Crown ethers as shift reagents in peptide epimer differentiation \u2013conclusions from examination of ac-(H)FRW-NH2 petide sequences

Ion mobility spectrometry (IMS) is a gas-phase separation technique based on ion mobility differences in an electric field. It is largely used for the detection of specific ions such as small molecule explosives. IMS detection system includes the use of e. g. a Faraday cupor mass spectrometry (MS). The presence of interfering ion signals in standalone IMS may lead to the detection of false positives or negatives due to e. g. lacking resolving power. In this case, selective mobility shifts obtained using shift reagents (SR), i. e. ligands complexing a specific target, can bring help. The effectiveness of an SR strategy relies on the SR-target ion selectivity. The crucial step lies in the SR design. The aim of this paper is to present an efficient interplay of experimental ion mobility mass spectrometry (IMMS) and predictive computational chemistry using various levels of computational efforts for rationally designing target-specific SR. Mass spectrometry is used to evaluate the efficiency of the SR selectivity with identification and semi-quantification of free and complexed ions. Minimal computational efforts allow the design of the SR, predicting the SR-target ion relative stabilities, and predicting the ion mobility shifts. We demonstrate our approach using crown ethers and β-cyclodextrin to selectively shift interfering perchlorate, amino acids and diaminonaphthalene isomers. We also release the software ParsIMoS for the straightforward use of ion mobility calculator IMoS.

A high resolution ion mobility spectrometer was interfaced to a Synapt G2 high definition mass spectrometer (HDMS) to produce IMMS-IMMS analysis. The hybrid instrument contained an electrospray ionization source, two ion gates, an ambient pressure linear ion mobility drift tube, a quadrupole mass filter, a traveling wave ion mobility spectrometer (TWIMS), and a time-of-flight mass spectrometer. The dual gate drift tube ion mobility spectrometer (DTIMS) could be used to acquire traditional IMS spectra but also could selectively transfer specific mobility selected precursor ions to the Synapt G2 HDMS for mass filtration (quadrupole). The mobility and mass selected ions could then be introduced into a collision cell for fragmentation followed by mobility separation of the fragment ions with the traveling wave ion mobility spectrometer. These mobility separated fragment ions are finally mass analyzed using a time-of-flight mass spectrometer. This results in an IMMS-IMMS analysis and provides a method to evaluate the isomeric heterogeneity of precursor ions by both DTIMS and TWIMS to acquire a mobility-selected and mass-filtered fragmentation pattern and to additionally obtain traveling wave ion mobility spectra of the corresponding product ions. This new IMMS(2) instrument enables the structural diversity of carbohydrates to be studied in greater detail. The physical separation of isomeric oligosaccharide mixtures was achieved by both DTIMS and TWIMS, with DTIMS demonstrating higher resolving power (70-80) than TWIMS (30-40). Mobility selected MS/MS spectra were obtained, and TWIMS evaluation of product ions showed that isomeric forms of fragment ions existed for identical m/z values.

The research papers in this issue of the International Journal for Ion Mobility Spectrometry are the concluding articles of a two-part special issue on Travelling Wave Ion Mobility. The first issue, published in March (Volume 16, Issue 1, March 2013), covered a wide range of research areas: ‘Resolving the microcosmos of complex samples: UPLC/travelling wave ion mobility separation high resolution mass spectrometry for the analysis of in vivo drug metabolism studies’ by Blech and Laux; ‘The effects of cation adduction upon the conformation of three-helix bundle protein domains’ by Sokratous et al.; ‘Monitoring oligomer formation from self-aggregating amylin peptides using ESI-IMS-MS’ by Young et al.; ‘Traveling-wave ion mobility-mass spectrometry reveals additional mechanistic details in the stabilization of protein complex ions through tuned salt additives’ by Han and Ruotolo; 'Coupling electrospray corona discharge, charge reduction and ion mobility mass spectrometry: From peptides to large macromolecular protein complexes' by Campuzano and Schnier; and 'Structural studies of metal ligand complexes by ion mobility-mass spectrometry' by Wright et al. The papers in this issue extend upon the range of studies presented in the first issue and together they illustrate the broad utility and applicability of (travelling wave) ion mobility—mass spectrometry. Since the launch of the first travelling wave ion mobility system (SYNAPT) some 7 years ago, the interest in ion mobility coupled with mass spectrometry has grown tremendously and shows no sign of abating. We continue to push the boundaries of ion mobility instrumentation design and, together with our customers and collaborators, work to extend the applications of this technology. I am indebted to the small cross-section of our customers/collaborators who have taken the time to contribute to this special issue on Travelling Wave Ion Mobility and offer my sincere thanks.

