Journal of the American Society for Mass Spectrometry最新文献

{"title":"Library Enabling Annotation of Botanical Natural Products (LEAFBot): An Open-Access Library of Mass Spectrometry Fragmentation Spectra for Plant Metabolites.","authors":"Victoria M Anderson, Madhusha M Ranaweera, Alan K Jarmusch, Ashley E Shay, Daniel A Todd, Nadja B Cech, Joshua J Kellogg","doi":"10.1021/jasms.5c00038","DOIUrl":"https://doi.org/10.1021/jasms.5c00038","url":null,"abstract":"<p><p>Many existing mass spectral libraries focus on human or microbially derived molecules. Few plant-specific MS² databases exist, making annotation of botanical samples difficult. To fill this gap in mass spectrometry data availability, the Library Enabling Annotation of Botanical Natural Products (LEAFBot) was constructed. Using a flow injection mass spectrometry method that allowed for rapid throughput data collection, the MS² spectra of >300 pure botanical secondary metabolites were experimentally measured and complied into a single library housed in the Global Natural Products Social Molecular Networking (GNPS) spectral database. Of these compounds, over 20% were not present in the existing GNPS database, and 11% were not present in any of three main mass spectral databases (GNPS, Metlin, and MassBank). Additionally, LEAFBot contains a wider range of adducts compared to other plant-based mass spectral libraries, enabling more effective annotation of unknown features. The LEAFBot database represents a new resource to the mass spectrometry and metabolomics community seeking to characterize plant-based samples. The possibility of searching against a taxonomically specific library decreases the likelihood of false positives in database searches, and the ease of adding new spectra, following procedures outlined herein, will enable community-lead expansion of the database.</p>","PeriodicalId":672,"journal":{"name":"Journal of the American Society for Mass Spectrometry","volume":"36 5","pages":"926-929"},"PeriodicalIF":3.1,"publicationDate":"2025-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143959452","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Factorial-Design-Based Optimization of a Commercial MALDI-2 timsTOF Mass Spectrometer for Lipid Analysis.","authors":"Seth W Croslow, Chen H Sirois, Jonathan V Sweedler","doi":"10.1021/jasms.4c00424","DOIUrl":"10.1021/jasms.4c00424","url":null,"abstract":"<p><p>Matrix-assisted laser desorption/ionization mass spectrometry with laser postionization (MALDI-2 MS) has become an important technique for the analysis of a wide range of biomolecules. It has traditionally been limited to custom lab-built setups until the recent introduction of a commercial timsTOF fleX MALDI-2 system. A comprehensive optimization of the timsTOF fleX system for lipid analysis was performed using a factorial design of experiments (DOE). By examining 13 instrumental parameters across three full factorial DOEs, we performed over 1500 individual runs to assess the impact and cross interactions of these parameters on the lipid signal intensity. We found optimal values for both ion transmission and MALDI-2 parameters to maximize the signals within the lipid region. These results show that laser shot frequency, collision RF, and pre pulse storage were essential for enhancing lipid ion transmission, resulting in a nearly 5-fold increase in signal intensity compared to default parameters. For MALDI-2 optimization, positive and negative modes showed similar optimized values, with TIMS In pressure and laser power being crucial. Overall, optimization of ion optics and MALDI-2 resulted in signal enhancements of nearly 2 orders of magnitude for certain lipid species.</p>","PeriodicalId":672,"journal":{"name":"Journal of the American Society for Mass Spectrometry","volume":" ","pages":"942-951"},"PeriodicalIF":3.1,"publicationDate":"2025-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12058408/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143741744","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Dual Apodization Maximizes Charge Resolution and Frequency Precision in Charge Detection Mass Spectrometry.","authors":"Raj A Parikh, Martin F Jarrold","doi":"10.1021/jasms.5c00049","DOIUrl":"https://doi.org/10.1021/jasms.5c00049","url":null,"abstract":"<p><p>Charge detection mass spectrometry (CD-MS) is a single-particle technique in which the masses of individual ions are determined from simultaneous measurements of their <i>m</i>/<i>z</i> ratio and charge. Ions are trapped in an electrostatic linear ion trap and oscillate back and forth through a detection cylinder coupled to a