Position Of Double Bond Research Articles

De Novo Structural Elucidation of Acylglycerols by Supercritical Fluid Chromatography and Collision-Induced Dissociation of Electron-Deficient Precursor Ions.

Various mass-spectrometric lipidomics approaches are described to resolve double bond (DB) positions, fatty acid attachments, and sn-position but require dedicated instrumentation or chemical derivatization. In this study, we demonstrate that dopant-assisted atmospheric-pressure photoionization (dAPPI) using chlorobenzene as a dopant generates radical cations (M+.) and [M-H]+ cations of acylglycerols termed Electron Deficient Precursor Ions (EDP). Observed [M-H]+ ions are derived from radical hydrogen abstraction from M+. ions. Collision-induced dissociation of EDP ions allows rule-based de novo annotation of DB positions, fatty acid attachments, and sn-position. Among 33 acylglycerol standards, selective ionization for acylglycerols with ≥1 DB was observed, where acylglycerols with ≤3 DB formed mainly [M-H]+ ions and those with ≥4 M+. ions. EDP-CID generated characteristic intensity ratios of the fragment peaks for sn-positions and double-bond indicative elemental formula losses (EFL) originating from cleavages along the fatty acid alkyl chain with intensity maxima adjunct to DB positions. DB annotation was performed by following EFL series, such as M-CH3(CH2)n for the first DB. For each DB lost, a Δ2H shift is observed (M-CH3(CH2)n Δ2HDB-1) and used for the annotation of following DBs. Additional fragmentation series, indicative of DB positions, were observed after loss of hydroxyl groups or fatty acids (M-FA-CH3(CH2)n). MsRadaR, an R package, was developed allowing to navigate through EDP-CID spectra and visualize relevant EFL series. Last, supercritical fluid chromatography coupled to dAPPI-EDP-CID was applied for the analysis of 57 acylglycerols in linseed oil with complete DB position characterization of 9 diglycerides and 24 triglycerides.

Mechanistic Insights Into the Methoxycarbonylation of Technical Grade Oleochemicals: Catalytical and Structural Analysis of Conjugated Fatty Acid Methyl Esters

ABSTRACTThis study examines the valorization of vegetable oils through Pd‐catalyzed methoxycarbonylation. It investigates the inhibitory effects of polyunsaturated fatty acid methyl esters (PU‐FAME) on catalyst activity, which are frequently reported in academic literature. A particular focus lies on the isomerization of polyunsaturated FAME into conjugated species. In light of the formation of a stable Pd‐allyl complex with polyunsaturated compounds, an investigation of the isomerization products was conducted. NMR and GC analyses demonstrated that isomerization results in the conjugation of double bonds and their relocation toward the ω‐end of the carbon chain. The isomerization results in a thermodynamic distribution of isomerization products for mono‐ and polyunsaturated FAME. The formation of conjugated substrates was confirmed by structural analysis, and oxidative cleavage techniques were employed to determine the precise distribution of double bond positions. The findings offer insight into how conjugated PU‐FAME inhibit methoxycarbonylation, thereby limiting the valorization of vegetable oils.Practical Applications: This study provides further insights into the homogeneous catalyzed formation of conjugated methyl linoleate using a palladium catalyst. Combining different analytic techniques and chemical modification provides a novel approach for determining double bond positions in fatty acids. Furthermore, these findings may facilitate the design of new catalysts for the methoxycarbonylation process, thereby preventing the formation of conjugated intermediates. This could result in an efficient conversion of technical‐grade oils. Additionally, the production of a diverse range of isomers for subsequent functionalization is demonstrated.

Stereoselective Reaction Enabling Simultaneous Analysis of Carbon-Carbon Double-Bond Configuration and the Position of Monounsaturated Fatty Acids through UHPLC-ESI-MRM-MS.

