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CHEMISTRY (656 journals)            First | 1 2 3 4 | Last

Showing 401 - 600 of 735 Journals sorted alphabetically
Journal of Porphyrins and Phthalocyanines     Hybrid Journal   (Followers: 2)
Journal of Pure and Applied Chemistry Research     Open Access   (Followers: 3)
Journal of Raman Spectroscopy     Hybrid Journal   (Followers: 17)
Journal of Research Updates in Polymer Science     Hybrid Journal   (Followers: 3)
Journal of Saudi Chemical Society     Open Access  
Journal of Solid State Chemistry     Hybrid Journal   (Followers: 14)
Journal of Solution Chemistry     Hybrid Journal   (Followers: 2)
Journal of Structural Chemistry     Hybrid Journal   (Followers: 1)
Journal of Sulfur Chemistry     Hybrid Journal   (Followers: 3)
Journal of Supercritical Fluids     Hybrid Journal   (Followers: 4)
Journal of Superhard Materials     Hybrid Journal   (Followers: 1)
Journal of Surface Science and Technology     Hybrid Journal  
Journal of Surfactants and Detergents     Hybrid Journal   (Followers: 3)
Journal of Taibah University for Science     Open Access   (Followers: 1)
Journal of the American Chemical Society     Hybrid Journal   (Followers: 374)
Journal of the American Society for Mass Spectrometry     Hybrid Journal   (Followers: 32)
Journal of the American Society of Brewing Chemists     Full-text available via subscription   (Followers: 3)
Journal of the Bangladesh Chemical Society     Open Access  
Journal of the Chilean Chemical Society     Open Access   (Followers: 2)
Journal of the Iranian Chemical Society     Hybrid Journal  
Journal of the Korean Society for Applied Biological Chemistry     Hybrid Journal   (Followers: 1)
Journal of the Mexican Chemical Society     Open Access   (Followers: 2)
Journal of the Serbian Chemical Society     Open Access  
Journal of the Turkish Chemical Society, Section A : Chemistry     Open Access  
Journal of Theoretical and Computational Chemistry     Hybrid Journal   (Followers: 10)
JPC - Journal of Planar Chromatography - Modern TLC     Full-text available via subscription   (Followers: 2)
Jurnal Inovasi Pendidikan Kimia     Open Access   (Followers: 5)
Jurnal Katalisator     Open Access  
Jurnal Kimia (Journal of Chemistry)     Open Access  
Jurnal Kimia Riset     Open Access  
Jurnal Penelitian Sains (JPS)     Open Access  
Karadeniz Chemical Science and Technology     Open Access  
Karbala International Journal of Modern Science     Open Access   (Followers: 3)
Kinetics and Catalysis     Hybrid Journal   (Followers: 5)
Konfigurasi : Jurnal Pendidikan Kimia dan Terapan     Open Access  
Korea-Australia Rheology Journal     Hybrid Journal  
Langmuir     Hybrid Journal   (Followers: 63)
Latvian Journal of Chemistry     Open Access   (Followers: 1)
Lebensmittelchemie     Hybrid Journal   (Followers: 1)
Lipid Insights     Open Access  
Luminescence     Hybrid Journal   (Followers: 5)
Macromolecular Materials & Engineering     Hybrid Journal   (Followers: 5)
Macromolecular Rapid Communications     Hybrid Journal   (Followers: 10)
Macromolecular Research     Hybrid Journal   (Followers: 2)
Macromolecular Symposia     Hybrid Journal   (Followers: 3)
Macromolecular Theory and Simulations     Hybrid Journal   (Followers: 2)
Macromolecules     Hybrid Journal   (Followers: 50)
Maghrebian Journal of Pure and Applied Science     Full-text available via subscription  
Magnetic Resonance in Chemistry     Hybrid Journal   (Followers: 10)
Magnetochemistry     Open Access  
Marine Chemistry     Hybrid Journal   (Followers: 7)
Marine Drugs     Open Access   (Followers: 4)
MATEC Web of Conferences     Open Access   (Followers: 5)
Materials Characterization     Hybrid Journal   (Followers: 34)
Materials Chemistry Frontiers     Full-text available via subscription  
Materials Horizons     Full-text available via subscription   (Followers: 3)
Materials Research Bulletin     Hybrid Journal   (Followers: 28)
Materials Science Monographs     Full-text available via subscription   (Followers: 3)
Materials Science-Poland     Open Access   (Followers: 1)
Materials Sciences and Applications     Open Access   (Followers: 3)
MedChemComm     Full-text available via subscription   (Followers: 7)
Medicinal Chemistry Research     Hybrid Journal   (Followers: 13)
Mediterranean Journal of Chemistry     Open Access  
Metallography, Microstructure, and Analysis     Hybrid Journal   (Followers: 2)
Metallomics     Full-text available via subscription  
Micro and Nano Systems Letters     Open Access   (Followers: 6)
Microchimica Acta     Hybrid Journal   (Followers: 2)
Microporous and Mesoporous Materials     Hybrid Journal   (Followers: 10)
Modern Chemistry & Applications     Open Access   (Followers: 1)
Modern Research in Catalysis     Open Access   (Followers: 1)
Molbank     Open Access   (Followers: 1)
Molecular Astrophysics     Full-text available via subscription  
Molecules     Open Access   (Followers: 7)
Molecules and Cells     Hybrid Journal   (Followers: 1)
Monatshefte für Chemie - Chemical Monthly     Hybrid Journal   (Followers: 4)
Mongolian Journal of Chemistry     Open Access  
Moroccan Journal of Chemistry     Open Access  
Moroccan Journal of Heterocyclic Chemistry     Open Access  
Moscow University Chemistry Bulletin     Hybrid Journal   (Followers: 1)
MRS Bulletin     Full-text available via subscription   (Followers: 4)
MRS Online Proceedings     Full-text available via subscription   (Followers: 1)
Nachrichten aus der Chemie     Hybrid Journal   (Followers: 17)