low noise charge sensitive amplifier. The resulting signal is analyzed using short-time Fourier transforms (STFTs) to determine the <i>m</i>/<i>z</i> ratio and charge. The <i>m</i>/<i>z</i> ratio is determined from the oscillation frequency, and the charge is obtained from the magnitude of the fundamental. Here we compare the methods used to analyze time domain data for single ion measurements including STORI plots. We conclude that the original STFT approach remains the best method for the analysis of CD-MS data. However, there are many ways of implementing the STFT approach. We compare the options with the goal of maximizing precision of the charge and <i>m</i>/<i>z</i> determinations while simultaneously maximizing the number of ions that are detected. A variety of apodization methods are compared, and the effects of scalloping loss, equivalent noise bandwidth, computation time, window length, and step size are evaluated. Maximizing the precision of the charge and <i>m</i>/<i>z</i> determinations places conflicting constraints on the window length, and we conclude that a dual apodization strategy, with different window lengths, provides the most robust approach to analyzing results for the broad range of different samples that can be measured by CD-MS.</p>","PeriodicalId":672,"journal":{"name":"Journal of the American Society for Mass Spectrometry","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2025-05-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143956761","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Differentiating Isomeric Urea Derivatives by Cyclic Ion Mobility-Mass Spectrometry, Host-Guest Chemistry, and Tandem Mass Spectrometry.","authors":"Sudam S Mane, Cole D Warner, David V Dearden, Kenneth W Lee","doi":"10.1021/jasms.5c00062","DOIUrl":"https://doi.org/10.1021/jasms.5c00062","url":null,"abstract":"<p><p>Alkyl pyridyl ureas are crucial precursors in medicinal and agricultural chemistry. Their isomeric forms, which are distinguished by the position of pyridyl nitrogen relative to the urea functionality, pose challenges in mass spectrometric identification due to their isobaric molecular ions. This study presents orthogonal methods to differentiate 1-phenyl-3-(2-pyridyl) urea (ortho), 1-phenyl-3-(3-pyridyl) urea (meta), and 1-phenyl-3-(4-pyridyl) urea (para). Cyclic ion mobility separation of protonated molecules and their complexes with β-cyclodextrin was employed. While the protonated ortho and para isomers were baseline resolved after six passes, the meta and para isomers were not separated after 40 passes. After complexation with β-cyclodextrin, we observed two peaks for each isomer. The peak that arrived first (peak A) is a doubly protonated dimer of the host-guest complex, while the later arriving peak (peak B) corresponds to the singly protonated host-guest complex. Peak B for the β-cyclodextrin complex of the meta and para compounds was resolved after three passes. Thus, the differentiation of meta and para isomers was achieved after complexation with β-cyclodextrin. Overall, the two methods (ion mobility of protonated molecules and ion mobility of host-guest complexes) led to orthogonal results. Collision-induced dissociation of protonated molecules revealed identical fragment ions at <i>m</i>/<i>z</i> 95 and 121, but their relative intensities varied among isomers, enabling their clear differentiation. Additionally, collision-induced dissociation of host-guest complexes at 20 eV shows that the meta isomer forms the most stable complex with β-cyclodextrin and the para isomer forms the least stable complex, which provides additional orthogonal information to differentiate the three isomers. These findings provide a basis for cyclic traveling wave ion mobility and tandem mass spectrometry-based identification and characterization of other isomeric phenyl pyridyl ureas.</p>","PeriodicalId":672,"journal":{"name":"Journal of the American Society for Mass Spectrometry","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2025-05-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143957556","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Rapid Assessment of Samples from Large-Scale Clandestine Synthetic Drug Laboratories by Soft Ionization by Chemical Reaction in Transfer-High-Resolution Mass Spectrometry.","authors":"Maximilian Greif, Tobias Frömel, Thomas P Knepper, Carolin Huhn, Stephan Wagner, Michael Pütz","doi":"10.1021/jasms.5c00006","DOIUrl":"https://doi.org/10.1021/jasms.5c00006","url":null,"abstract":"<p><p>The worldwide ongoing trend of synthetic drug production is also of increasing concern due to enormous