International Journal of Mass Spectrometry最新文献

{"title":"Structural analysis of echinocandins via high-performance liquid chromatography-quadrupole/time-of-flight-tandem mass spectrometry","authors":"Hanzhi Zhang ,&nbsp;Xiakun Wang ,&nbsp;Bin Xu ,&nbsp;Zhenhua Tian ,&nbsp;Yu Luo ,&nbsp;Zhijun Tang ,&nbsp;Wen Liu","doi":"10.1016/j.ijms.2025.117475","DOIUrl":"10.1016/j.ijms.2025.117475","url":null,"abstract":"<div><div>Herein, the structures of echinocandins were analyzed by high-performance liquid chromatography-quadrupole/time-of-flight-tandem mass spectrometry (HPLC-Q/TOF-MS/MS). The echinocandin components were separated by using a Diamonsil Plus C18 column (5 μm, 4.6 mm × 250 mm), with 0.1 % formic acid in water as mobile phase A and 0.1 % formic acid in acetonitrile as mobile phase B under gradient elution. A systematic strategy for the structural characterization of echinocandin B, which is the main component of echicandins, is presented based on the accurate molecular mass and diagnostic ions obtained from both adduct ions [M+H]⁺ and [M+Na]⁺ as precursor ions. In the three fragmentation pathways obtained from the precursor ion of [M+H]⁺, echinocandins and its fragment ions produced continuous dehydrated ions ([M-<em>n</em>H₂O + H]⁺, <em>n</em> = 1, 2, 3, 4). The <em>N</em>-terminal fatty acyl (FA) connecting to the ornithine derivative transferred to the amino group of the proline derivative during fragmentation. Different characteristic ions, depending on the number of hydroxyls (0, 1, 2) on the ornithine derivative of different echinocandin analog. Moreover, the threonine residues underwent the neutral consecutive loss of acetaldehyde from the [M+Na]⁺ precursor ion. The [M+H]⁺ and [M+Na]⁺ echinocandin precursor ions respectively lost 1-(4-hydroxyphenyl)ethane-1,2-diol and 2-hydroxy-2-(4-hydroxyphenyl)acetaldehyde from the homotyrosine residues to generate different fragmentation ions. Thirteen echinocandin analogs were identified, including echinocandin C, echinocandin D, and echinocandin B variants with different FA and amino acid compositions.</div></div>","PeriodicalId":338,"journal":{"name":"International Journal of Mass Spectrometry","volume":"515 ","pages":"Article 117475"},"PeriodicalIF":1.6,"publicationDate":"2025-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144243010","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Chirality effects on the intrinsic acidity of isomeric tripeptides containing a D/L-Cysteine on the N-terminus: CAA and dCAA","authors":"Shiyuan Wang,&nbsp;Zachary Buen,&nbsp;Kimberlyann R. Harvey,&nbsp;Yuntao Zhang,&nbsp;Jianhua Ren","doi":"10.1016/j.ijms.2025.117472","DOIUrl":"10.1016/j.ijms.2025.117472","url":null,"abstract":"<div><div>Chirality effects on the intrinsic gas-phase acidity of oligopeptides have been studied using a pair of stereoisomeric tripeptides consisting of a D/L-cysteine (C) and two residues of alanine (A): CAA and ^dCAA, where the C-terminus is amidated. Mass spectrometry measurements through bracketing via collision-induced dissociation clearly show that CAA is a stronger gas-phase acid than ^dCAA. Quantitative values of the acidity were determined using the extended Cooks kinetic method. The resulting deprotonation enthalpy (<em>Δ</em>_acid<em>H</em>) for CAA is 326.2 kcal/mol (1364.7 kJ/mol) and for ^dCAA it is 326.8 kcal/mol (1367.6 kJ/mol). The corresponding gas-phase acidity (<em>Δ</em>_acid<em>G</em>) for CAA is 321.3 kcal/mol (1344.2 kJ/mol) and for ^dCAA it is 322.0 kcal/mol (1347.3 kJ/mol). Changing the N-terminal cysteine from the L-form to the D-form reduces the gas-phase acidity by about 0.6 kcal/mol (2.5 kJ/mol). Extensive conformational searches followed by quantum chemical calculations at the ωB97X-D/6-311+G(d,p) level of theory yielded a set of lowest energy conformations for each peptide species. Theoretical gas-phase acidities calculated using the Boltzmann averaged conformational contributions are in good agreement with the experimental data. The shift in the acidity is likely due to the conformational effect induced by D-cysteine, which increases the stability of the neutral ^dCAA, and hence reduces its acidity. A chirality change on a single amino acid can have a noticeable effect on the biochemical properties of peptides and proteins.