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Zhijie Wu, Yutong Jin, Bifan Chen, Morgan K. Gugger, Chance L. Wilkinson-Johnson, Timothy N. Tiambeng, Song Jin,
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2561-2570; https://doi.org/10.1007/s13361-019-02341-0

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Roshan Javanshad, Tara L. Maser, Elahe Honarvar,
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2571-2575; https://doi.org/10.1007/s13361-019-02345-w

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Alexander Haack, Jeff Crouse, Femke-Jutta Schlüter, ,
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2711-2725; https://doi.org/10.1007/s13361-019-02340-1

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Dahang Yu, Zhe Wang, Kellye A. Cupp-Sutton, Xiaowen Liu,
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2502-2513; https://doi.org/10.1007/s13361-019-02315-2

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Matthew V. Holt, Tao Wang,
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2548-2560; https://doi.org/10.1007/s13361-019-02350-z

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Alfonso Espada, Ruben Haro, Jesus Castañon, Cristina Sayago, Francisco Perez-Cozar, Leticia Cano, Pablo Redero, Manuel Molina-Martin, Howard Broughton, Ryan E. Stites, et al.
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2580-2583; https://doi.org/10.1007/s13361-019-02331-2

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Ke Sherry Li, Elizabeth T. Schaper Bergman, Brett R. Beno, , Ekaterina Deyanova, Guodong Chen,
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2795-2804; https://doi.org/10.1007/s13361-019-02316-1

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Kiran Iyer, Brett M. Marsh, Grace O. Capek, Robert L. Schrader, ,
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2584-2593; https://doi.org/10.1007/s13361-019-02307-2

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Xinhao Yang, Feixian Luo, Junqi Li, Deyang Chen, Ye E., Weili Lin,
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2762-2770; https://doi.org/10.1007/s13361-019-02347-8

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Andrea Carrà, Veronica Macaluso, Peter W. Villalta, ,
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2771-2784; https://doi.org/10.1007/s13361-019-02348-7

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Daniel Y. Botamanenko,
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2741-2749; https://doi.org/10.1007/s13361-019-02343-y

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Jiana Duan, Lauren Pepi,
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2692-2703; https://doi.org/10.1007/s13361-019-02338-9

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Journal of the American Society for Mass Spectrometry, Volume 30, pp 2678-2691; https://doi.org/10.1007/s13361-019-02337-w

Abstract:
Imidazole (IMI) is a basic building block of many biologically important compounds. Thus, its electron ionization properties are of major interest and essential for the comparison with other molecular targets containing its elemental structure. 2-Nitroimidazole (2NI) contains the imidazole ring together with nitrogen dioxide bound to the C2 position, making it a radiosensitizing compound in hypoxic tumors. In the present study, we investigated electron ionization of IMI and 2NI and determined the mass spectra, the ionization energies, and appearance energies of the most abundant fragment cations. The experiments were complemented by quantum chemical calculations on the thermodynamic thresholds and potential energy surfaces, with particular attention to the calculated transition states for the most important dissociation reactions. In the case of IMI, substantially lower threshold values (up to ~ 1.5 eV) were obtained in the present work compared to the only available previous electron ionization study. Closer agreement was found with recent photon ionization values, albeit the general trend of slightly higher values for the case of electron ionization. The only exception for imidazole was found in the molecular cation at m/z 40 which is tentatively assigned to the quasi-linear HCCNH+/ HCNCH+. Electron ionization of 2NI leads to analogous fragment cations as in imidazole, yet different dissociation pathways must be operative due to the presence of the NO2 group. Regarding the potential radiosensitization properties of 2NI, electron ionization is characterized by dominant parent cation formation and release of the neutral NO radical.
Mickaël Chevalier, Emma Ricart, Emeline Hanozin, , Philippe Jacques, Nicolas Smargiasso, Edwin De Pauw, Frédérique Lisacek, Valérie Leclère,
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2608-2616; https://doi.org/10.1007/s13361-019-02314-3

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Lauren Pintabona, Alina Astefanei, ,
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2655-2669; https://doi.org/10.1007/s13361-019-02335-y

Abstract:
When considering incident investigations and security checks focused on energetic materials, there is an ongoing need for rapid, on-scene chemical identification. Currently applied methods are not capable of meeting all requirements, and hence, portable mass spectrometry is an interesting alternative although many instrumental challenges still exist. To be able to analyze explosives with mass spectrometry outside the traditional laboratory, suitable ambient ionization methods need to be developed. Ideally such methods are also easily implemented in the field requiring limited to no power sources, gas supplies, flow controllers, and heating devices. For this reason, the potential of SAWN (surface acoustic wave nebulization) for the ambient ionization and subsequent mass spectrometric (MS) analysis of organic explosives was investigated in this study. Excellent sensitivity was observed for nitrate-based organic explosives when operating the MS in negative mode. No dominant adduct peaks were observed for the peroxides TATP and HMTD with SAWN-MS in positive mode. The MS spectra indicate extensive fragmentation of the peroxide explosives even under the mild ionization conditions provided by SAWN. The potential of SAWN-MS was demonstrated with the correct identification of nitrate-based organic explosives in pre- and post-explosion case samples in only a fraction of the time and effort required for the regular laboratory analysis. Results show that SAWN-MS can convincingly identify intact organic energetic compounds and mixtures but that sensitivity is not always sufficient to detect traces of explosives in post-explosion residues.
, Paul Martini, Arne Schiller, Paul Scheier
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2632-2636; https://doi.org/10.1007/s13361-019-02329-w