amounts of chemical waste produced in clandestine laboratories. Typically, several tons of different types of production waste are stored in numerous containers and need to be characterized after dismantling a laboratory to assess production features, e.g., synthesis route and production scale, and to draw conclusions on the minimum number of batches produced. This forensic assessment is commonly done by a rather laborious gas chromatography - mass spectrometry approach. The aim of this work is to evaluate the suitability of the SICRIT (soft ionization by chemical reaction in transfer) ion source, which is based on the dielectric barrier discharge ionization principle, combined with high-resolution mass spectrometry (HRMS), for the rapid classification of liquid samples from amphetamine production in a seized large-scale clandestine drug laboratory. Among the different sample introduction methods tested, headspace analysis directly into the SICRIT ion source in conjunction with a heated inlet proved to be optimal. Identification of expected target substances (reaction educts, intermediates, byproducts, products) was possible as well as grouping related samples and assigning them to specific synthesis steps by multivariate data analysis in an unsupervised approach. In addition, supervised machine learning algorithms were evaluated to obtain a classification model for the assessment of production waste samples from one dismantled synthetic drug laboratory, and a random forest classifier showed the best performance with an accuracy of 97%. The potential of the novel SICRIT-HRMS approach for the assessment of synthetic drug laboratories was demonstrated.</p>","PeriodicalId":672,"journal":{"name":"Journal of the American Society for Mass Spectrometry","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2025-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143958757","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Maximizing Data Coverage through Eight Sequential Mass Spectrometry Images of a Single Tissue Section","authors":"Erin H. Seeley*,&nbsp;","doi":"10.1021/jasms.5c0003210.1021/jasms.5c00032","DOIUrl":"https://doi.org/10.1021/jasms.5c00032https://doi.org/10.1021/jasms.5c00032","url":null,"abstract":"<p >Typical mass spectrometry imaging (MSI) experiments involve the collection of data from only one class of molecules per section. However, it is often necessary to collect data from different classes of analytes from the same biopsy, and generally, serial sections are used for additional analyte classes. However, differences will be observed between the cells present in each section, especially if the sections are not immediately serial with each other. In this study, a method is presented that allows for 8 mass spectrometry images to be collected sequentially from the same tissue section, including metabolites in positive and negative mode, lipids in positive and negative mode, N-linked glycans, O-linked <i>N</i>-acetylglucosamine, small intact proteins, and tryptic peptides. The order of data collection allows for washing to be used that removes analytes already detected and enhances the signal of subsequently imaged analytes. The collection of multiple images from the same tissue section enables facile coregistration of multiple data sets for evaluation of co- and differential localization across molecular classes.</p>","PeriodicalId":672,"journal":{"name":"Journal of the American Society for Mass Spectrometry","volume":"36 5","pages":"1148–1157 1148–1157"},"PeriodicalIF":3.1,"publicationDate":"2025-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143911034","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Using LDI-MS to Explore Amide Coupling Reactions with Carboxylate Terminated N-Heterocyclic Carbene Monolayers","authors":"Lilian Chinenye Ekowo,&nbsp;Nathaniel L. Dominique,&nbsp;Gurkiran Kaur,&nbsp;David M. Jenkins* and Jon P. Camden*,&nbsp;","doi":"10.1021/jasms.5c0004710.1021/jasms.5c00047","DOIUrl":"https://doi.org/10.1021/jasms.5c00047https://doi.org/10.1021/jasms.5c00047","url":null,"abstract":"<p >N-Heterocyclic carbene (NHC) monolayers on gold display great promise as a platform for biotechnology, which requires biomolecule immobilization to NHC surfaces. The most popular method to couple biomolecules is an amide linkage between a carboxylic acid functionalized NHC and an amine terminated biomolecule. A well-established carboxylic acid terminated NHC-gold system was used as a model system to explore how steric bulk, ring strain, and functionality of amine substrates impact the success of coupling reactions. Here, we deploy laser