Structural studies of metal ligand complexes by ion mobility-mass spectrometry

Collision cross sections (CCS) have been measured for three salen ligands, and their complexes with copper and zinc using travelling-wave ion mobility-mass spectrometry (TWIMS) and drift tube ion mobility-mass spectrometry (DTIMS), allowing a comparative size evaluation of the ligands and complexes. CCS measurements using TWIMS were determined using peptide and TAAH calibration standards. TWIMS measurements gave significantly larger CCS than DTIMS in helium, by 9 % for TAAH standards and 3 % for peptide standards, indicating that the choice of calibration standards is important in ensuring the accuracy of TWIMS-derived CCS measurements. Repeatability data for TWIMS was obtained for inter- and intra-day studies with mean RSDs of 1. 1 % and 0. 7 %, respectively. The CCS data obtained from IM-MS measurements are compared to CCS values obtained via the projection approximation, the exact hard spheres method and the trajectory method from X-ray coordinates and modelled structures using density functional theory (DFT) based methods. © 2013 Springer-Verlag Berlin Heidelberg

Recommendations for reporting ion mobility mass spectrometry measurements

© 2019 The Authors. Mass Spectrometry Reviews Published by Wiley Periodicals, Inc. Here we present a guide to ion mobility mass spectrometry experiments, which covers both linear and nonlinear methods: what is measured, how the measurements are done, and how to report the results, including the uncertainties of mobility and collision cross section values. The guide aims to clarify some possibly confusing concepts, and the reporting recommendations should help researchers, authors and reviewers to contribute comprehensive reports, so that the ion mobility data can be reused more confidently. Starting from the concept of the definition of the measurand, we emphasize that (i) mobility values (K0) depend intrinsically on ion structure, the nature of the bath gas, temperature, and E/N; (ii) ion mobility does not measure molecular surfaces directly, but collision cross section (CCS) values are derived from mobility values using a physical model; (iii) methods relying on calibration are empirical (and thus may provide method-dependent results) only if the gas nature, temperature or E/N cannot match those of the primary method. Our analysis highlights the urgency of a community effort toward establishing primary standards and reference materials for ion mobility, and provides recommendations to do so. © 2019 The Authors. Mass Spectrometry Reviews Published by Wiley Periodicals, Inc

Initial protein unfolding events revealed by 213 nm UVPD coupled to IM-MS

In this work we couple UVPD with activated ion mobility mass spectrometry to measure how three model proteins start to unfold. Ubiquitin, cytochrome c and myoglobin ions produced via nESI from salty solutions are subjected to UV irradiation pre-mobility separation, experiments are conducted with a range of source conditions which alter the conformation of the precursor ion as shown by the drift time profiles. For all three proteins the compact structures result in less fragmentation than more extended structures which emerge following progressive in-source activation. Cleavage sites are found to differ between conformational ensembles, for example, for the dominant charge state of cytochrome c [M+7H]⁷⁺, cleavage at Phe10, Thr19 and Val20 was only observed in activating conditions while cleavage at Ala43 is dramatically enhanced. Mapping the photo-cleaved fragments onto crystallographic structures provides insight into the local structural changes that occur as protein unfolding progresses, which is coupled to global restructuring observed in the drift time profiles

Mobilising Ion Mobility Mass Spectrometry in a Synthetic Biology Analytics Workflow

<p>Chromatography based mass spectrometry approaches (xC-MS) are commonly used in untargeted metabolomics, providing retention time, m/z values and metabolite specific-fragments all of which are used to identify and validate an unknown analyte. Ion mobility-mass spectrometry (IM-MS) is emerging as an enhancement to classic xC-MS strategies, by offering additional separation as well as collision cross section (CCS) determination. In order to apply such an approach to a synthetic biology workflow, verified data from metabolite standards is necessary. In this work we present experimental ^DTCCS_N2 values for a range of metabolites in positive and negative ionisation modes using drift time-ion mobility-mass spectrometry (DT-IM-MS) with nitrogen as the buffer gas. Creating a useful database containing ^DTCCS_N2 measurements for application in metabolite identification relies on a robust technique that acquires measurements of high reproducibility. We report that 86% of the metabolites measured in replicate have a relative standard deviation lower than 0.2 %. Examples of metabolites with near identical mass are demonstrated to be separated by ion mobility with over 4% difference in ^DTCCS_N2 values. We conclude that the integration of ion mobility into current LC-MS workflows can aid in small molecule identification for both targeted and untargeted metabolite screening which is commonly performed in synthetic biology.</p

Confusion matrix for reduced-feature PLS-DA model projected on to COVID-19 negative participants.

Confusion matrix for reduced-feature PLS-DA model projected on to COVID-19 negative participants.</p

Distinctive features between COVID-19 positive and negative.

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Summary of clinical characteristics by participant cohort.

Summary of clinical characteristics by participant cohort.</p

Operating conditions of the mass spectrometer used in this research.

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Principal component analysis for 44 participants and 324 features, high severity / low severity, LC-MS analysis in positive mode.

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Workflow summary—Recruitment, processing and results, produced with Biorender.com.

Workflow summary—Recruitment, processing and results, produced with Biorender.com.</p