bridges and propargyl α-l-fucosides using 1,3-dipolar azide-alkyne cycloaddition. The interaction between fucoside derivates and PHL was investigated by several biophysical and biological methods, ITC and SPR measurements, hemagglutination inhibition assay, and an investigation of bacterial aggregation properties were carried out. Moreover, details of the interaction between PHL and propargyl α-l-fucoside as a monomer unit were revealed using X-ray crystallography. Besides this, the interaction with multivalent compounds was studied by NMR techniques. The newly synthesized multivalent fucoclusters proved to be up to several orders of magnitude better ligands than the natural ligand, l-fucose.Focus on Fucose: A novel class of α-l-fucopyranoside-presenting glycoclusters have been synthesized to target multiple binding sites of PHL lectin from Photorhabdus asymbiotica. The interaction between fucosides and PHL was investigated by biological methods, X-ray crystallography and saturation transfer difference NMR (STD-NMR). The potency of ligands depended on their valency and architecture, but all fucoclusters proved to be up to several orders of magnitude better ligands than its natural ligand, l-fucose.
      PubDate: 2018-02-19T09:27:14.710674-05:
      DOI: 10.1002/chem.201705853
  • Formation of Cyanamide–Glyoxal Oligomers in Aqueous Environments
           Relevant to Primeval and Astrochemical Scenarios: A Spectroscopic and
           Theoretical Study
    • Authors: Nieves Lavado; Juan García de la Concepción, Reyes Babiano, Pedro Cintas
      Pages: 4069 - 4085
      Abstract: The condensation of cyanamide and glyoxal, two well-known prebiotic monomers, in an aqueous phase has been investigated in great detail, demonstrating the formation of oligomeric species of varied structure, though consistent with generalizable patterns. This chemistry involving structurally simple substances also illustrates the possibility of building molecular complexity under prebiotically plausible conditions, not only on Earth, but also in extraterrestrial scenarios. We show that cyanamide–glyoxal reactions in water lead to mixtures comprising both acyclic and cyclic fragments, largely based on fused five- and six-membered rings, which can be predicted by computation. Remarkably, such a mixture could be identified using high-resolution electrospray ionization (ESI) mass spectrometry and spectroscopic methods. A few mechanistic pathways can be postulated, most involving the intermediacy of glyoxal cyanoimine and further chain growth, thus increasing the diversity of the observed products. This rationale is supported by theoretical analyses with clear-cut identification of all of the stationary points and transition-state structures. The properties and structural differences of oligomers obtained under thermodynamic conditions in water as opposed to those isolated by precipitation from organic media are also discussed.Complex, not messy! Organic matter detected in extraterrestrial bodies might not be as intractable as thought. Prebiotic simulations with simple monomers provide clues to regular structural patterns obtained in aqueous environments (see graphic).
      PubDate: 2018-02-19T09:00:38.630738-05:
      DOI: 10.1002/chem.201705747
  • A Unique (3+2) Annulation Reaction between Meldrum's Acid and Nitrones:
           Mechanistic Insight by ESI-IMS-MS and DFT Studies
    • Authors: Nicolas Lespes; Etienne Pair, Clisy Maganga, Marie Bretier, Vincent Tognetti, Laurent Joubert, Vincent Levacher, Marie Hubert-Roux, Carlos Afonso, Corinne Loutelier-Bourhis, Jean-François Brière
      Pages: 4086 - 4093
      Abstract: The fragile intermediates of the domino process leading to an isoxazolidin-5-one, triggered by unique reactivity between Meldrum's acid and an N-benzyl nitrone in the presence of a Brønsted base, were determined thanks to the softness and accuracy of electrospray ionization mass spectrometry coupled to ion mobility spectrometry (ESI-IMS-MS). The combined DFT study shed light on the overall organocatalytic sequence that starts with a stepwise (3+2) annulation reaction that is followed by a decarboxylative protonation sequence encompassing a stereoselective pathway issue.Stuck in the middle: The intermediates of the domino process leading to an isoxazolidin-5-one, triggered by unique reactivity between Meldrum's acid and an N-benzyl nitrone in the presence of a Brønsted base, are determined thanks to the off-line ESI-IMS-MS technique. A combined DFT study sheds light on the overall organocatalytic pathway that starts by a stepwise (3+2) annulation reaction and is followed by a decarboxylative protonation sequence (see scheme).