</div></div>","PeriodicalId":338,"journal":{"name":"International Journal of Mass Spectrometry","volume":"514 ","pages":"Article 117472"},"PeriodicalIF":1.6,"publicationDate":"2025-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144139461","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Miniature APCI ion source using AC corona discharge in a PFA tube: its application to the analysis of low-volatility compounds coupled with heat pulse desorption mass spectrometry (HPD/MS)","authors":"Stephanie Rankin-Turner ,&nbsp;Satoshi Ninomiya ,&nbsp;Haruo Shimada ,&nbsp;Kazumasa Kinoshita ,&nbsp;Kenzo Hiraoka","doi":"10.1016/j.ijms.2025.117461","DOIUrl":"10.1016/j.ijms.2025.117461","url":null,"abstract":"<div><div>DC corona discharge has long been used as the APCI ion source. In 2013, Habib et al. first proposed AC corona discharge as an APCI ion source and found that it is superior to DC as an ambient ion source [1]. In this study, an ion source using AC corona enclosed in a PFA (perfluoroalkoxy) tube (i.d.: 2 mm) was developed as a miniature APCI ion source coupled with heat pulse desorption mass spectrometry (HPD-MS) and used for the desorption of low-volatility compounds. Diverse materials were introduced, demonstrating the potential to apply the miniature ion source to gas-phase analytes, liquid samples, and solid materials in their native state. The modified technique was utilized in the analysis of a range of samples, including solid and liquid pharmaceuticals, food products, plant material, insects, and human biofluids, highlighting the wide applicability of the miniature APCI ion source across diverse sample types and fields of study.</div></div>","PeriodicalId":338,"journal":{"name":"International Journal of Mass Spectrometry","volume":"514 ","pages":"Article 117461"},"PeriodicalIF":1.6,"publicationDate":"2025-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143922788","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Impact of glucagon oxidation on fibril formation","authors":"Aleksandra Antevska ,&nbsp;Gaoyuan Lu ,&nbsp;Emmanuel Nkyaagye ,&nbsp;Sarah S. Hirschbeck ,&nbsp;Connor C. Long ,&nbsp;Lingjun Li ,&nbsp;Thanh D. Do","doi":"10.1016/j.ijms.2025.117468","DOIUrl":"10.1016/j.ijms.2025.117468","url":null,"abstract":"<div><div>Glucagon structural dynamics is crucial for its function and pathology, yet its oligomerization and fibrillization mechanisms remain unclear. The early assembly of glucagon into fibrils is a critical process that can be perturbed by oxidation at key residues. In this study, we systematically tracked the oligomer formation of native glucagon up to the decamer level, revealing that glucagon undergoes oxidation at tryptophan and methionine—residues essential to its steric zipper structure. Our findings also indicate that oxidation exerts a dual effect on glucagon fibrillation. At low concentrations, oxidation partially unfolds glucagon's α-helix, facilitating hetero-oligomer formation between oxidized and native peptides, which promotes further oligomerization and unfolding. However, at high concentrations, oxidized glucagon fails to self-assemble into fibrils and appears more susceptible to degradation. Chromatographic analysis differentiates native and oxidized glucagon, highlighting increased polarity and multiple elution peaks indicative of diverse oxidative states, while mass spectrometry confirms site-specific modifications that influence structural transitions. These results emphasize the fine balance between oxidation and self-assembly, with implications for glucagon's therapeutic stability. An understanding of oxidation-induced aggregation dynamics is essential for developing stable glucagon formulations, underscoring the importance of controlling oxidative conditions to preserve their functionality and efficacy.