Abstract:
We present a study of cationic and protonated clusters of neon and krypton. Recent studies using argon have shown that protonated rare gas clusters can have very different magic sizes than pure, cationic clusters. Here, we find that neon behaves similarly to argon, but that the cationic krypton is more similar to its protonated counterparts than the lighter rare gases are, sharing many of the same magic numbers.
Jeremy Manheim, Katherine Wehde, Wan Tang Jeff Zhang, Petr Vozka, Mark Romanczyk, Gozdem Kilaz,
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2670-2677; https://doi.org/10.1007/s13361-019-02336-x

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Xu Zhao, Jing Chen, Weiying Zhang, Chengdui Yang, , Sichun Zhang,
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2646-2654; https://doi.org/10.1007/s13361-019-02334-z

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Maria A. van Agthoven, David P. A. Kilgour, Alice M. Lynch, Mark P. Barrow, Tomos E. Morgan, Christopher A. Wootton, Lionel Chiron, ,
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2594-2607; https://doi.org/10.1007/s13361-019-02308-1

Abstract:
Two-dimensional mass spectrometry (2D MS) is a data-independent tandem mass spectrometry technique in which precursor and fragment ion species can be correlated without the need for prior ion isolation. The behavior of phase in 2D Fourier transform mass spectrometry is investigated with respect to the calculation of phase-corrected absorption-mode 2D mass spectra. 2D MS datasets have a phase that is defined differently in each dimension. In both dimensions, the phase behavior of precursor and fragment ions is found to be different. The dependence of the phase for both precursor and fragment ion signals on various parameters (e.g., modulation frequency, shape of the fragmentation zone) is discussed. Experimental data confirms the theoretical calculations of the phase in each dimension. Understanding the phase relationships in a 2D mass spectrum is beneficial to the development of possible algorithms for phase correction, which may improve both the signal-to-noise ratio and the resolving power of peaks in 2D mass spectra.
Nicole A. Schneck, Vera B. Ivleva, Erwin Rosales-Zavala, Xiangchun Wang, Deepika Gollapudi, Jonathan W. Cooper,
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2576-2579; https://doi.org/10.1007/s13361-019-02318-z

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Neville J. A. Coughlan, , Michael J. Lecours, ,
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2222-2227; https://doi.org/10.1007/s13361-019-02332-1

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Patrick M. Wehrli, Wojciech Michno, Kaj Blennow, Henrik Zetterberg,
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2278-2288; https://doi.org/10.1007/s13361-019-02327-y

Abstract:
Imaging mass spectrometry (IMS) is a promising new chemical imaging modality that generates a large body of complex imaging data, which in turn can be approached using multivariate analysis approaches for image analysis and segmentation. Processing IMS raw data is critically important for proper data interpretation and has significant effects on the outcome of data analysis, in particular statistical modeling. Commonly, data processing methods are chosen based on rational motivations rather than comparative metrics, though no quantitative measures to assess and compare processing options have been suggested. We here present a data processing and analysis pipeline for IMS data interrogation, processing and ROI annotation, segmentation, and validation. This workflow includes (1) objective evaluation of processing methods for IMS datasets based on multivariate analysis using PCA. This was then followed by (2) ROI annotation and classification through region-based active contours (AC) segmentation based on the PCA component scores matrix. This provided class information for subsequent (3) OPLS-DA modeling to evaluate IMS data processing based on the quality metrics of their respective multivariate models and for robust quantification of ROI-specific signal localization. This workflow provides an unbiased strategy for sensitive annotation of anatomical regions of interest combined with quantitative comparison of processing procedures for multivariate analysis allowing robust ROI annotation and quantification of the associated molecular histology.
Hiroshi Ushijima, Rena Maekawa, Eri Igarashi,
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2335-2346; https://doi.org/10.1007/s13361-019-02304-5