      PubDate: 2018-02-15T07:45:37.809649-05:
      DOI: 10.1002/chem.201705714
  • Natural Deposition Strategy for Interfacial, Self-Assembled, Large-Scale,
           Densely Packed, Monolayer Film with Ligand-Exchanged Gold Nanorods for In
           Situ Surface-Enhanced Raman Scattering Drug Detection
    • Authors: Mei Mao; Binbin Zhou, Xianghu Tang, Cheng Chen, Meihong Ge, Pan Li, Xingjiu Huang, Liangbao Yang, Jinhuai Liu
      Pages: 4094 - 4102
      Abstract: Liquid interfacial self-assembly of metal nanoparticles holds great promise for its various applications, such as in tunable optical devices, plasmonics, sensors, and catalysis. However, the construction of large-area, ordered, anisotropic, nanoparticle monolayers and the acquisition of self-assembled interface films are still significant challenges. Herein, a rapid, validated method to fabricate large-scale, close-packed nanomaterials at the cyclohexane/water interface, in which hydrophilic cetyltrimethylammonium bromide coated nanoparticles and gold nanorods (AuNRs) self-assemble into densely packed 2D arrays by regulating the surface ligand and suitable inducer, is reported. Decorating AuNRs with polyvinylpyrrolidone not only extensively decreases the charge of AuNRs, but also diminishes repulsive forces. More importantly, a general, facile, novel technique to transfer an interfacial monolayer through a designed in situ reaction cell linked to a microfluidic chip is revealed. The self-assembled nanofilm can then automatically settle on the substrate and be directly detected in the reaction cell in situ by means of a portable Raman spectrometer. Moreover, a close-packed monolayer of self-assembled AuNRs provides massive, efficient hotspots to create great surface-enhanced Raman scattering (SERS) enhancement, which provides high sensitivity and reproducibility as the SERS-active substrate. Furthermore, this strategy was exploited to detect drug molecules in human urine for cyclohexane-extracted targets acting as the oil phase to form an oil/water interface. A portable Raman spectrometer was employed to detect methamphetamine down to 100 ppb levels in human urine, exhibiting excellent practicability. As a universal platform, handy tool, and fast pretreatment method with a good capability for drug detection in biological systems, this technique shows great promise for rapid, credible, and on-spot drug detection.Detection between the layers: Anisotropic gold nanorods have been self-assembled at a liquid/liquid interface and used as a surface-enhanced Raman scattering (SERS) platform for the sensitive detection of methamphetamine in human urine (see figure).