Nano Convergence     Open Access   (Followers: 1)
Nano Reviews & Experiments     Open Access   (Followers: 14)
Nanochemistry Research     Open Access  
Nanocontainers     Open Access   (Followers: 1)
Nanomaterials and the Environment     Open Access   (Followers: 1)
Nanoscale     Full-text available via subscription   (Followers: 20)
Nanoscale Advances     Open Access   (Followers: 1)
Nanoscale Research Letters     Open Access   (Followers: 9)
Nanoscience and Nanotechnology Letters     Full-text available via subscription   (Followers: 22)
Nanospectroscopy     Open Access   (Followers: 2)
Natural Product Reports     Full-text available via subscription   (Followers: 11)
Natural Products Chemistry & Research     Open Access   (Followers: 1)
Natural Products Journal     Hybrid Journal   (Followers: 1)
Natural Science     Open Access   (Followers: 9)
Natural Volatiles & Essential Oils     Open Access  
Nature Chemistry     Full-text available via subscription   (Followers: 95)
Nature Protocols     Full-text available via subscription   (Followers: 70)
Nature Reviews Chemistry     Hybrid Journal   (Followers: 7)
New Journal of Chemistry     Full-text available via subscription   (Followers: 19)
Nitric Oxide     Hybrid Journal  
Nitrogen     Open Access  
Nova Biotechnologica et Chimica     Open Access  
Nukleonika     Open Access   (Followers: 2)
Open Chemistry     Open Access   (Followers: 6)
Open Chemistry Journal     Open Access  
Open Conference Proceedings Journal     Open Access  
Open Journal of Composite Materials     Open Access   (Followers: 18)
Open Journal of Inorganic Non-metallic Materials     Open Access   (Followers: 4)
Open Journal of Medicinal Chemistry     Open Access   (Followers: 5)
Open Journal of Polymer Chemistry     Open Access   (Followers: 12)
Open Journal of Synthesis Theory and Applications     Open Access  
Open Medicinal Chemistry Journal     Open Access  
Orbital - The Electronic Journal of Chemistry     Open Access   (Followers: 3)
Organic & Biomolecular Chemistry     Full-text available via subscription   (Followers: 75)
Organometallics     Hybrid Journal   (Followers: 22)
Organosulfur Chemistry     Full-text available via subscription  
Oxidation of Metals     Hybrid Journal   (Followers: 18)
Peptidomics     Open Access  
Pharmaceuticals     Open Access   (Followers: 6)
Pharmaceutics     Open Access   (Followers: 4)
Phosphorus, Sulfur, and Silicon and the Related Elements     Hybrid Journal   (Followers: 2)
Photochemistry and Photobiology     Hybrid Journal   (Followers: 4)
Physical Sciences Reviews     Hybrid Journal   (Followers: 1)
Physics and Materials Chemistry     Open Access   (Followers: 2)
Phytochemistry     Hybrid Journal   (Followers: 6)
Phytochemistry Letters     Full-text available via subscription   (Followers: 4)
Plasma     Open Access   (Followers: 2)
Plasma Chemistry and Plasma Processing     Hybrid Journal   (Followers: 6)
Polímeros : Ciência e Tecnologia     Open Access  
Polycyclic Aromatic Compounds     Hybrid Journal  
Polyhedron     Hybrid Journal   (Followers: 4)
Polymer Chemistry     Full-text available via subscription   (Followers: 25)
Polymer Degradation and Stability     Hybrid Journal   (Followers: 26)
Polymer Engineering & Science     Hybrid Journal   (Followers: 16)
Polymer Reviews     Hybrid Journal   (Followers: 35)
Polymer Science Series D     Hybrid Journal   (Followers: 4)
Polymer Testing     Hybrid Journal   (Followers: 109)
Polymer-Plastics Technology and Engineering     Hybrid Journal   (Followers: 5)
Polymers     Open Access   (Followers: 18)
Procedia Chemistry     Open Access  
Proceedings in Radiochemistry. A Supplement to Radiochimica Acta     Open Access   (Followers: 1)
Proceedings of the Combustion Institute     Full-text available via subscription   (Followers: 8)
Processes     Open Access  
Progress in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 1)
Progress in Lipid Research     Hybrid Journal   (Followers: 3)
Progress in Organic Coatings     Hybrid Journal   (Followers: 9)
Progress in Polymer Science     Full-text available via subscription   (Followers: 37)
Progress in Reaction Kinetics and Mechanism     Full-text available via subscription   (Followers: 2)
Progress in Solid State Chemistry     Full-text available via subscription   (Followers: 3)
Progress in Surface Science     Full-text available via subscription   (Followers: 4)
Protein Science     Hybrid Journal   (Followers: 46)
Pure and Applied Chemistry     Hybrid Journal   (Followers: 8)
Química Nova     Open Access  
Quimica Viva     Open Access  
Radiochemistry     Hybrid Journal   (Followers: 2)
Rapid Communications in Mass Spectrometry     Hybrid Journal   (Followers: 32)
Reaction Chemistry & Engineering     Hybrid Journal  
Reaction Kinetics, Mechanisms and Catalysis     Hybrid Journal   (Followers: 2)
Recent Advances in Phytochemistry     Full-text available via subscription   (Followers: 3)
Recyclable Catalysis     Open Access   (Followers: 2)
Reports in Theoretical Chemistry     Open Access  
Research and Reports in Medicinal Chemistry     Open Access   (Followers: 3)
Research Journal of Phytochemistry     Open Access   (Followers: 3)
Review Journal of Chemistry     Hybrid Journal  
Reviews in Chemical Engineering     Hybrid Journal   (Followers: 6)
Reviews in Mineralogy and Geochemistry     Hybrid Journal   (Followers: 4)
Reviews of Adhesion and Adhesives     Full-text available via subscription  
Revista CENIC. Ciencias Quimicas     Open Access   (Followers: 2)
Revista Ciências Exatas e Naturais : RECEN     Open Access  