Abstract:
CpG methylation of DNA is an epigenetic marker that is highly related to the regulation of transcription initiation. For analysis of CpG methylation in genomic DNA sequences, bisulfite-induced modification in combination with polymerase chain reaction (PCR) is usually utilized, but it cannot be straightforwardly applied to methylated short- and middle-sized DNAs, such as < 500 base pairs (bp), which are often utilized in structural biology studies. In the present study, we applied nano-electrospray ionization mass spectrometry (nano-ESI-MS) for the characterization of methylated DNA with < 400 bp prepared in vitro. First, double-stranded DNA oligomers were methylated with recombinant M.SssI DNA methylase, which has been reported to modify completely and exclusively CpG sites in the sequence. The fragments generated by the digestion with methylation-insensitive restriction nuclease were then analyzed to identify the methylation levels by nano-ESI-MS, without liquid chromatography (LC) separation. By methylation-insensitive nuclease digestion, we divided the DNA strands into several fragments, and nano-ESI-MS enabled the accurate analysis of methylation levels in the DNA fragments with a relatively small amount of DNA sample prepared under optimized conditions. Furthermore, it was revealed that M.SssI methylase hardly modifies the CpG sites closely positioned at the ends of linear DNA. The present method is similar to the strategy for post-translational modification analysis of proteins and is promising for the rapid and definitive characterization of methylated DNA that may be used in structural biology studies.
, Cédric Delvaux, Jean R. N. Haler, , Gauthier Eppe, Edwin De Pauw, Johann Far
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2238-2249; https://doi.org/10.1007/s13361-019-02321-4

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Stephan Warnke, Ahmed Ben Faleh, Valeriu Scutelnic,
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2204-2211; https://doi.org/10.1007/s13361-019-02333-0

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Jared O. Kafader, Steven C. Beu, Bryan P. Early, Rafael D. Melani, Kenneth R. Durbin, Vlad Zabrouskov, Alexander A. Makarov, Joshua T. Maze, Deven L. Shinholt, Ping F. Yip, et al.
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2200-2203; https://doi.org/10.1007/s13361-019-02309-0

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Syed G. T. Kazimi, , Christopher C. Mulligan, C. Frank Shaw, Fozia Iram, Ashley R. Stelmack, Ian S. Campbell
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2289-2296; https://doi.org/10.1007/s13361-019-02319-y

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, Thomas Auth
Journal of the American Society for Mass Spectrometry, Volume 30, pp 1857-1866; https://doi.org/10.1007/s13361-019-02312-5

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Ri Wu, , Wei-Jing Wu, Ze Wang, Y.-L. Elaine Wong, Y.-L. Winnie Hung, H.-T. Wong, Minli Yang, Feng Zhang,
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2212-2221; https://doi.org/10.1007/s13361-019-02317-0

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David Olivenza-León, Chris A. Mayhew,
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2259-2266; https://doi.org/10.1007/s13361-019-02325-0

Abstract:
This paper presents an investigation of proton and charge transfer reactions to 2-, 3- and 4-nitroanilines (C6H6N2O2) involving the reagent ions H3O+·(H2O)n (n = 0, 1 and 2) and O2+, respectively, as a function of reduced electric field (60–240 Td), using Selective Reagent Ion–Time-of-Flight–Mass Spectrometry (SRI–ToF–MS). To aid in the interpretation of the H3O+·(H2O)n experimental data, the proton affinities and gas-phase basicities for the three nitroaniline isomers have been determined using density functional theory. These calculations show that proton transfer from both the H3O+ and H3O+·H2O reagent ions to the nitroanilines will be exoergic and hence efficient, with the reactions proceeding at the collisional rate. For proton transfer from H3O+ to the NO2 sites, the exoergicities are 171 kJ mol−1 (1.8 eV), 147 kJ mol−1 (1.5 eV) and 194 kJ mol−1 (2.0 eV) for 2-, 3- and 4-nitroanilines, respectively. Electron transfer from all three of the nitroanilines is also significantly exothermic by approximately 4 eV. Although a substantial transfer of energy occurs during the ion/molecule reactions, the processes are found to predominantly proceed via non-dissociative pathways over a large reduced electric field range. Only at relatively high reduced electric fields (> 180 Td) is dissociative proton and charge transfer observed. Differences in fragment product ions and their intensities provide a means to distinguish the isomers, with proton transfer distinguishing 2-nitroaniline (2–NA) from 3- and 4-NA, and charge transfer distinguishing 4-NA from 2- and 3-NA, thereby providing a means to enhance selectivity using SRI–ToF–MS.
Remilekun O. Lawal, Fabrizio Donnarumma,
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2196-2199; https://doi.org/10.1007/s13361-019-02313-4

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, Shadab Ahmad, Swetaketu Majumder, , Ben Orsburn
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2408-2418; https://doi.org/10.1007/s13361-019-02306-3

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Emmanuel Colson, Corentin Decroo, Dale Cooper-Shepherd, , Céline Henoumont, Sophie Laurent, , , Martin Palmer, Jan Claereboudt, et al.
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2228-2237; https://doi.org/10.1007/s13361-019-02310-7

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C. C. He, L. A. Hamlow, , Y.-W. Nei, L. Fan, C. P. McNary, , V. Steinmetz, B. Schindler, I. Compagnon, et al.
Journal of the American Society for Mass Spectrometry, Volume 30, pp 2318-2334; https://doi.org/10.1007/s13361-019-02300-9

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