      PubDate: 2018-02-16T06:42:59.299808-05:
      DOI: 10.1002/chem.201705700
  • On the Variable Reactivity of Phosphine-Functionalized [Ge9] Clusters:
           Zintl Cluster-Substituted Phosphines or Phosphine-Substituted Zintl
    • Authors: Felix S. Geitner; Christoph Wallach, Thomas F. Fässler
      Pages: 4103 - 4110
      Abstract: The reaction of [(Ge9{Si(TMS)3}2PtBu2)]− with NHCMesCuCl yields [(Ge9{Si(TMS)3}2)(tBu2P)]Cu(NHCMes) (1), which is a new derivative of the recently reported monomeric zwitterionic tetrel cluster compounds [(Ge9{Si(TMS)3}2)(tBu2P)]M(NHCDipp) (M: Cu, Ag, Au). By contrast, the reaction of the same anion [(Ge9{Si(TMS)3}2PtBu2)]− with the more labile copper phosphine complex Cy3PCuCl leads to the formation of [Ge9{Si(TMS)3}2{(tBu)2PCu}2Ge9{Si(TMS)3}2] (2), which is a neutral dimeric twofold-bridged [Ge9] cluster compound, with the exo-bonded phosphine substituent being involved in the cluster bridging. In case of the presence of sterically more demanding phosphines in [Ge9{Si(TMS)3}2PR2]− [R: Mes (3) and NiPr2 (4)], reactions with NHCDippCuCl yielded the complexes NHCDippCu[η3-Ge9{Si(TMS)3}2(PR2)] [R: Mes (5) and NiPr2 (6)], comprising exclusively Cu−Ge bonds. Compounds 5 and 6 show varying reactivity in dependence of the identity of the phosphine group and represent the first examples of fourfold-substituted [Ge9] clusters with three different ligands bound to the [Ge9] cluster core. All compounds were characterized by 1H, 13C, 31P, and 29Si NMR spectroscopy. Additionally, compounds 3 and 4 were analyzed by ESI-MS, and the structures of compounds 1, 2, and 5 were characterized by single-crystal X-ray diffraction.Ge-whiz: Derivatives of Ge9 Zintl cluster are accessible by introducing step-by-step silyl and phosphine substituents. The novel phosphine ligands introduce another reactive site. Reactions of [Ge9{Si(TMS)3}2PR2]− (R: tBu, Mes, and NiPr2) with different CuI organometallics reveal varying reactivity dependant on the bulkiness of the phosphine moieties and the stability of the applied CuI compounds. Syntheses of [(Ge9{Si(TMS)3}2)(tBu2P)]Cu(NHCMes), [Ge9{Si(TMS)3}2{(tBu)2PCu}2Ge9{Si(TMS)3}2] as well as NHCDippCu[η3-Ge9{Si(TMS)3}2(PR2)] (R: Mes and NiPr2) are reported.
      PubDate: 2018-02-16T06:00:44.834011-05:
      DOI: 10.1002/chem.201705678
  • Photocytotoxic Copper(II) Complexes with Schiff-Base Scaffolds for
           Photodynamic Therapy
    • Authors: Rong-Kai Lin; Chin-I Chiu, Cho-Han Hsu, Ying-Ju Lai, Parthiban Venkatesan, Po-Han Huang, Ping-Shan Lai, Chu-Chieh Lin
      Pages: 4111 - 4120
      Abstract: Photodynamic therapy (PDT) is a promising and minimally invasive method for the treatment of superficial diseases, and photosensitizers with high phototoxicity indices (defined as (IC50dark)/(IC50irradiation)) are essential for the development of ideal photosensitizing properties for this technology. Herein, we report a series of photocytotoxic copper(II) complexes [Cu(RQYMP)(dppn)] (RQYMP=N,N,O-tridentate Schiff-base derivatives, dppn=benzo[i]dipyrido[3,2-a;2′,3′-c]phenazine), the structures of which have been confirmed by mass spectrometry and FTIR spectroscopy. X-ray crystallography revealed that the CuN4O core of the [Cu(cumylQYMP)(dppn)](ClO4) complex (3) has a distorted square-pyramidal geometry. Phototoxicity indices of 329 against human squamous cell carcinoma (SCC15) and 296 against basal cell carcinoma (BCC) cell lines have been determined with [Cu(3-OMeQYMP)(dppn)](ClO4) (4). This can be attributed to the formation of reactive oxygen species, cell apoptosis, and caspase-3 activation, indicating high potential of complex 4 as a photosensitizer candidate in PDT. Thus, copper complexes bearing suitable Schiff-base ligands with a dppn co-ligand may be considered for the design of efficient metal-based anticancer agents for PDT.Copper complexes for PDT: Photocytotoxic copper(II) complexes [Cu(RQYMP)(dppn)] (RQYMP=N,N,O-tridentate Schiff-base derivatives, dppn=benzo[i]dipyrido[3,2-a;2′,3′-c]phenazine) show high phototoxicity indices against SCC15 and BCC cancer cells owing to the generation of reactive oxygen species and caspase-3-mediated cell apoptosis.