Monounsaturated fatty acids (MUFA) are an important class of nutrients and are involved in lipid metabolism. The positions of the C=C bond and cis-trans isomerism have a significant influence on their physiological activity. However, simultaneously detecting these two structural properties has been challenging due to multiple isomers of MUFA. In this study, we developed a method that involved an N-aminophthalimide (PhthNH2) derivatization of the C=C bond in MUFA, followed by analysis using ultrahigh-performance liquid chromatography-electrospray ionization-multiple reaction monitoring mass spectrometry (UHPLC-ESI-MRM-MS) technology to achieve analysis of cis-trans isomers and positional isomers of the C=C bond. The derivatives of cis-trans isomers of the C=C bond were well separated in UHPLC, and their corresponding C=C bond positions were deduced from characteristic fragment ions in tandem mass spectrometry. With our method, we found MUFA with different double-bond positions and cis-trans isomers in several samples, including mouse kidney, butter, etc., achieving qualitative analysis and relative quantitation. This method is expected to be applied by more researchers in lipidomics studies in the future.

Complete Polar Lipid Profile of Kefir Beverage by Hydrophilic Interaction Liquid Chromatography with HRMS and Tandem Mass Spectrometry

Kefir, a fermented milk product produced using kefir grains, is a symbiotic consortium of bacteria and yeasts responsible for driving the fermentation process. In this study, an in-depth analysis of kefir’s lipid profile was conducted, with a focus on its phospholipid (PL) content, employing liquid chromatography with high-resolution mass spectrometry (LC-HRMS). Nearly 300 distinct polar lipids were identified through hydrophilic interaction liquid chromatography (HILIC) coupled with electrospray ionization (ESI) and Fourier-transform orbital-trap MS and linear ion-trap tandem MS/MS. The identified lipids included phosphatidylcholines (PCs), lyso-phosphatidylcholines (LPCs), phosphatidylethanolamines (PEs) and lyso-phosphatidylethanolamines (LPEs), phosphatidylserines (PSs), phosphatidylglycerols (PGs), and phosphatidylinositols (PIs). The presence of lysyl-phosphatidylglycerols (LyPGs) was identified as a key finding, marking a lipid class characteristic of Gram-positive bacterial membranes. This discovery highlights the role of viable bacteria in kefir and underscores its probiotic potential. The structural details of minor glycolipids (GLs) and glycosphingolipids (GSLs) were further elucidated, enriching the understanding of kefir’s lipid complexity. Fatty acyl (FA) composition was characterized using reversed-phase LC coupled with tandem MS. A mild epoxidation reaction with meta-chloroperoxybenzoic acid (m-CPBA) was performed to pinpoint double-bond positions in FAs. The dominant fatty acids were identified as C18:3, C18:2, C18:1, C18:0 (stearic acid), C16:0 (palmitic acid), and significant levels of C14:0 (myristic acid). Additionally, two isomers of FA 18:1 were distinguished: ∆9-cis (oleic acid) and ∆11-trans (vaccenic acid). These isomers were identified using diagnostic ion pairs, retention times, and accurate m/z values. This study provides an unprecedented level of detail on the lipid profile of kefir, shedding light on its complex composition and potential nutritional benefits.

OzNOxESI: A Novel Mass Spectrometry Ion Chemistry for Elucidating Lipid Double-Bond Regioisomerism in Complex Mixtures.

Double bond (C═C) position isomerism in unsaturated lipids can indicate abnormal lipid metabolism and pathological conditions. Novel chemical derivatization and mass spectrometry-based techniques are under continuing development to provide more accurate elucidation of lipid structure in finer structural detail. Here, we introduce a new ion chemistry for annotating lipid C═C positions, which is highly efficient for liquid chromatography-mass spectrometry-based lipidomics. This ion chemistry relies on the online derivatization of lipid C═C with ozone and nitrogen oxides upon fragmentation by tandem mass spectrometry, yielding characteristic product ions capable of unambiguously annotating C═C regioisomers. The new workflow was thoroughly evaluated with various glycerophospholipids and fatty acids and applied to human plasma lipid extract, successfully identified and quantified 270 glycerophospholipid and 36 fatty acid C═C isomers with an in-house developed software, OzNOx Companion, for automated data analysis.

Electron Transfer Dissociation of Alkali-Cationized Phosphatidylcholines Allows Easy Double Bonds and sn-1/sn-2 Localizations.