Revista Colombiana de Química     Open Access   (Followers: 1)
Revista Cubana de Química     Open Access  
Revista de Ciencia y Tecnología     Open Access  
Revista de Ciencias     Open Access  
Revista de la Societat Catalana de Química     Open Access  
Revista Debates em Ensino de Química     Open Access  
Revista ION     Open Access  
Revista Química : ciência, tecnologia e sociedade     Open Access  
RHAZES : Green and Applied Chemistry     Open Access  
RSC Advances     Open Access   (Followers: 33)
Rubber Chemistry and Technology     Full-text available via subscription   (Followers: 2)
Russian Chemical Reviews     Full-text available via subscription   (Followers: 4)
Russian Journal of Bioorganic Chemistry     Hybrid Journal   (Followers: 2)
Russian Journal of Coordination Chemistry     Hybrid Journal   (Followers: 1)
Russian Journal of General Chemistry     Hybrid Journal   (Followers: 1)
Russian Journal of Inorganic Chemistry     Hybrid Journal  
Sainstek : Jurnal Sains dan Teknologi     Open Access  
Science China Chemistry     Hybrid Journal   (Followers: 2)
Sciences & Technologie A : sciences exactes     Open Access  
Scientific Journal of Frontier Chemical Development     Open Access   (Followers: 1)
Scientific Reports     Open Access   (Followers: 73)
Sensors and Actuators B: Chemical     Hybrid Journal   (Followers: 17)
Separation & Purification Reviews     Hybrid Journal   (Followers: 8)
Separation Science and Technology     Hybrid Journal   (Followers: 14)
Separations     Open Access   (Followers: 6)
Silicon Chemistry     Hybrid Journal   (Followers: 2)
Smart Materials Research     Open Access   (Followers: 7)
Soft     Open Access  
Soft Nanoscience Letters     Open Access   (Followers: 2)

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Similar Journals
Journal Cover
Journal of the American Society for Mass Spectrometry
Journal Prestige (SJR): 1.058
Citation Impact (citeScore): 3
Number of Followers: 32  
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1044-0305 - ISSN (Online) 1879-1123
Published by Springer-Verlag Homepage  [2351 journals]
  • Bordetella bronchiseptica Glycosyltransferase Core Mutants Trigger Changes
           in Lipid A Structure
    • Abstract: Bordetella bronchiseptica, known to infect animals and rarely humans, expresses a lipopolysaccharide that plays an essential role in host interactions, being critical for early clearance of the bacteria. On a B. bronchiseptica 9.73 isolate, mutants defective in the expression of genes involved in the biosynthesis of the core region were previously constructed. Herein, a comparative detailed structural analysis of the expressed lipids A by MALDI-TOF mass spectrometry was performed. The Bb3394 LPS defective in a 2-amino-2-deoxy-d-galacturonic acid lateral residue of the core presented a penta-acylated diglucosamine backbone modified with two glucosamine phosphates, similar to the wild-type lipid A. In contrast, BbLP39, resulting in the interruption of the LPS core oligosaccharide synthesis, presented lipid A species consisting in a diglucosamine backbone N-substituted with C14:0(3-O-C12:0) in C-2 and C14:0(3-O-C14:0) in C-2′, O-acylated with C14:0(3-O-C10:0(3-OH) in C-3′ and with a pyrophosphate in C-1. Regarding Bb3398 also presenting a rough LPS, the lipid A is formed by a hexa-acylated diglucosamine backbone carrying one pyrophosphate group in C-1 and one phosphate in C-4′, both substituted with ethanolamine groups. As far as we know, this is the first description of a phosphoethanolamine modification in B. bronchiseptica lipid A. Our results demonstrate that although gene deletions were not directed to the lipid A moiety, each mutant presented different modifications. MALDI-TOF mass spectrometry was an excellent tool to highlight the structural diversity of the lipid A structures biosynthesized during its transit through the periplasm to the final localization in the outer surface of the outer membrane. Graphical
      PubDate: 2019-06-12
  • Integration of High-Resolution Mass Spectrometry with Cryogenic Ion
           Vibrational Spectroscopy
    • Abstract: We describe an instrumental configuration for the structural characterization of fragment ions generated by collisional dissociation of peptide ions in the typical MS2 scheme widely used for peptide sequencing. Structures are determined by comparing the vibrational band patterns displayed by cryogenically cooled ions with calculated spectra for candidate structural isomers. These spectra were obtained in a linear action mode by photodissociation of weakly bound D2 molecules. This is accomplished by interfacing a Thermo Fisher Scientific Orbitrap Velos Pro to a cryogenic, triple focusing time-of-flight photofragmentation mass spectrometer (the Yale TOF spectrometer). The interface involves replacement of the Orbitrap’s higher-energy collisional dissociation cell with a voltage-gated aperture that maintains the commercial instrument’s standard capabilities while enabling bidirectional transfer of ions between the high-resolution FT analyzer and external ion sources. The performance of this hybrid instrument is demonstrated by its application to the a1, y1 and z1 fragment ions generated by CID of a prototypical dipeptide precursor, protonated L-phenylalanyl-L-tyrosine (H+-Phe-Tyr-OH or FY-H+). The structure of the unusual z1 ion, nominally formed after NH3 is ejected from the protonated tyrosine (y1) product, is identified as the cyclopropane-based product is tentatively identified as a cyclopropane-based product.