      PubDate: 2018-02-19T07:25:55.755886-05:
      DOI: 10.1002/chem.201705640
  • Influence of Flexibility on the Separation of Chiral Isomers in STW-Type
    • Authors: Rocio Bueno-Perez; Salvador R. G. Balestra, Miguel A. Camblor, Jung Gi Min, Suk Bong Hong, Patrick J. Merkling, Sofia Calero
      Pages: 4121 - 4132
      Abstract: Molecular simulation, through the computation of adsorption isotherms, is a useful predictive tool for the selective capacity of nanoporous materials. Generally, adsorbents are modelled as rigid frameworks, as opposed to allowing for vibrations of the lattice, and this approximation is assumed to have negligible impact on adsorption. In this work, this approach was tested in an especially challenging system by computing the adsorption of the chiral molecules 2-pentanol, 2-methylbutanol and 3-methyl-2-butanol in the all-silica and germanosilicate chiral zeolites STW and studying their lattice vibrations upon adsorption. The analysis of single- and multicomponent adsorption isotherms showed the suitability of STW-type zeolites as molecular sieves for chiral separation processes, which pose a challenging task in the chemical and pharmaceutical industries. Moreover, new experimental adsorption data validate the force field employed. The results reveal that the lattice vibrations of the all-silica framework are sorbate-independent, while those of germanosilicate STW show host–guest coupling modulated by uptake and sorbate type that disrupts the chiral recognition sites. This study indicates that the effects of intrinsic flexibility on the selective capacity of nanoporous materials may range from low to high impact, and some of them could not have been foreseen even after examination of the structural dynamics of an empty framework.Flexible frameworks: The adsorption of 2-pentanol (2P), 2-methylbutanol (2MB) and 3-methyl-2-butanol (3M2B) was investigated in all-silica and germanosilicate zeolites STW, and their lattice vibrations upon adsorption were studied. Regarding chiral selectivity, right-handed STW-Si is selective towards (R)-2P, whereas right-handed STW-SiGe is selective towards (S)-3M2B (see figure). The lattice vibrations of STW-Si are sorbate-independent, whereas those of STW-SiGe show host–guest coupling modulated by uptake and sorbate type that disrupts the chiral recognition sites.
      PubDate: 2018-02-19T08:55:54.199892-05:
      DOI: 10.1002/chem.201705627
  • Effect of Crystal Packing on the Thermosalient Effect of the Pincer-Type
           Diester Naphthalene-2,3-diyl-bis(4-fluorobenzoate): A New Class II
           Thermosalient Solid
    • Authors: Majid I. Tamboli; Durga Prasad Karothu, Mysore S. Shashidhar, Rajesh G. Gonnade, Panče Naumov
      Pages: 4133 - 4139
      Abstract: The pincer-like double ester naphthalene-2,3-diyl-bis(4-fluorobenzoate) (2) is pentamorphic. Upon heating crystals of form I to below their melting point (441–443 K), they undergo a phase transition accompanied by a thermosalient effect, that is, rare and visually striking motility whereby the crystals jump or disintegrate. The phase transition and the thermosalient effect are reversible. Analysis of the crystal structure revealed that form I is a class II thermosalient solid. Crystals of form III also underwent a reversible phase transition in the temperature range of 160 to 170 K; however, they were not thermosalient. Comparison of the structures and the mechanical responses of the two polymorphs revealed that the thermosalient effect of form I was due to reversible closing and opening of the arms of the diester molecules in a tweezer-like action.In top form: Form I of pentamorphic naphthalene-2,3-diyl-bis(4-fluorobenzoate) (2) undergoes a reversible phase transition to form IV followed by a thermosalient effect, whereby the crystals jump or burst. The effect is due to reversible closing and opening of the arms of the diester molecules in a tweezer-like action. Form III also undergoes a reversible phase transition; however, it is not thermosalient. Form II is a disappearing polymorph.