The research papers in this issue of the International Journal for Ion Mobility Spectrometry are the concluding articles of a two-part special issue on Travelling Wave Ion Mobility. The first issue, published in March (Volume 16, Issue 1, March 2013), covered a wide range of research areas: ‘Resolving the microcosmos of complex samples: UPLC/travelling wave ion mobility separation high resolution mass spectrometry for the analysis of in vivo drug metabolism studies’ by Blech and Laux; ‘The effects of cation adduction upon the conformation of three-helix bundle protein domains’ by Sokratous et al.; ‘Monitoring oligomer formation from self-aggregating amylin peptides using ESI-IMS-MS’ by Young et al.; ‘Traveling-wave ion mobility-mass spectrometry reveals additional mechanistic details in the stabilization of protein complex ions through tuned salt additives’ by Han and Ruotolo; 'Coupling electrospray corona discharge, charge reduction and ion mobility mass spectrometry: From peptides to large macromolecular protein complexes' by Campuzano and Schnier; and 'Structural studies of metal ligand complexes by ion mobility-mass spectrometry' by Wright et al. The papers in this issue extend upon the range of studies presented in the first issue and together they illustrate the broad utility and applicability of (travelling wave) ion mobility—mass spectrometry. Since the launch of the first travelling wave ion mobility system (SYNAPT) some 7 years ago, the interest in ion mobility coupled with mass spectrometry has grown tremendously and shows no sign of abating. We continue to push the boundaries of ion mobility instrumentation design and, together with our customers and collaborators, work to extend the applications of this technology. I am indebted to the small cross-section of our customers/collaborators who have taken the time to contribute to this special issue on Travelling Wave Ion Mobility and offer my sincere thanks.

Traveling wave ion mobility (TWIM) mass spectrometry (MS) is a powerful method for the structural and conformational analysis of proteins and peptides, enabling the differentiation of isomeric peptides (or proteins) that have the same sequence but are modified at different residues. In this study, the TWIM-MS technique was used to separate isomeric AuI metallopeptide ions that were formed by ZnII displacement from the parent zinc fingers (ZFs). The synthetic gold finger peptides were derived from the C-terminus of the HIV nucleocapsid p7 protein (NCp7-F2) and finger 3 of the Sp1 transcription factor (Sp1-F3). TWIM-MS enabled the acquisition of distinct product ion spectra for each isomer, clearly indicating the binding sites for the major conformers in the presence of multiple coordination possibilities. Collision cross-section measurements showed that the aurated peptide has a slightly more compact structure than the parent zinc compound NCp7-F2, which showed only one conformation.

We present the design and implementation of a home-built point-to-plane corona discharge probe, which rapidly and efficiently charge reduces biological ions generated by electrospray ionization (ESI). The molecules analysed ranged from small peptides such as Glu-fibrinopeptide B (1.5 kDa), small proteins such as myoglobin (16.9 kDa), polymers such as polyethylene glycol (PEG 10 k) which all showed intense singly charged ions; to large native multiprotein complexes such as GroEL (802 kDa) which show a broad range of charge-reduced species. The corona discharge probe operates at atmospheric pressure and was directly interfaced with a standard-ESI or nanoflow-ESI source of quadrupole ion mobility time-of-flight mass spectrometer. The corona discharge probe is completely modular and could potentially be mounted to any commercial or research grade mass spectrometer with an ESI source. The level of charge reduction is precisely controlled by the applied voltage and/or probe gas flow rate and when in operation, results in approximately a 50 % reduction in total ion current. We also present the combination of corona discharge and travelling wave ion mobility and assign helium collision cross-section values (ΩHe) to the charge reduced species of the native protein complex pyruvate kinase. It would appear that the ΩHe of the +20 charge state for pyruvate kinase is approximately 20 % smaller than the +35 charge state. Finally, we discuss the potential benefits and concerns of utilising charge reduced protein species as a means of extending the travelling wave collision cross-section calibration range over that which is already published.

