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Soft X-ray Spectroscopy as a Probe for Gas-Phase Protein Structure: Electron Impact Ionization from Within.

ABSTRACT: Preservation of protein conformation upon transfer into the gas phase is key for structure determination of free single molecules, for example using X-ray free-electron lasers. In the gas phase, the helicity of melittin decreases strongly as the protein's protonation state increases. We demonstrate the sensitivity of soft X-ray spectroscopy to the gas-phase structure of melittin cations ([melittin+qH]^q+ , q=2-4) in a cryogenic linear radiofrequency ion trap. With increasing helicity, we observe a decrease of the dominating carbon 1?s-?* transition in the amide C=O bonds for non-dissociative single ionization and an increase for non-dissociative double ionization. As the underlying mechanism we identify inelastic electron scattering. Using an independent atom model, we show that the more compact nature of the helical protein conformation substantially increases the probability for off-site intramolecular ionization by inelastic Auger electron scattering.

SUBMITTER: Bari S

PROVIDER: S-EPMC6001477 | biostudies-literature | 2018 May

REPOSITORIES: biostudies-literature

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Soft X-ray Spectroscopy as a Probe for Gas-Phase Protein Structure: Electron Impact Ionization from Within.

Bari Sadia S Egorov Dmitrii D Jansen Thomas L C TLC Boll Rebecca R Hoekstra Ronnie R Techert Simone S Zamudio-Bayer Vicente V Bülow Christine C Lindblad Rebecka R Leistner Georg G Ławicki Arkadiusz A Hirsch Konstantin K Miedema Piter S PS von Issendorff Bernd B Lau J Tobias JT Schlathölter Thomas T

Chemistry (Weinheim an der Bergstrasse, Germany) 20180503 30

Preservation of protein conformation upon transfer into the gas phase is key for structure determination of free single molecules, for example using X-ray free-electron lasers. In the gas phase, the helicity of melittin decreases strongly as the protein's protonation state increases. We demonstrate the sensitivity of soft X-ray spectroscopy to the gas-phase structure of melittin cations ([melittin+qH]<sup>q+</sup> , q=2-4) in a cryogenic linear radiofrequency ion trap. With increasing helicity, ...[more]

PMID: 29637635

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Project description:H-Abstraction reactions occurring during electron impact ionization processes in electron ionization mass spectrometry (EI-MS) are a long-standing and crucial topic in MS research. Yet, some critical relevant mechanisms are controversial and ambiguous, and information about the EI-induced H-abstraction reactions of halogenated organic compounds (HOCs) is completely in the dark. This study provides a systematic investigation of H-abstraction reactions of HOCs taking place in the EI source using 13C6-hexachlorobenzene (13C6-HCB) and 13C6-hexabromobenzene (13C6-HBB) as exemplary compounds by gas chromatography (GC)-high-resolution mass spectrometry (GC-HRMS). The H-abstraction efficiencies were evaluated with the MS signal intensity ratios of ions with H-abstraction relative to the corresponding original ions (without H-abstraction). Ion source temperatures, EI energies, and numbers of heavy isotope atoms (37Cl or 81Br) of isotopologues were investigated in terms of their effects on the H-abstraction efficiencies. The H-abstraction efficiencies of individual isotopologues generally decreased from the first to the last isotopologues of respective ions, and those of individual ions were different from each other, with the highest values of 0.017 and 0.444 for 13C6-HCB and 13C6-HBB, respectively. The overall H-abstraction efficiencies involving all measured ions of 13C6-HCB and 13C6-HBB were 0.004 and 0.128, respectively. With increasing ion source temperatures, the H-abstraction efficiencies first increased to a summit and then began to linearly decrease. EI energies and emission currents could impact the H-abstraction efficiencies but showed no certain tendency. The H-abstraction reactions were inferred to belong to ion-molecule reactions, and the siloxanes bleeding from the GC column might be a hydrogen source. Some strategies were proposed for eliminating or alleviating the interference triggered by the H-abstraction reactions in EI-MS in identification of halogenated organic pollutants (HOPs). Our findings provide a better understanding of the EI-induced H-abstraction reactions of HOCs and may benefit the identification of HOPs in environmental analysis, especially for novel HOPs.

Dataset Information

Soft X-ray Spectroscopy as a Probe for Gas-Phase Protein Structure: Electron Impact Ionization from Within.

Publications

Soft X-ray Spectroscopy as a Probe for Gas-Phase Protein Structure: Electron Impact Ionization from Within.

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