      PubDate: 2018-02-19T09:02:39.149743-05:
      DOI: 10.1002/chem.201705586
  • Aggregation Pathways of Native-Like Ubiquitin Promoted by Single-Point
           Mutation, Metal Ion Concentration, and Dielectric Constant of the Medium
    • Authors: Simona Fermani; Matteo Calvaresi, Vincenzo Mangini, Giuseppe Falini, Andrea Bottoni, Giovanni Natile, Fabio Arnesano
      Pages: 4140 - 4148
      Abstract: Ubiquitin-positive protein aggregates are biomarkers of neurodegeneration, but the molecular mechanism responsible for their formation and accumulation is still unclear. Possible aggregation pathways of human ubiquitin (hUb) promoted by both intrinsic and extrinsic factors, are here investigated. By a computational analysis, two different hUb dimers are indicated as possible precursors of amyloid-like structures, but their formation is disfavored by an electrostatic repulsion involving Glu16 and other carboxylate residues present at the dimer interface. Experimental data on the E16V mutant of hUb shows that this single-point mutation, although not affecting the overall protein conformation, promotes protein aggregation. It is sufficient to shift the same mutation by only two residues (E18V) to regain the behavior of wild-type hUb. The neutralization of Glu16 negative charge by a metal ion and a decrease of the dielectric constant of the medium by addition of trifluoroethanol (TFE), also promote hUb aggregation. The outcomes of this research have important implications for the prediction of physiological parameters that favor aggregate formation.Prefibrillar ubiquitin dimers: Ubiquitin dimers, with parallel (see figure, left) or antiparallel (right) alignment of edge β-strands, are indicated as possible precursors of amyloid structures. A computational analysis, complemented with experimental data, shows that the formation of such prefibrillar dimers is disfavored by electrostatic repulsion involving Glu16 and other carboxylate residues at the dimer interface.
      PubDate: 2018-02-21T07:26:10.894536-05:
      DOI: 10.1002/chem.201705543
  • 9,9′-Bifluorenylidene-Core Perylene Diimide Acceptors for As-Cast
           Non-Fullerene Organic Solar Cells: The Isomeric Effect on Optoelectronic
    • Authors: Yuan Zhao; Huan Wang, Shengpeng Xia, Feng Zhou, Zhenghui Luo, Jiajia Luo, Feng He, Chuluo Yang
      Pages: 4149 - 4156
      Abstract: Two different non-fullerene small-molecule acceptors, m-PIB and p-PIB, based on 9,9′-bifluorenylidene (BF) and perylene diimide (PDI) were designed and synthesized. Four β-substituted PDIs were linked to BF in different positions. Based on DFT analysis, derivative p-PIB exhibited reduced intramolecular twisting between the PDI moieties, more delocalized wave function, and sufficiently wider π-electron delocalization than that of m-PIB. The absorption ability of p-PIB was enhanced due to increased intermolecular interactions. By blending p-PIB with poly{4,8-bis[5-(2ethylhexyl)thiophen-2-yl]benzo[1,2-b:4,5-b′]dithiophene-co-3-fluorothieno[3,4-b]-thiophene-2-carboxylate} (PTB7-Th), organic solar cells (OSCs) based on p-PIB obtained a maximum power conversion efficiency of 5.95 % without any treatments. Due to the improved and balanced hole and electron mobilities, the short-circuit current and fill factor of OSCs based on PTB7-Th and p-PIB were significantly increased. The AFM and TEM results revealed that the PTB7-Th:p-PIB film had favorable nanoscale phase separation and formed a bicontinuous interpenetrating network.Core configuration: Isomeric effect on the optoelectronic properties of two small-molecule non-fullerene acceptors based on bifluorenylidene and perylene diimide were investigated. Organic solar cells based on these materials achieved the highest power conversion efficiency of 5.95 % without any treatments (see figure).