The emergence of new mass spectrometry (MS) dissociation methods has highlighted lipid isomers as new biomarkers. Only a few commercial methods without derivatization are available to characterize phosphatidylcholines (PCs) at the isomeric level. We propose to use electron transfer dissociation (ETD) as a method to determine the position of both double bonds and stereo numbering (sn) on glycerol for PC species. Doubly charged PCs were analyzed using alkali salts to promote the formation of [PC + 2Alk]2+ species. ETD-MS2 experiments were performed using a quadrupole ion trap mass spectrometer with an ESI source to annotate sn-positions. ETD-CID-MS3 experiments were then done on ETnoD [M + 2Alk]+• or [M + 2Alk-N(CH3)3]+• species to localize double bond positions. Density functional theory (DFT) calculations and cyclic ion mobility spectrometry c-IMS-MS/MS experiments were used to support fragmentation assumptions. ETD-MS2 experiments exhibit a systematic sn-2 favorable cleavage, allowing sn-positioning through a radical cation-driven mechanism supported by DFT calculations. This behavior contrasts with CID experiments, in which the initial positioning of alkali cations influences ester bond cleavage, as shown by c-IMS-MS/MS experiments. The dissociation process studied for ETD-CID-MS3 experiments on 10 different PC isomers allowed us to localize double bonds for either monounsaturated or polyunsaturated species. The dissociation rules established for ETD-MS2 and ETD-CID-MS3 experiments on PC isomers enable their annotation at the isomeric level without instrumental modification or complex sample preparation. This method could be easily coupled to LC separation using post-column introduction of an alkali salt for complex mixture analysis.

New Antioxidant Caffeate Esters of Fatty Alcohols Identified in Robinia pseudoacacia.

The stem bark of black locust (Robinia pseudoacacia L.) was extracted, and nine antioxidant compounds (R1-R9) were detected by high-performance thin-layer chromatography combined with the radical scavenging 2,2-diphenyl-1-picrylhydrazyl (DPPH•) assay, multi-detection, and heated electrospray high-resolution mass spectrometry. For structure elucidation, the methanolic crude extract was fractionated by solid-phase extraction, and the compounds were isolated by reversed-phase high-performance liquid chromatography with diode array detection. The structures of isolated compounds were elucidated by nuclear magnetic resonance and attenuated total reflectance Fourier-transform infrared spectroscopy as well as gas chromatography-mass spectrometry to determine the double bond position. 3-O-Caffeoyl oleanolic acid (R1), oleyl (R2), octadecyl (R3), gadoleyl (R4), eicosanyl (R5), (Z)-9-docosenyl (R6), docosyl (R7), tetracosyl (R8), and hexacosanyl (R9) caffeates were identified. While R1 has been reported in R. pseudoacacia stem bark, the known R3, R5, R7, R8, and R9 are described for the first time in this species, and the R2, R4, and R6 are new natural compounds. All nine caffeates demonstrated antioxidant activity. The antioxidant effects of the isolated compounds R1-R8 were quantified by a microplate DPPH• assay, with values ranging from 0.29 to 1.20 mol of caffeic acid equivalents per mole of isolate.

MS-DIAL 5 multimodal mass spectrometry data mining unveils lipidome complexities

Lipidomics and metabolomics communities comprise various informatics tools; however, software programs handling multimodal mass spectrometry (MS) data with structural annotations guided by the Lipidomics Standards Initiative are limited. Here, we provide MS-DIAL 5 for in-depth lipidome structural elucidation through electron-activated dissociation (EAD)-based tandem MS and determining their molecular localization through MS imaging (MSI) data using a species/tissue-specific lipidome database containing the predicted collision-cross section values. With the optimized EAD settings using 14 eV kinetic energy, the program correctly delineated lipid structures for 96.4% of authentic standards, among which 78.0% had the sn-, OH-, and/or C = C positions correctly assigned at concentrations exceeding 1 μM. We showcased our workflow by annotating the sn- and double-bond positions of eye-specific phosphatidylcholines containing very-long-chain polyunsaturated fatty acids (VLC-PUFAs), characterized as PC n-3-VLC-PUFA/FA. Using MSI data from the eye and n-3-VLC-PUFA-supplemented HeLa cells, we identified glycerol 3-phosphate acyltransferase as an enzyme candidate responsible for incorporating n-3 VLC-PUFAs into the sn1 position of phospholipids in mammalian cells, which was confirmed using EAD-MS/MS and recombinant proteins in a cell-free system. Therefore, the MS-DIAL 5 environment, combined with optimized MS data acquisition methods, facilitates a better understanding of lipid structures and their localization, offering insights into lipid biology.