      PubDate: 2019-06-10
  • Gas-Phase Synthesis and Reactivity of Ligated Group 10 Ions in the Formal
           +1 Oxidation State
    • Abstract: Electrospray ionization of the group 10 complexes [(phen)M(O2CCH3)2] (phen=1,10-phenanthroline, M = Ni, Pd, Pt) generates the cations [(phen)M(O2CCH3)]+, whose gas-phase chemistry was studied using multistage mass spectrometry experiments in an ion trap mass spectrometer with the combination of collision-induced dissociation (CID) and ion-molecule reactions (IMR). Decarboxylation of [(phen)M(O2CCH3)]+ under CID conditions generates the organometallic cations [(phen)M(CH3)]+, which undergo bond homolysis upon a further stage of CID to generate the cations [(phen)M]+· in which the metal center is formally in the +1 oxidation state. In the case of [(phen)Pt(CH3)]+, the major product ion [(phen)H]+ was formed via loss of the metal carbene Pt=CH2. DFT calculated energetics for the competition between bond homolysis and M=CH2 loss are consistent with their experimentally observed branching ratios of 2% and 98% respectively. The IMR of [(phen)M]+· with O2, N2, H2O, acetone, and allyl iodide were examined. Adduct formation occurs for O2, N2, H2O, and acetone. Upon CID, all adducts fragment to regenerate [(phen)M]+·, except for [(phen)Pt(OC(CH3)2)]+·, which loses a methyl radical to form [(phen)Pt(OCCH3)]+ which upon a further stage of CID regenerates [(phen)Pt(CH3)]+ via CO loss. This closes a formal catalytic cycle for the decomposition of acetone into CO and two methyl radicals with [(phen)Pt]+· as catalyst. In the IMR of [(phen)M]+· with allyl iodide, formation of [(phen)M(CH2CHCH2)]+ was observed for all three metals, whereas for M = Pt also [(phen)Pt(I)]+ and [(phen)Pt(I)2(CH2CHCH2)]+ were observed. Finally, DFT calculated reaction energetics for all IMR reaction channels are consistent with the experimental observations.
      PubDate: 2019-06-10
  • Spectroscopic Evidence for Lactam Formation in Terminal Ornithine b 2 +
           and b 3 + Fragment Ions
    • Abstract: Infrared multiple photon dissociation action spectroscopy was performed on the AlaOrn b2+ and AlaAlaOrn b3+ fragment ions from ornithine-containing tetrapeptides. Infrared spectra were obtained in the fingerprint region (1000–2000 cm−1) using the infrared free electron lasers at the Centre Laser Infrarouge d’Orsay (CLIO) facility in Orsay, France, and the free electron lasers for infrared experiments (FELIX) facility in Nijmegen, the Netherlands. A novel terminal ornithine lactam AO+ b2+ structure was synthesized for experimental comparison and spectroscopy confirms that the b2+ fragment ion from AOAA forms a lactam structure. Comparison of experimental spectra with scaled harmonic frequencies at the B3LYP/6-31+G(d,p) level of theory shows that AO+ b2+ forms a terminal lactam protonated either on the lactam carbonyl oxygen or the N-terminal nitrogen atom. Several low-lying conformers of these isomers are likely populated following IRMPD dissociation. Similarly, a comparison of the experimental IRMPD spectrum with calculated spectra shows that AAO+ b3+-ions also adopt a lactam structure, again with multiple different protonation sites, during fragmentation. This study provides spectroscopic confirmation for the lactam cyclization proposed for the “ornithine effect” and represents an alternative bn+ structure to the oxazolone and diketopiperazine/macrocycle structures most often formed.