</div></div>","PeriodicalId":338,"journal":{"name":"International Journal of Mass Spectrometry","volume":"514 ","pages":"Article 117468"},"PeriodicalIF":1.6,"publicationDate":"2025-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144090129","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"An in situ analysis of the components of HTS vapor using a home-made high-temperature time-of-flight mass spectrometer","authors":"Zejie Fei,&nbsp;Min Ge,&nbsp;Yuan Qian,&nbsp;Hongtao Liu,&nbsp;Yuanyuan Tang","doi":"10.1016/j.ijms.2025.117471","DOIUrl":"10.1016/j.ijms.2025.117471","url":null,"abstract":"<div><div>The aim of this study was to propose the decomposition mechanism of heat transfer salt (HTS or Hitec salt) using a high-temperature furnace coupled with a time-of-flight mass spectrometer (TOF-MS). The decomposition process was systematically investigated in a vacuum environment at temperatures of 45 °C, 80 °C, 150 °C, 200 °C, 220 °C and 280 °C. The thermal decomposition of HTS initiated at and above 200 °C, which was slightly higher than its melting point of 142 °C. The main products resulting from the thermochemical reactions of nitrate/nitrite were NO and N₂ respectively, followed by N₂O. These findings revealed an unconventional reaction pathways for HTS decompositions as it contradicted the common assumption that O₂ or NO₂ would be present during this process. These new evidences further support the existence of intermediate species, such as superoxide and peroxide ions, in the molten salts during the initial thermal-chemical reaction process involving nitrite/nitrate salts.</div></div>","PeriodicalId":338,"journal":{"name":"International Journal of Mass Spectrometry","volume":"514 ","pages":"Article 117471"},"PeriodicalIF":1.6,"publicationDate":"2025-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144106834","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Determining β-monosaccharide head group composition with high-resolution cyclic ion mobility separations coupled to tandem mass spectrometry as a first step for unknown cerebroside analysis","authors":"Cameron N. Naylor,&nbsp;Gabe Nagy","doi":"10.1016/j.ijms.2025.117459","DOIUrl":"10.1016/j.ijms.2025.117459","url":null,"abstract":"<div><div>Cerebrosides, a class of biologically important lipids, are comprised of a monosaccharide head group along with their ceramide tail. However, their accurate characterization is challenging because of the isomerism in both the tail, from potential double bond positioning, or in the head from monosaccharide composition and α/β anomericity. In this work, we focused on tackling the identification of the β-monosaccharide head group, as either glucose or galactose, in various cerebroside isomers as well as demonstrating how our methodology could be applied to unknowns found in a porcine extract. To achieve this, we performed collision-induced dissociation prior to cyclic ion mobility separations to generate monosaccharide fragment ions from the starting cerebroside precursor ions. With this pre-cIMS CID approach, we observed that the cIMS separations of the fragment ions were diagnostic of the β-monosaccharide head group composition (i.e., glucose versus galactose), regardless of the ceramide tail length. From there, we demonstrated an example of how this methodology could also be applied to cerebrosides found in a porcine extract and a framework for how this approach could be added to existing workflows in developing collision cross section databases. Overall, we envision that our developed pre-cIMS CID-based approach will be a complementary and orthogonal tool to existing ones in glycolipidomics workflows.</div></div>","PeriodicalId":338,"journal":{"name":"International Journal of Mass Spectrometry","volume":"514 ","pages":"Article 117459"},"PeriodicalIF":1.6,"publicationDate":"2025-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143887651","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Emissions of volatile organic compounds from COVID-19 response hospitals using mobile proton transfer reaction mass spectrometry observations in Wuhan in 2020","authors":"Qu Liang ,&nbsp;Xun Bao ,&nbsp;Chenghua Qin ,&nbsp;Qiangling Zhang ,&nbsp;Xue Zou ,&nbsp;Wei Xu ,&nbsp;Chaoqun Huang ,&nbsp;Chengyin Shen ,&nbsp;Yannan Chu","doi":"10.1016/j.ijms.2025.117460","DOIUrl":"10.1016/j.ijms.2025.117460","url":null,"abstract":"<div><div>To curb the rapid spread of the COVID-19, Wuhan was the first in the world to implement strict lockdown measures on January 23, 2020, and rapidly established several large hospitals. The extensive disinfection operations and daily activities within these hospitals led to the release of significant amounts of volatile organic compounds (VOCs). However, the composition and concentration characteristics of VOCs around these hospitals remain unclear. This study employed a self-developed mobile proton transfer reaction mass spectrometry (M-PTR-MS) system to conduct high spatiotemporal