离子淌度质谱(IM-MS)是一种将离子淌度分离与质谱分析相结合的新型分析技术。IM-MS的主要优势不仅是在质谱检测前提供了基于气相离子形状、大小、电荷数等因素的多一维分离,而且能够提供碰撞截面积、漂移时间等质谱信息进而辅助化合物鉴定。近年来,随着IM-MS技术的不断发展,该技术在中药化学成分分析中受到越来越多的关注。首先,IM-MS已成功应用于改善中药复杂成分尤其是同分异构体或等量异位素等成分的分离;其次,IM-MS可通过多重碎裂模式辅助高质量中药小分子质谱信息的获取;此外,IM-MS提供的高维质谱数据信息还可促进中药复杂体系多成分的整合分析。该文在对IM-MS分类和基本原理进行概述的基础上,从分离能力及分离策略、多重碎裂模式、多维质谱数据处理策略3个方面,重点综述了IM-MS在中药化学成分分析中的应用,以期为IM-MS在中药化学成分研究提供参考。

Modern mass spectrometry methods provide a huge benefit to saponin structural characterization, especially when combined with collision-induced dissociation experiments to obtain a partial description of the saponin (ion) structure. However, the complete description of the structures of these ubiquitous secondary metabolites remain challenging, especially since isomeric saponins presenting small differences are often present in a single extract. As a typical example, the horse chestnut triterpene glycosides, the so-called escins, comprise isomeric saponins containing subtle differences such as cis-trans ethylenic configuration (stereoisomers) of a side chain or distinct positions of an acetyl group (regioisomers) on the aglycone. In the present paper, the coupling of liquid chromatography and ion mobility mass spectrometry has been used to distinguish regioisomeric and stereoisomeric saponins. Ion mobility arrival time distributions (ATDs) were recorded for the stereoisomeric and regioisomeric saponin ions demonstrating that isomeric saponins can be partially separated using ion mobility on a commercially available traveling wave ion mobility (TWIMS) mass spectrometer. Small differences in the ATD can only be monitored when the isomeric saponins are separated with liquid chromatography prior to the IM-MS analysis. However, gas phase separation between stereoisomeric and regioisomeric saponin ions can be successfully realized, without any LC separation, on a cyclic ion mobility-enabled quadrupole time-of-flight (Q-cIM-oaToF) mass spectrometer. The main outcome of the present paper is that the structural analysis of regioisomeric and stereoisomeric natural compounds that represents a real challenge can take huge advantages of ion mobility experiments but only if increased ion mobility resolution is attainable.

Monosaccharide structural isomers including sixteen methyl-D-glycopyranosides and four methyl-N-acetylhexosamines were subjected to ion mobility measurements by electrospray ion mobility mass spectrometry. Two ion mobility-MS systems were employed: atmospheric pressure drift tube ion mobility time-of-flight mass spectrometry and a Synapt G2 HDMS system which incorporates a low pressure traveling wave ion mobility separator. All the compounds were investigated as [M + Na](+) ions in the positive mode. A majority of the monosaccharide structural isomers exhibited different mobility drift times in either system, depending on differences in their anomeric and stereochemical configurations. In general, drift time patterns (relative drift times of isomers) matched between the two instruments. Higher resolving power was observed using the atmospheric pressure drift tube. Collision cross section values of monosaccharide structural isomers were directly calculated from the atmospheric pressure ion mobility experiments, and a collision cross section calibration curve was made for the traveling wave ion mobility instrument. Overall, it was demonstrated that ion mobility-mass spectrometry using either drift tube or traveling wave ion mobility is a valuable technique for resolving subtle variations in stereochemistry among the sodium adducts of monosaccharide methyl glycosides.

BackgroundThere is an increasing usage of ion mobility-mass spectrometry (IMMS) in proteomics. IMMS combines the features of ion mobility spectrometry (IMS) and mass spectrometry (MS). It separates and detects peptide ions on a millisecond time-scale. IMS separates peptide ions based on drift time that is determined by the collision cross-section of each peptide ion in a given experiment condition. A peptide ion's collision cross-section is related to the ion size and shape resulted from the peptide amino acid sequence and their modifications. This inherent relation between the drift time of peptide ion and peptide sequence indicates that the drift time of peptide ions can be used to infer peptide sequence and therefore, for peptide identification.ResultsThis paper describes an artificial neural networks (ANNs) regression model for the prediction of peptide ion drift time in IMMS. Each peptide in this work was represented using three descriptors (i.e., molecular weight, sequence length and a two-dimensional sequence index). An ANN predictor consisting of four input nodes, three hidden nodes and one output node was constructed for peptide ion drift time prediction. For the model training and testing, a 10-fold cross-validation strategy was employed for three datasets each containing different charge states. Dataset one contains 212 singly-charged peptide ions, dataset two has 306 doubly-charged peptide ions, and dataset three has 77 triply-charged peptide ions. Our proposed method achieved 94.4%, 93.6% and 74.2% prediction accuracy for singly-, doubly- and triply-charged peptide ions, respectively.ConclusionsAn ANN-based method has been developed for predicting the drift time of peptide ions in IMMS. The results achieved here demonstrate the effectiveness and efficiency of the prediction model. This work can enhance the confidence of protein identification by combining with current database search approaches for protein identification.