      PubDate: 2019-06-10
  • Hydrogenated Gold Clusters from Helium Nanodroplets: Cluster Ionization
           and Affinities for Protons and Hydrogen Molecules
    • Abstract: We report the mass spectrometric detection of hydrogenated gold clusters ionized by electron transfer and proton transfer. The cations appear after the pickup of hydrogen molecules and gold atoms by helium nanodroplets (HNDs) near zero K and subsequent exposure to electron impact. We focus on the size distributions of the gold cluster cations and their hydrogen content, the electron energy dependence of the ion yield, patterns of hydrogenated gold cluster cation stability, and the presence of “magic” clusters. Ab initio molecular orbital calculations were performed to provide insight into ionization energies and proton affinities of gold clusters as well as into molecular hydrogen affinities of the ionized and protonated gold cluster cations.
      PubDate: 2019-06-05
  • Identification of Cross-linked Peptides Using Isotopomeric Cross-linkers
    • Abstract: Chemical cross-linking combined with mass spectrometry (CL-MS) is a powerful method for characterizing the architecture of protein assemblies and for mapping protein–protein interactions. Despite its proven utility, confident identification of cross-linked peptides remains a formidable challenge, especially when the peptides are derived from complex mixtures. MS cleavable cross-linkers are gaining importance for CL-MS as they permit reliable identification of cross-linked peptides by whole proteome database searching using MS/MS information. Here we introduce a novel class of MS cleavable cross-linkers called isotopomeric cross-linkers (ICLs), which allow for confident and efficient identification of cross-linked peptides by whole proteome database searching. ICLs are simple, symmetrical molecules that asymmetrically incorporate heavy and light stable isotopes into the two arms of the cross-linker. As a result of this property, ICLs automatically generate pairs of isotopomeric cross-linked peptides, which differ only by the positions of the heavy and light isotopes. Upon fragmentation during MS analysis, these isotopomeric cross-linked peptides generate unique isotopic doublet ions that correspond to the individual peptides in the cross-link. The doublet ion information is used to determine the masses of the two cross-linked peptides from the same MS2 spectrum that is also used for peptide spectrum matching (PSM) by sequence database searching. Here we present the rationale for and mechanism of cross-linked peptide identification by ICL-MS. We describe the synthesis of the ICL-1 reagent, the ICL-MS workflow, and the performance characteristics of ICL-MS for identifying cross-linked peptides derived from increasingly complex mixtures by whole proteome database searching.
      PubDate: 2019-06-05
  • Automatic Analyte-Ion Recognition and Background Removal for Ambient
           Mass-Spectrometric Data Based on Cross-Correlation
    • Abstract: Ambient mass spectrometry is a powerful approach for rapid, high-throughput, and direct sample analysis. Due to the open-air desorption and ionization processes, random fluctuations of ambient conditions can lead to large variances in mass-spectral signals over time. The mass-spectral data also can be further complicated due to multiple analytes present in the sample, background-ion signals stemming from the desorption/ionization source itself, and other laboratory-specific conditions (e.g., ambient laboratory air, nearby hardware). Thus, background removal and analyte-ion recognition can be quite difficult, particularly in non-targeted analyses. Here, we demonstrate the use of a cross-correlation-based approach to exploit chemical information encoded in the time domain to group/categorize mass-spectral peaks from a single analysis dataset. Ions that originate from ambient (or other) background species were readily flagged and removed from spectra; the result was a decrease in mass-spectral complexity by over 70% due to the removal of these background ions. Meanwhile, analyte ions were differentiated and categorized based on their time-domain profiles. With sufficient mass resolving-power and mass-spectral acquisition rate, isolated mass spectra containing ions from the same species in a sample could be extracted, leading to a reduction in mass-spectral complexity by more than 98% in some cases. The cross-correlation approach was tested with different ionization sources as well as reproducible and irreproducible sample introduction. Software built in-house enabled fully automated data processing, which can be performed within a few seconds. Ultimately, this approach provides an additional dimension of analyte separation in ambient mass-spectrometric analyses with information that is already recorded throughout the analysis.
      PubDate: 2019-06-03
  • Focus on Ion Mobility Spectrometry, Honoring Gert von Helden, Martin F.