      PubDate: 2018-02-19T08:46:24.867453-05:
      DOI: 10.1002/chem.201705480
  • Purine-Derived Nitroxides for Noncovalent Spin-Labeling of Abasic Sites in
           Duplex Nucleic Acids
    • Authors: Nilesh R. Kamble; Snorri Th. Sigurdsson
      Pages: 4157 - 4164
      Abstract: A series of purine-based spin labels was prepared for noncovalent spin-labeling of abasic sites of duplex nucleic acids through hydrogen bonding to an orphan base on the opposing strand and π-stacking interactions with the flanking bases. Both 1,1,3,3-tetramethylisoindolin-2-yloxyl and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) were conjugated to either the C2- or C6-position of the purines, yielding nitroxide derivatives of guanine, adenine, or 2,6-diaminopurine. The isoindoline-derived spin labels showed extensive or full binding to abasic sites in RNA duplexes, whereas the TEMPO-derived spin labels showed limited binding. An adenine-derived spin label (5) bound fully at low temperature to abasic sites in both DNA and RNA duplexes when paired with thymine and uracil, respectively, complementing the previously described guanine-derived spin label Ǵ, which binds efficiently opposite cytosine. Compound Ǵ was also shown to bind to abasic sites in DNA–RNA hybrids, either in the DNA- or the RNA-strand. Ǵ showed only a minor flanking-sequence effect upon binding to abasic sites in RNA. When the abasic site was placed close to the end of the RNA duplex, the affinity of the spin label Ǵ was reduced; full binding was observed at the fourth position from the duplex end. In summary, spin labels 5 and Ǵ showed full binding to abasic sites in both DNA and RNA duplexes and are promising spin labels for structural studies of nucleic acids by pulsed EPR methods.Binding without bonding: Isoindoline-derived purine spin-labels bind efficiently to abasic sites of duplex DNA and RNA when they can form hydrogen bonds to the orphan base on the opposing strand; the adenine-derived spin label 5 pairs with uracil (or thymine) and the guanine-derivative Ǵ pairs with cytosine. The latter also binds to abasic sites in DNA–RNA hybrid duplexes and shows a minimal flanking-sequence effect upon binding to abasic sites in RNA.
      PubDate: 2018-02-16T06:00:37.617658-05:
      DOI: 10.1002/chem.201705410
  • Piecing it Together: An Additivity Scheme for Aromaticity using NICS-XY
    • Authors: Renana Gershoni-Poranne
      Pages: 4165 - 4172
      Abstract: Aromatic compounds are prevalent in both nature and man-made materials, yet their properties are still not fully understood and are therefore hard to predict. Herein, we introduce an additivity scheme for the prediction of the aromatic character of polycyclic aromatic hydrocarbons. Using a small set of building blocks and combination rules, we demonstrate the simple and intuitive construction of complete NICS-XY-scans for several test cases of one- and two-dimensional systems comprising six-membered rings. Partitioning the contribution of discrete building blocks provides insight into the aromatic character of these systems. The results obtained with this methodology provide a new perspective on the distribution of ring currents within polycyclic compounds and the effect of topology on the overall aromatic profile. The concept and strategy presented here are general and highly customizable. The scheme is easily applied to a wide range of interesting systems; it is especially beneficial for the investigation of large systems, as NICS-XY-scans are useful for their predictive utility with respect to optoelectronic and thermochemical properties.Piecing it together: The aromatic profiles of complex systems have been constructed from a small set of building blocks (see figure), thereby enabling rapid and simple prediction of their properties. The dissection to discrete contributions sheds light on the role of each building block and the topology of the system.