resolution mobile monitoring of VOCs in these hospitals in Wuhan from February 29 to March 15, 2020. The study compared the temporal and spatial variations in VOC across Wuhan, focusing on the frequency and concentration of VOC increases downwind of temporary hospital (Leishenshan Hospital), designated hospitals (Wuhan Xiehe Hospital, Wuhan Jinyintan Hospital), and shelter hospitals (Wuhan Keting Shelter Hospital, Hongshan Stadium Shelter Hospital). The results indicated that during the 14 days of effective mobile monitoring, the average concentration of total VOC (TVOC) in the first seven days was 13.39 % higher than in the latter seven days. Spatially, the average concentration of TVOC in the industrial areas north of the Yangtze River was 8.89 % higher than those in the non-industrial areas south of the river. Leishenshan Hospital exhibited the most diverse VOC composition and sources, with VOCs primarily originating from the fermentation and direct incineration of medical, waste within the hospital grounds and disinfectants. Downwind of the designated hospitals, VOCs related to industrial-source, disinfectants and waste were detected. Ethanol was detected downwind of all these hospitals. Waste generated by hospitals was a significant source of VOCs downwind of both temporary and designated hospitals. This study provides valuable technology for the research on VOC characteristics, disinfection efficacy evaluation, and environmental impact analysis during public health emergencies.</div></div>","PeriodicalId":338,"journal":{"name":"International Journal of Mass Spectrometry","volume":"514 ","pages":"Article 117460"},"PeriodicalIF":1.6,"publicationDate":"2025-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143912565","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effect of the Tyr5 and His6 substituent groups on the zinc affinities and conformational structures of the acetyl-His1-Cys2-Gly3-Pro4-X5-X6-Cys7 heptapeptides","authors":"Richmond A. Adomako,&nbsp;Michael B. Owusu,&nbsp;Rebekah Oberdick,&nbsp;Kwabena N. Senyah,&nbsp;Perfect Asare,&nbsp;Laurence A. Angel","doi":"10.1016/j.ijms.2025.117458","DOIUrl":"10.1016/j.ijms.2025.117458","url":null,"abstract":"<div><div>In this study, we investigate the influence of the Tyr₅ and His₆ substituent groups on the zinc-binding affinities and conformational properties of a series of acetylated heptapeptides, acetyl-His₁-Cys₂-Gly₃-Pro₄-X₅-X₆-Cys₇ focusing on the impacts where X₅-X₆ are either Tyr₅-Gly₆, Tyr₅-His₆, Gly₅-Gly₆, or Gly₅-His₆. Utilizing traveling-wave ion mobility-mass spectrometry and molecular modeling techniques we analyze the zinc binding interactions and peptide coordination behavior. The zinc binding peptides (ZBPs) relative zinc affinities were measured across pH 5 to pH 10 by monitoring the solution-phase formation of the [ZBP+Zn(II)]⁻ complex by utilizing native MS in negative ion mode to preserve the solution-phase binding of Zn(II) to the peptides. Furthermore, their relative gas-phase Zn(II) affinities were measured using competitive threshold collision-induced dissociation (TCID) of the [ZBP+Zn(II)+NTA]⁻ complex, by modeling the two competing dissociation channels: [ZBP+Zn(II)]⁻ + NTA or [Zn(II)+NTA]⁻ + ZBP, where NTA is nitrilotriacetic acid. Our examinations also tested whether there was an effect of the formation of the [ZBP+Zn(II)+NTA]⁻ complexes from solutions at different pHs, before they are electrosprayed into the gas-phase for the TCID analyses. Both solution- and gas-phase measurements predicted the heptapeptide with the Gly₅-His₆ residues had the greatest zinc affinity and that the presence of Tyr₅ and His₆ altered the zinc affinity and induced distinct conformational changes due to changes in the coordination of the zinc. This research enhances our understanding of zinc-peptide interactions, with implications for the design of peptide-based metalloproteins, which may guide the design of novel ZBPs for therapeutic, biotechnological or environmental remediation applications.