Isomeric oligosaccharides gamma-cyclodextrin (gamma-CD), glucosyl-betaCD (Glc1-betaCD) and maltosyl-alphaCD (Glc2-alphaCD) were analyzed by traveling-wave ion mobility (twIM) mass spectrometry (MS). Their formation of multicharged multimers differed from each other. The ion mobility-mass spectrometry was useful in the self-assembling and complex formation analyses of CD isomers. The drift times of the isomers and their product ions with the same mass were almost the same in collision-induced dissociation (CID) MS/MS. In contrast, the ion mobility peak widths were sensitive to structural differences of the isomeric product ions. The twIM peak width (ms-micros) of the product ions [M-Glc(n) + H]+ (n = 0-6) of gamma-CD correlated linearly with their masses (Da); the large and/or long chain product ions had wider peak widths, which were much wider than those from the general diffusion effect. This was a novel and useful 'trend line' to discriminate between the three isomers. Plots of [M-Glc(2-6) + H]+ of Glc1-betaCD and [M-Glc(3-6) + H]+ of Glc2-alphaCD product ions' plots were on the same trend line as gamma-CD. The plots of [M-Glc1 + H]+ of Glc1-betaCD and [M-Glc(1, 2) + H]+ of Glc2-alphaCD strayed from the gamma-CD line; their peak widths were narrower than those of gamma-CD. These results indicated that product ions from the chemical species of Glc1-beta CD and Glc2-alphaCD retained their CD structure. Analyses of the IM peak widths enable us to elucidate the structures of the product ions.

Metabolic profiling of human blood by high-resolution ion mobility mass spectrometry (IM-MS)

Ion mobility mass spectrometry (IM-MS) can be used to differentiate and identify isobaric ions. To improve IM-MS resolution, the second generation of traveling wave ion mobility (TWIM) technology was launched. There were reports showing ions were heated up by TWIM. With higher ion energy, it could alter the conformation of larger ions or MS/MS experiments. To monitor the energy exchange relating to the TWIM process, the combined use of thermometer ions with unique molecular structure and theoretical calculations to determine the effective temperature of ions had been explored. In this report, the use of a simple experimental approach to estimate the variation on the ion energy that result from changing a TWIM parameter setting is demonstrated. The approach aims to achieve the same percentage of ion dissociation in a collision cell, which is part of the original instrument and located at the exit of TWIM cell. Similar to the traditional MS/MS experiments, the same level of ion dissociation could be achieved by adjusting the electrical potential that was applied to the collision cell. The higher the ion energy after the TWIM separation, the lower the electrical potential was required to achieve the same level of ion dissociation. Together with the information on the number of electrical charge in the selected ion, the difference in the required electrical potentials could be converted into electron volt of ion energy that resulted from changing the TWIM parameter setting. The results showed ion energy could be changed 1–9 eV when the parameter of TWIM was adjusted.

Structures of flexible supramolecular cations (1,4-cyclohexanediammonium 2+)(crown ethers) 2 in [Ni(dmit) 2] − salts

ADVERTISEMENT RETURN TO ISSUEPREVReviewNEXTIon Mobility-Mass Spectrometry: Time-Dispersive InstrumentationJody C. May and John A. McLean*View Author Information Department of Chemistry, Center for Innovative Technology, Vanderbilt Institute for Chemical Biology, Vanderbilt Institute for Integrative Biosystems Research and Education , Vanderbilt University, Nashville, Tennessee 37235, United States*E-mail: [email protected]Cite this: Anal. Chem. 2015, 87, 3, 1422–1436Publication Date (Web):December 19, 2014Publication History Published online9 January 2015Published inissue 3 February 2015https://doi.org/10.1021/ac504720mCopyright © 2014 American Chemical SocietyRIGHTS & PERMISSIONSACS AuthorChoiceArticle Views13748Altmetric-Citations286LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (4 MB) Get e-AlertsSUBJECTS:Collisions,Ions,Mass spectrometers,Optimization,Power Get e-Alerts