           Jarrold, and David E. Clemmer, Recipients of the 2018 John B. Fenn Award
           for a Distinguished Contribution in Mass Spectrometry
    • PubDate: 2019-06-01
  • Effects of Individual Ion Energies on Charge Measurements in Fourier
           Transform Charge Detection Mass Spectrometry (FT-CDMS)
    • Abstract: A method to correct for the effect of ion energy on charge measurements of individual ions trapped and weighed with charge detection mass spectrometry (CDMS) is demonstrated. Ions with different energies induce different signal patterns inside an electrostatic ion trap. The sum of the amplitudes of the fundamental and second harmonic frequencies in the Fourier transform of the induced signal, which has been used to obtain the ion charge, depends on both ion energy and charge. The amplitudes of the fundamental frequencies of ions increase over time as ions lose energy by collisions with background gas and solvent loss from larger ions. Model ion signals are simulated with the same time-domain amplitude at different energies and frequencies and the resulting fundamental frequency amplitudes are used to normalize real ion signals for energy and frequency effects. The fundamental frequency amplitude decreases dramatically below 20 kHz and increases by ~ 17% from the highest energy to lowest energy that is stable with a given trap potential at all frequencies. Normalizing the fundamental frequency amplitude with the modeled amplitudes removes the systematic changes in the charge measurement of polyethylene glycol (PEG) and other ions and makes it possible to signal average the amplitude over long times, which reduces the charge uncertainty to 0.04% for a PEG ion for a 500-ms measurement. This method improves charge measurement accuracy and uncertainty, which are important for high-accuracy mass measurement with CDMS. Graphical abstract ᅟ
      PubDate: 2019-06-01
  • Evidence of Cis / Trans -Isomerization at Pro7/Pro16 in the Lasso Peptide
           Microcin J25
    • Abstract: Microcin J25 is a ribosomal synthesized and post-translationally modified peptide (RiPP) characterized by a mechanically interlocked topology called the lasso fold. This structure provides microcin J25 a potent antimicrobial activity resulting from internalization via the siderophore receptor FhuA and further inhibition of the RNA polymerase. In the present work, nuclear magnetic resonance (NMR) and trapped ion mobility spectrometry–mass spectrometry (TIMS-MS) were used to investigate the lasso structure of microcin J25. NMR experiments showed that the lasso peptide microcin J25 can adopt conformational states where Pro16 can be found in the cis- and trans-orientations. The high-resolution mobility analysis, aided by site-directed mutagenesis ([P7A], [P16A], and [P7A/P16A] variants), demonstrated that microcin J25 can adopt cis/cis-, cis/trans-, trans/cis-, and trans/trans-conformations at the Pro7 and Pro16 peptide bonds. It was also shown that interconversion between the conformers can occur as a function of the starting solvent conditions and ion heating (collision-induced activation, CIA) despite the lasso topology. Complementary to NMR findings, the cis-conformations at Pro7 were assigned using TIMS-MS. This study highlights the analytical power of TIMS-MS and site-directed mutagenesis for the study of biological systems with large micro-heterogeneity as a way to further increase our understanding of the receptor-binding dynamics and biological activity.
      PubDate: 2019-06-01
  • Substance P in the Gas Phase: Conformational Changes and Dissociations
           Induced by Collisional Activation in a Drift Tube
    • Abstract: The work presented below is related to our companion paper in this issue, entitled: Substance P in solution: trans-to-cis configurational changes of penultimate prolines initiate non-enzymatic peptide bond cleavages. Two-dimensional ion mobility spectrometry (IMS-IMS) and mass spectrometry techniques are used to investigate structural transitions for [M+3H]3+ ions of substance P (subP) upon collisional activation (CA) in the gas phase. In this approach, different conformations of ions having a specified mobility are selected after an initial IMS separation, collisionally activated to produce new conformers, and these product structures are separated again using a second IMS region. In this way, it is possible to follow folding and unfolding transitions of different conformations. The analysis shows evidence for five conformations. Unlike other systems, every transition is irreversible. Studies as a function of activation voltage are used to discern pathways of structural changes prior to reaching the energy required for dissociation. Thresholds associated with the onsets of transitions are calibrated to obtain estimates of the energetic barriers between different structures and semi-quantitative potential energy diagrams are presented. Overall, barriers associated with structural transitions of [subP+3H]3+ in the absence of solvent are on the order of ~ 40 kJ mol−1, substantially lower than the ~ 90 kJ mol−1 required for some similar structural transitions in solutions of ethanol. Comparisons of the transition energies in the gas phase with thermochemistry for similar transitions in solution provide clues about why reverse transitions are prohibited. Graphical
      PubDate: 2019-06-01
  • Structural Analysis of Polyurethane Monomers by Pyrolysis GC TOFMS via
           Dopant-Assisted Atmospheric Pressure Chemical Ionization
    • Abstract: Polyurethane is one of the most widely used copolymers and is formed by the cross-linking of isocyanates and polyols. Its physical properties have a strong dependence on the monomer structures, making it very important to characterize the monomers in polyurethane. In this study, we developed a method to analyze unknown polyurethane samples using pyrolysis gas chromatography time-of-flight mass spectrometry (Py-GC-TOFMS) with dopant-assisted atmospheric pressure chemical ionization (dAPCI). A set of standard polyurethane foams produced with several different monomers are analyzed by Py-GC-TOFMS. GC-dAPCI-TOFMS is a high-resolution, soft ionization method for GC-MS analysis that provides accurate mass information of GC separated molecules. The data obtained by this approach could effectively classify different monomers using principal component analysis (PCA), grouping polymers with the same monomers, and providing structural features significant to each monomer. Furthermore, characteristic compounds are identified using in-source collision-induced dissociation (CID) and CSI:FingerID analysis. In contrast, the same set of samples analyzed by Py-GC-electron ionization (EI)-MS could only partially separate some of the monomers. Graphical .