      PubDate: 2018-02-21T07:30:55.477873-05:
      DOI: 10.1002/chem.201705407
  • Direct, Metal-free C(sp2)−H Chalcogenation of Indoles and
           Imidazopyridines with Dichalcogenides Catalysed by KIO3
    • Authors: Jamal Rafique; Sumbal Saba, Marcelo S. Franco, Luana Bettanin, Alex R. Schneider, Lais T. Silva, Antonio L. Braga
      Pages: 4173 - 4180
      Abstract: Herein, we report a greener protocol for the synthesis of 3-Se/S-indoles and imidazo[1,2-a]pyridines through direct C(sp2)−H bond chalcogenation of heteroarenes with half molar equivalents of different dichalcogenides, using KIO3 as a non-toxic, easy-to-handle catalyst and a stoichiometric amount of glycerol. The reaction features are high yields, based on atom economy, easy performance on gram-scale, metal- and solvent-free conditions as well as applicability to different types of N-heteroarenes.The grass is greener: An efficient and scalable C(sp2)−H bond chalcogenation (Se/S) of 5-membered N-heterocyclic arenes, using KIO3 as a stable and easy-to-handle catalyst under solvent-free conditions, has been developed. Compared to other chalcogenation methods, this alternate system has significantly increased the substrate scope and avoids the use of non-stable and toxic catalyst.
      PubDate: 2018-01-25T07:57:23.475546-05:
      DOI: 10.1002/chem.201705404
  • Identification of the Minimal Glycotope of Streptococcus pneumoniae 7F
           Capsular Polysaccharide using Synthetic Oligosaccharides
    • Authors: Petra Ménová; Mauro Sella, Katrin Sellrie, Claney L. Pereira, Peter H. Seeberger
      Pages: 4181 - 4187
      Abstract: Streptococcus pneumoniae causes life-threatening diseases including meningitis, pneumonia and sepsis. Existing glycoconjugate vaccines based on purified capsular polysaccharides are widely used and help to prevent millions of deaths every year. Herein, the total syntheses of oligosaccharides resembling portions of the S. pneumoniae serotype 7F (ST7F) capsular polysaccharide repeating unit are reported. To define minimal glycan epitopes, glycan microarrays containing the synthetic oligosaccharides were used to screen human reference serum and revealed that both side chains of the ST7F play a key role in antigen recognition. The identification of protective minimal epitopes is vital to design efficient semi- and fully-synthetic glycoconjugate vaccines.Fighting pneumonia: Synthetic oligosaccharides resembling the Streptococcus pneumoniae serotype 7F capsular polysaccharide repeating unit were printed onto glycan microarrays. Screening of human reference serum helped to define minimal epitopes where both side chains on the central glycan are essential. Identification of protective minimal epitopes is key to the design of semi- and fully-synthetic glycoconjugate vaccines.
      PubDate: 2018-02-21T07:30:45.224191-05:
      DOI: 10.1002/chem.201705379
  • Enantioselective Brønsted Acid Catalysis as a Tool for the Synthesis of
           Natural Products and Pharmaceuticals
    • Authors: Jérémy Merad; Claudia Lalli, Guillaume Bernadat, Julien Maury, Géraldine Masson
      Pages: 3925 - 3943
      Abstract: Synthesis of biologically active molecules (whether at laboratory or industrial scale) remains a highly appealing area of modern organic chemistry. Nowadays, the need to access original bioactive scaffolds goes together with the desire to improve synthetic efficiency, while reducing the environmental footprint of chemical activities. Long neglected in the field of total synthesis, enantioselective organocatalysis has recently emerged as an environmentally friendly and indispensable tool for the construction of relevant bioactive molecules. Notably, enantioselective Brønsted acid catalysis has offered new opportunities in terms of both retrosynthetic disconnections and controlling stereoselectivity. The present report attempts to provide an overview of enantioselective total or formal syntheses designed around Brønsted acid-catalyzed transformations. To demonstrate the versatility of the reactions promoted and the diversity of the accessible motifs, this Minireview draws a systematic parallel between methods and retrosynthetic analysis. The manuscript is organized according to the main reaction types and the nature of newly-formed bonds.Chiral protons in action! Chiral Brønsted acids are versatile organocatalysts able to promote an outstanding range of enantioselective transformations. Beyond methodological considerations, this branch of catalysis is increasingly affecting the way of thinking about disconnections in total synthesis. The huge contribution of enantioselective Brønsted acid catalysis in setting up the chiral scaffold of elaborate bioactive molecules is highlighted in this Minireview.
      PubDate: 2017-12-04T07:41:23.820835-05:
      DOI: 10.1002/chem.201703556
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