</div></div>","PeriodicalId":338,"journal":{"name":"International Journal of Mass Spectrometry","volume":"513 ","pages":"Article 117458"},"PeriodicalIF":1.6,"publicationDate":"2025-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143882961","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Approaches with different reaction gases for the determination of iron in rare earth samples based on on-mass mode by inductively coupled plasma tandem mass spectrometer","authors":"Zhe Fang ,&nbsp;Haizhou Wang ,&nbsp;Lei Wang ,&nbsp;Kai Li","doi":"10.1016/j.ijms.2025.117456","DOIUrl":"10.1016/j.ijms.2025.117456","url":null,"abstract":"<div><div>The determination of iron using ICP-MS-MS is complicated due to the polyatomic spectral interferences, notably the ⁴⁰Ar¹⁶O⁺ on the abundant ⁵⁶Fe isotope. In this research, the utilization of three gases—helium, hydrogen, and methane—to accurately quantify iron was proposed using the on-mass mode by inductively coupled plasma tandem mass spectrometer. The conditions of the collision/reaction cell were optimized, particularly the gas flow rate and the hexapole bias voltage, for iron analysis. Different mechanisms, including collision and reactions like charge transfer reactions, hydrogen atom transfer reactions, and proton transfer reactions, were explored. In terms of sensitivity and background equivalent concentration (BEC), the hydrogen mode exhibited the highest sensitivity and the lowest BEC. The methane mode yields a comparable BEC to that of the hydrogen mode with a threefold reduction in sensitivity. The limit of quantification (LOQ) under the hydrogen reaction mode was as low as 0.028 μg/g.The analysis results of the national standard substance GBW07159 were in excellent agreement with the certified values, and the relative standard deviation (RSD) for n = 11 was less than 5 % in the three modes. The measured values and spiked recoveries for rare earth oxides were essentially consistent between the hydrogen and methane modes. Following validation, the hydrogen and methane reaction modes have been shown to accurately analyze iron in rare earth and rare earth oxides with high accuracy and stability, surpassing the helium mode in terms of collision mechanism.</div></div>","PeriodicalId":338,"journal":{"name":"International Journal of Mass Spectrometry","volume":"513 ","pages":"Article 117456"},"PeriodicalIF":1.6,"publicationDate":"2025-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143839724","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Residue-specific pathways in peptide fragmentation: The role of aromatic side chain in a3 ion formation from b3 ion","authors":"A. Emin Atik ,&nbsp;Sila Karaca ,&nbsp;Talat Yalcin","doi":"10.1016/j.ijms.2025.117457","DOIUrl":"10.1016/j.ijms.2025.117457","url":null,"abstract":"<div><div>Peptide fragmentation chemistry is essential for the sequence elucidation of proteins through tandem mass spectrometry (MS/MS). In this study, we examine the gas-phase fragmentation of <em>b</em>₃ ions from model tripeptides under low-energy CID conditions, focusing on the pathway leading to the stable formation of <em>a</em>₃ ions from <em>b</em>₃ ions. The study utilized C-terminal amidated model tripeptides, including YGG-NH₂, GYG-NH₂, and GGX-NH₂, where X represents D, E, H, Q, C, S, F, and Y. Our results reveal that only tripeptides with phenylalanine (F) and tyrosine (Y) as the third residue yield <em>a</em>₃ ions upon <em>b</em>₃ ion fragmentation under the applied experimental conditions, suggesting a unique stabilizing role of aromatic side chains in facilitating this pathway. Our theoretical studies indicate that the <em>a</em>₃ ions from GGF-NH₂ and GGY-NH₂ preferentially adopt an energetically favored linear imine-protonated isomer, which is lower in energy by 3.29 kcal/mol and 4.17 kcal/mol, respectively, compared to their 7-membered ring isomers protonated at the ring imine. The latter structure has been previously assigned for the GGG sequence as a predominant structure, supported by IR spectroscopy and DFT calculations <em>(JACS, 2010, 132, 14,766–14779)</em>. We proposed a plausible fragmentation mechanism for the <em>a</em>₃ ions based on the linear imine-protonated structure. These findings provide insights into residue-specific fragmentation mechanisms and enhance our understanding of peptide ion dissociation, particularly in small peptides.</div></div>","PeriodicalId":338,"journal":{"name":"International Journal of Mass Spectrometry","volume":"513 ","pages":"Article 117457"},"PeriodicalIF":1.6,"publicationDate":"2025-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143828450","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}