desorption/ionization mass spectrometry (LDI-MS) to monitor the amide linkage products of the NHC monolayer with amine substrates. Mass spectrometry provides significant advantages when compared to other methods, as it can quickly screen for the successful amide linkage of biomolecules to the NHC monolayer. While we expected the NHC architecture to display a low coupling efficiency with sterically bulky and high ring strain amine substrates, coupling occurred for a wide range of substrates, illustrating the promise of NHCs for biomolecule immobilization. Then, we investigated whether the NHC could effectively couple a model biomolecule, <span>l</span>-lysine. Surprisingly, no evidence of coupling was observed, which prompted a series of experiments exploring the functional group tolerance of coupling reactions on the NHC surfaces. Our LDI-MS results illustrate that coupling reactions of NHC monolayers are intolerant to bifunctional amines bearing a terminal carboxylic acid and that esterification is necessary for successful coupling of amino acids. These general principles of NHC monolayer reactivity will provide a guide for the future design of NHC based biotechnology applications.</p>","PeriodicalId":672,"journal":{"name":"Journal of the American Society for Mass Spectrometry","volume":"36 5","pages":"1182–1190 1182–1190"},"PeriodicalIF":3.1,"publicationDate":"2025-04-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143911356","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Highly Sensitive Chemical Ionization Tandem Mass Spectrometry Method for the Identification of Unsaturated Fatty Acids Derivatized by Dimethyl Disulfide","authors":"Tingxiang Yang,&nbsp;Lerong Qi,&nbsp;Hao Yang,&nbsp;Yihan Xia,&nbsp;Zhen Wang* and Dong Hao Wang*,&nbsp;","doi":"10.1021/jasms.5c0003310.1021/jasms.5c00033","DOIUrl":"https://doi.org/10.1021/jasms.5c00033https://doi.org/10.1021/jasms.5c00033","url":null,"abstract":"<p >Derivatization of unsaturated fatty acids with dimethyl disulfide (DMDS) and analysis by electron ionization mass spectrometry (EIMS) represent a convenient offline method for the identification of double bond positions. However, the presence of overlapping mass spectra from multiple compounds poses significant challenges for spectral interpretation and library matching, leading to ambiguous molecular information and low sensitivity. To overcome the issue, we developed a novel chemical ionization (CI) tandem mass spectrometry method involving the pre-derivatization with DMDS and collisional activation of [M+47]⁺ ions generated in the chemical ion source. The method provides better specificity to the analysis of targeted fatty acids and does not require any customized devices. Further, a multiple reaction monitoring (MRM) version of the method was designed by screening all the diagnostic ions of possible double bond positional isomers, which significantly boosts the sensitivity. Compared to the traditional EIMS method, the new method exhibits a lower limit of detection (LLOD) that is one-tenth or lower. Employing the new method, unusual isomer 18:2(5<i>Z</i>,8<i>Z</i>) was co-analyzed with 18:2(9<i>Z</i>,12<i>Z</i>), and a novel 20:2(7<i>Z</i>,10<i>Z</i>) was characterized in human sebum. Additionally, 16:2(9<i>Z</i>,12<i>Z</i>), an odd-chain omega-3 polyunsaturated fatty acid (21:5n-3) and polymethylene-interrupted isomers, i.e. 22:2(7<i>Z</i>,13<i>Z</i>) and 22:2(7<i>Z</i>,15<i>Z</i>) were identified in seafood and related products. Our method can be readily applied to any GC instrument equipped with tandem MS and is expected to facilitate the discovery and identification of unknown fatty acids from food, clinical, and environmental sources.</p>","PeriodicalId":672,"journal":{"name":"Journal of the American Society for Mass Spectrometry","volume":"36 5","pages":"1158–1166 1158–1166"},"PeriodicalIF":3.1,"publicationDate":"2025-04-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143911357","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Improving MALDI Mass Spectrometry Imaging Performance: Low-Temperature Thermal Evaporation for Controlled Matrix Deposition and Improved Image Quality","authors":"Toufik Mahamdi,&nbsp;Cristina Gomez Serna,&nbsp;Roger Giné,&nbsp;Jordi Rofes,&nbsp;Shad Arif Mohammed,&nbsp;Pere Ràfols,&nbsp;Xavier Correig,&nbsp;María García-Altares,&nbsp;Carsten Hopf,&nbsp;Stefania-Alexandra Iakab and Oscar Yanes*,&nbsp;","doi":"10.1021/jasms.5c0001510.1021/jasms.5c00015","DOIUrl":"https://doi.org/10.1021/jasms.5c00015https://doi.org/10.1021/jasms.5c00015","url":null,"abstract":"<p >The deposition of matrix compounds significantly