Characterization of Opioid Agonist Morphine Derivatives with Emphasis on Medicinal Chemistry.

Relieving severe pains is an unmet medical need, in which opioids are of prime importance and in the focus of pharmaceutical companies. The objective of this study is to characterize the physicochemical properties, namely basicity, lipophilicity and permeability of thirty opioid ligands, which include eleven newly synthesized compounds. pH-potentiometry and the shake-flask method were used for the characterization of species-specific basicity and lipophilicity. The effective permeability was determined using a brain-specific parallel artificial membrane permeability assay. Structural modifications, namely O-methylation in position 3, isomerization in position 6, saturation of the double bond in position 7, 14-hydroxylation, and the substitution of N-(β-phenylethyl) and N-cyclobutylmethyl side chains all have various effects on these physicochemical properties, and these are explained and compared to computationally predicted values. Computational predictions inadequately capture hydrogen bond formation with the tertiary amino group in case of 14-hydroxylation, just as the effects of hydroxy oxidation at position 6 and N-methyl substitution with N-(β-phenylethyl). The relationship between lipophilicity, permeability and potency is presented by lipophilic efficiency plots that reveal the most promising compounds. This study emphasizes the importance of experimental determination of these essential physicochemical parameters, furthermore, it can contribute to a more thorough understanding of the pharmacokinetic properties.

Determination of double bond positions in unsaturated fatty acids by pre-column derivatization with dimethyl and dipyridyl disulfide followed by LC-SWATH-MS analysis.

Comprehensive in-depth structural characterization of free mono-unsaturated and polyunsaturated fatty acids often requires the determination of carbon-carbondouble bond positions due to their impact on physiological properties and relevance in biological samples or during impurity profiling of pharmaceuticals. In this research, we report on the evaluation of disulfides as suitable derivatization reagents for the determination of carbon-carbondouble bond positions of unsaturated free fatty acids by UHPLC-ESI-QTOF-MS/MS analysis and SWATH (sequential windowed acquisition of all theoretical mass spectra) acquisition. Iodine-catalyzed derivatization of C = C double bonds with dimethyl disulfide (DMDS) enabled detection of characteristic carboxy-terminal MS2 fragments for various fatty acids in ESI negative mode. The determination of double bond positions of fatty acids with up to three double bonds, the transfer of the method to plasma samples, and its limitations have been shown. To achieve charge-switching for positive ion mode MS-detection, derivatization with 2,2'-dipyridyldisulfide (DPDS) was investigated. It enabled detection of both corresponding characteristic omega-end- and carboxy-end-fragments for fatty acids with up to two double bonds in positive ion mode. It provides a straightforward strategy for designing MRM transitions for targeted LC-MS/MS assays. Both derivatization techniques represent a simple and inexpensive way for the determination of double bond positions in fatty acids with low number of double bonds. No adaptation of MS hardware is required and the specific isotopic pattern of resulting sulfur-containing products provides additional structural confirmation. This reaction scheme opens up the avenue of structural tuning of disulfide reagents beyond DMDS and DPDS using reagents like cystine and analogs to achieve enhanced performance and sensitivity.

Geometric isomerization of dietary monounsaturated fatty acids by a cis/trans fatty acid isomerase from Pseudomonas putida KT2440

Pseudomonas putida KT2440 encodes a defense system that rigidifies membranes by a cytochrome c-type cis/trans fatty acid isomerase (CTI). Despite its potential as an industrial biocatalyst for directly regulating the geometric isomerism of monounsaturated fatty acids, its original catalytic and structural properties have remained elusive. In this study, the catalytic nature of wild-type CTI purified P. putida KT2440 against dietary monounsaturated fatty acids was investigated. It showed substrate preference for palmitoleic acid (C16:1, cis-Δ9), along with substrate promiscuity with chain length and double bond position (palmitoleic acid>cis-vaccenic acid>oleic acid). Under determined optimum reaction conditions, its catalytic efficiency (kcat/Km) was evaluated as 5.13×102M-1·sec-1 against palmitoleic acid. Furthermore, computational predictions of the protein structure revealed its monoheme cytochrome c-type domain and a parasol-like transmembrane domain, suggesting its catalytic mode of action. For effective cis/trans isomerization, the ethylene double bond of monounsaturated fatty acids should be precisely positioned at the heme center of CTI, indicating that its substrate specificity can be determined by the alkyl chain length and the double bond position of the fatty acid substrates. These findings shed light on the potential of CTI as a promising biocatalyst for the food and lipid industry.