      PubDate: 2019-06-01
  • Thermodynamics and Reaction Mechanisms for Decomposition of a Simple
    • Abstract: We present a thorough characterization of fragmentations observed in threshold collision-induced dissociation (TCID) experiments of protonated glycylalanylglycine (H+GAG) with Xe using a guided ion beam tandem mass spectrometer. Kinetic energy dependent cross sections for nine ionic products were observed and analyzed to provide 0 K barriers for the six primary products: [b2]+, [y1 + 2H]+, [b3]+, CO loss, [y2 + 2H]+, and [a1]+; and three secondary products: [a2]+, [a3]+, and CH3CHNH2+, after accounting for multiple ion-molecule collisions, internal energy of reactant ions, unimolecular decay rates, competition between channels, and sequential dissociations. Relaxed potential energy surface scans performed at the B3LYP-GD3BJ/6-311+G(d,p) level of theory are used to identify transition states (TSs) and intermediates of the six primary and one secondary products (where the other two secondary products have mechanisms previously established). Geometry optimizations and single-point energy calculations were performed at several levels of theory. These theoretical energies are compared with experimental threshold energies and are found to give reasonably good agreement, with B3LYP-GD3BJ and M06-2X levels of theory performing better than other levels. The results obtained here are also compared with previous results for decomposition of H+GGG. The primary difference observed is a lowering of the threshold for the [b2]+ product ion and a concomitant suppression of the directly competing [y1 + 2H]+ product, the result of specific methylation of the [b2]+ product ion.
      PubDate: 2019-06-01
  • Real-Time Analysis and Signal Optimization for Charge Detection Mass
    • Abstract: Charge detection mass spectrometry (CDMS) is an important tool for measuring mass distributions for high mass samples and heterogeneous mixtures. In CDMS, single ions are trapped and their m/z and charge are measured simultaneously. As a single particle technique, the average signal must be optimized to maximize the number of single ion trapping events. If the average signal is too small, most of the trapping events will be empty, and if the average signal is too large, most of the trapping events will contain multiple ions. In recent embodiments, the time domain signal from the trapped ion is analyzed by fast Fourier transforms. The analysis time is much longer that the data collection time which precludes real-time optimization of the experimental conditions. In this paper, we describe the implementation of CDMS with real-time analysis. Processing the data in real time allows the average signal intensities to be dynamically optimized to maximize the number of single ion trapping events. Real-time analysis also allows the experimental settings to be optimized in a timely manner to target specific mass regimes to maximize the useful information content of the measurements. Graphical .
      PubDate: 2019-06-01
  • Rapid Solution-Phase Hydrogen/Deuterium Exchange for Metabolite Compound
    • Abstract: Rapid, solution-phase hydrogen/deuterium exchange (HDX) coupled with mass spectrometry (MS) is demonstrated as a means for distinguishing small-molecule metabolites. HDX is achieved using capillary vibrating sharp-edge spray ionization (cVSSI) to allow sufficient time for reagent mixing and exchange in micrometer-sized droplets. Different compounds are observed to incorporate deuterium with varying efficiencies resulting in unique isotopic patterns as revealed in the MS spectra. Using linear regression techniques, parameters representing contribution to exchange by different hydrogen types can be computed. In this proof-of-concept study, the exchange parameters are shown to be useful in the retrodiction of the amount of deuterium incorporated within different compounds. On average, the exchange parameters retrodict the exchange level with ~ 2.2-fold greater accuracy than treating all exchangeable hydrogens equally. The parameters can be used to produce hypothetical isotopic distributions that agree (± 16% RMSD) with experimental measurements. These initial studies are discussed in light of their potential value for identifying challenging metabolite species.
      PubDate: 2019-06-01
  • Selective Gas-Phase Mass Tagging via Ion/Molecule Reactions Combined with
           Single Analyzer Neutral Loss Scans to Probe Pharmaceutical Mixtures
    • Abstract: We have demonstrated the use of a simple single ion trap mass spectrometer to identify classes of compounds as well as individual components in complex mixtures. First, a neutral reagent was used to mass tag oxygen-containing analytes using a gas-phase ion/molecule reaction. Then, a neutral loss scan was used to indicate the carboxylic acids. The lack of unit mass selectivity in the neutral loss scan required subsequent product ion scans to confirm the presence and identity of the individual carboxylic acids. The neutral loss scan technique reduced the number of data-dependent MS/MS scans required to confirm identification of signals as protonated carboxylic acids. The method was demonstrated on neat mixtures of standard carboxylic acids as well as on solutions of relevant pharmaceutical tablets and may be generalizable to other ion/molecule reactions.
      PubDate: 2019-06-01
  • Evaluating Separation Selectivity and Collision Cross Section Measurement
           Reproducibility in Helium, Nitrogen, Argon, and Carbon Dioxide Drift Gases
           for Drift Tube Ion Mobility–Mass Spectrometry
    • Abstract: Previous ion mobility (IM) studies have demonstrated that varying the drift gas composition can be used to enhance chemical selectivity and resolution, yet there are few drift gas studies aimed at achieving quantitatively reproducible mobility measurements. Here, we critically evaluate the conditions necessary to achieve reproducible collision cross section (CCS) measurements in pure drift gases (helium, nitrogen, argon, and carbon dioxide) using a commercial uniform field drift tube instrument. Optimal experimental parameters are assessed based on the convergence of CCS measurements to reproducible values which are compared with literature values. A suite of calibration standards with diverse masses, biological classes, and charge states are examined to assess chemical selectivity and resolution achievable in each drift gas. Results indicate nitrogen and argon perform similarly and are sufficient for most applications where high resolving power and high peak capacity are desired. Carbon dioxide exhibits more selectivity for resolving structurally heterogeneous compounds, which may be preferable in specific analyte pair separations. Helium demonstrated modest separation capabilities but has utility for comparison to theoretical values and previously published work. In drift gases other than nitrogen, pressure differentials up to 230 mTorr between the drift tube and upstream chamber were optimal for improving correlation to literature values, while in nitrogen, the recommended pressure differential of 150 mTorr was found appropriate. We present recommended experimental parameters as well as gas-specific CCS measurements for structurally homogeneous sets of analytes which are suitable for use by other laboratories as standards for purposes of instrument calibration and overall assessment of IM separation performance.