influences the effectiveness of matrix-assisted laser desorption/ionization (MALDI) Mass Spectrometry Imaging (MSI) experiments, impacting sensitivity, spatial resolution, and reproducibility. Dry deposition methods offer advantages by producing homogeneous matrix layers and minimizing analyte delocalization without the use of solvents. However, refining these techniques to precisely control matrix thickness, minimize heating temperatures, and ensure high-purity matrix layers is crucial for optimizing MALDI-MSI performance. Here, we present a novel approach utilizing low-temperature thermal evaporation (LTE) for organic matrix deposition under reduced vacuum pressure. Our method allows for reproducible control of matrix layer thickness, as demonstrated by linear calibration for two organic matrices, 2,5-dihydroxybenzoic acid (DHB) and 1,5-diaminonaphthalene (DAN). The environmental scanning electron microscopy images reveal a uniform distribution of small-sized matrix crystals, consistently on the sub-micrometer scale, across tissue slides following LTE deposition. Remarkably, LTE serves as an additional purification step for organic matrices, producing very pure layers irrespective of initial matrix purity. Furthermore, stability assessment of MALDI-MSI data from mouse brain sections coated with LTE-deposited DHB or DAN matrix indicates minimal impact on ionization efficiency, signal intensity, and image quality even after storage at −80 °C for 2 weeks, underscoring the robustness of LTE-deposited matrices for MSI applications. Comparative analysis with the spray-coating method highlights several advantages of LTE deposition, including enhanced ionization, reduced analyte diffusion, and improved MSI image quality.</p>","PeriodicalId":672,"journal":{"name":"Journal of the American Society for Mass Spectrometry","volume":"36 5","pages":"1100–1110 1100–1110"},"PeriodicalIF":3.1,"publicationDate":"2025-04-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://pubs.acs.org/doi/epdf/10.1021/jasms.5c00015","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143911270","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effects of Oxygenation on the Reactions of the Iodiranium Ion c-C2H4I+ with Unsaturated Compounds in the Gas Phase","authors":"Samuel C. Brydon*,&nbsp;Jonathan M. White and Richard A. J. O’Hair*,&nbsp;","doi":"10.1021/jasms.4c0049510.1021/jasms.4c00495","DOIUrl":"https://doi.org/10.1021/jasms.4c00495https://doi.org/10.1021/jasms.4c00495","url":null,"abstract":"<p >The potential for ion–molecule reactions to identify alkene functional groups in substrates with increasing oxygenation is explored by using linear ion-trap mass spectrometry. Electrophilic attack by the iodiranium ion, <i>c</i>-C₂H₄I⁺ (<i>m</i>/<i>z</i> 155), proceeds at the collision rate with terminal alkenes RCH═CH₂ (R = <i>n</i>-Pr), allyl ethers (R = MeOCH₂), and nonconjugated methyl esters (R = MeO₂CCH₂), favoring transfer of the iodenium cation to the point of unsaturation by π-ligand exchange. Density functional theory (DFT) calculations at M06-2X-D3/def2-TZVP revealed a single energy well for π-ligand exchange, allowing for a barrierless and hence kinetically favorable reaction pathway. In contrast, ring-opening of the iodiranium ion with subsequent elimination of HI proceeds via a relatively high barrier and is only a minor product channel despite being thermodynamically preferable. Conjugation of the carbon–carbon double bond to an ester group in methyl acrylate had a significant impact on the reaction partitioning with exclusive attack by the carbonyl oxygen to give an allylic stabilized oxonium ion. However, substitution at the point of unsaturation with an inductively donating methyl group enabled the formation of a π-ligand exchange product, which underwent secondary reactions with the neutral. Comparison of the ion–molecule reactions of methyl crotonate, methyl methacrylate, and methyl 3-butenoate with <i>c</i>-C₂H₄I⁺ show this shift in reaction partitioning between ring-opening by the ester carbonyl oxygen and π-ligand exchange is related to the nucleophilicity of the carbon–carbon double bond. The branching ratios of these product channels reveal significant differences between these three structural isomers encompassing conjugated and nonconjugated unsaturated esters.</p>","PeriodicalId":672,"journal":{"name":"Journal of the American Society for Mass Spectrometry","volume":"36 5","pages":"1060–1067 1060–1067"},"PeriodicalIF":3.1,"publicationDate":"2025-04-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143911267","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}