      PubDate: 2019-06-01
  • Principles of Ion Selection, Alignment, and Focusing in Tandem Ion
           Mobility Implemented Using Structures for Lossless Ion Manipulations
    • Abstract: Tandem ion mobility (IM) enables the characterization of subpopulations of ions from larger ensembles, including differences that cannot be resolved in a single dimension of IM. Tandem IM consists of at least two IM regions that are each separated by an ion selection region. In many implementations of tandem IM, ions eluting from a dimension of separation are filtered and immediately transferred to the subsequent dimension of separation (selection-only experiments). We recently reported a mode of operation in which ions eluting from a dimension are trapped prior to the subsequent dimension (selection-trapping experiments), which was implemented on an instrument constructed using the structures for lossless ion manipulations (SLIM) architecture. Here, we use a combination of experiments and trajectory simulations to characterize aspects of the selection, trapping, and separation processes underlying these modes of operation. For example, the actual temporal profile of filtered ions can be very similar to the width of the waveforms used for selection, but depending on experimental parameters, can differ by up to ± 500 μs. Experiments and simulations indicate that ions in selection-trapping experiments can be spatially focused between dimensions, which removes the broadening that occurred during the preceding dimension. During focusing, individual ions are thermalized, which aligns and establishes common initial conditions for the subsequent dimension. Therefore, selection-trapping experiments appear to offer significant advantages relative to selection-only experiments, which we anticipate will become more pronounced in future experiments that make use of longer IM separations, additional dimensions of analysis, and the outcomes of this study. Graphical
      PubDate: 2019-06-01
  • Determination of Gas-Phase Ion Structures of Locally Polar Homopolymers
           Through High-Resolution Ion Mobility Spectrometry–Mass Spectrometry
    • Abstract: The strong synergy arising from coupling two orthogonal analytical techniques such as ion mobility and mass spectrometry can be used to separate complex mixtures and determine structural information of analytes in the gas phase. A tandem study is performed using two systems with different gases and pressures to ascertain gas-phase conformations of homopolymer ions. Aside from spherical and stretched configurations, intermediate configurations formed by a multiply charged globule and a “bead-on-a-string” appendix are confirmed for polyethylene-glycol (PEG), polycaprolactone (PCL), and polydimethylsiloxane (PDMS). These intermediate configurations are shown to be ubiquitous for all charge states and masses present. For each charge state, configurations evolve in two distinctive patterns: an inverse evolution which occurs as an elementary charge attached to the polymer leaves the larger globule and incorporates itself into the appendage, and a forward evolution which reduces the globule without relinquishing a charge while leaving the appendix relatively constant. Forward evolutions are confirmed to form self-similar family shapes that transcend charge states for all polymers. Identical structural changes occur at the same mass over charge regardless of the system, gas or pressure strongly suggesting that conformations are only contingent on number of charges and chain length, and start arranging once the ion is at least partially ejected from the droplet, supporting a charge extrusion mechanism. Configurational changes are smoother for PDMS which is attributed to the larger steric hindrance caused by protruding pendant groups. This study has implications in the study of the configurational space of more complex homopolymers and heteropolymers. Graphical
      PubDate: 2019-06-01
  • Increasing the Upper Mass/Charge Limit of a Quadrupole Ion Trap for
           Ion/Ion Reaction Product Analysis via Waveform Switching
    • Abstract: Quadrupole ion traps (QITs) are versatile platforms for performing experiments with gas-phase ions due to their abilities to store ions of both polarities and to conduct MSn experiments. The QIT is particularly useful as a reaction cell for ion/ion reactions. In the case of an ion/ion reaction experiment in a QIT, multiply charged reactant ions may initially be of relatively low m/z (e.g., m/z < 1000) whereas the product ions can be one or more orders of magnitude higher in m/z (e.g., m/z > 100,000). Several factors can limit the m/z range over which an ion/ion reaction experiment can be conducted. These include (1) the efficiency of the detector, (2) the m/z range over which oppositely charged ions can be mutually stored, and (3) the m/z range over which ions can be mass selectively ejected into an external detector. High-frequency waveforms provide larger m/z trapping ranges for mutual storage of oppositely charged ions whereas low-frequency waveforms provide better trapping for very high m/z product ions. Presented here is a method that switches from a high-frequency sine wave prior to and during an ion/ion reaction to a low-frequency square wave to eject low m/z reagent ions and improves confinement of the product ions before mass-selective ejection by scanning the frequency of the square wave. This approach addresses the third issue, which is the primary limiting factor with QITs operated at high RF (e.g., > 900 MHz). Graphical
      PubDate: 2019-06-01
School of Mathematical and Computer Sciences
Heriot-Watt University
Edinburgh, EH14 4AS, UK
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Fax: +00 44 (0)131 4513327
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