Identification and quantitation of carbon–carbon double bond isomers of fatty acid in livestock and poultry meat

Livestock and poultry meat is one of the main consumption sources of fatty acids (FAs) in China. FAs are the main component of lipids and essential nutrients for the human body. The location of carbon-carbon double bond (CC) in unsaturated fatty acids (UFAs) significantly affects the nutrition and flavor quality of meat products. This study established an analytical method for identifying the CC positions of UFAs based on the Paternò-Büchi (PB) reaction using ultra-high performance liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF). The FA extract was derivatized with 2-acetylpyridine under ultraviolet light at 254nm. The derivatized FA was then analyzed using targeted MS/MS mode in positive electrospray ionization. Limits of detection (LOD) and limits of quantitation (LOQ) of 21 UFAs were 0.004-0.680 and 0.013-2.267μg/L, respectively. Furthermore, for the diagnostic ions at the same functional group terminal fragmented from derivatives of FA CC isomers, the abundance ratio was linear with that of the corresponding content, which could be applied to non-targeted screening of CC positions in FAs. Based on this method, a total of 28 UFAs were screened in five types of livestock and poultry meats in this study. Among them, four isomers of C17:1, four of C18:1, two of C18:2, two of C20:3 and two of C22:5 were identified. The precise identification and quantitation of the double bond positions of fatty acids will be of great significance for the exploration of the nutritional components in livestock and poultry meat.

Making OzID go FFASTer: Combining stable-isotope tagging with ozone-induced dissociation to uncover changes in fatty acid unsaturation within neurosecretory cells

Making OzID go FFASTer: Combining stable-isotope tagging with ozone-induced dissociation to uncover changes in fatty acid unsaturation within neurosecretory cells

The subchronic toxicity of higher olefins in Han Wistar rats

Higher olefins (HO) are a category of unsaturated hydrocarbons widely used in industry applications to make products essential for daily human life. Establishing safe exposure limits requires a solid data matrix that facilitates understanding of their toxicological profile. This in turn allows for data to be read across to other members of the category, which are structurally similar and have predictable physico-chemical properties. Five independent subchronic oral toxicity studies were conducted in Wistar rats with Oct-1-ene, Nonene, branched, Octadec-1-ene, Octadecene and hydrocarbon C12-30, olefin-rich, ethylene polymn. by product, at doses ranging from 20 to 1000 mg/kg bw. These HO were selected considering gut absorption, carbon chain length, double-bond position and carbon backbone structural variations. Generally, limited and non-adverse toxicity effects were observed at the end of the treatment for short carbon chain HO. For instance, alpha 2u-globulin nephropathy in the male rats and liver hypertrophy. No clear trend in systemic toxicity was linked to the double-bond position. Key factors for hazard assessment include absorption, carbon chain length, and branching, with Nonene, branched, identified as the worst-case substance. Taken together, the no observed adverse effect level (NOAEL) of each HO in these subchronic studies was set at the highest dose tested.

Stability of Medium-Ring Cyclic Unsaturated Carbonyl Compounds: Direct Access to Unsaturated Ketones with C-C Double Bonds at Distal Positions via Transfer Dehydrogenation of Alicyclic Ketones.

Medium-ring cyclic compounds have characteristic distortions. For alicyclic enones, conjugated enones are known to be less stable than unconjugated enones. In this study, the relative stability of cycloalkenones with varied C-C double bond positions with C6-C12 rings was theoretically investigated to reveal that C8-C12 cycloalkenones prefer the unconjugated isomer. Furthermore, direct access to distal unsaturated cycloalkenones has been accomplished by transfer dehydrogenation of cycloalkanones catalyzed by iridium complexes.

Cross-Validation of Lipid Structure Assignment Using Orthogonal Ion Activation Modalities on the Same Mass Spectrometer.

The onset and progression of cancer is associated with changes in the composition of the lipidome. Therefore, better understanding of the molecular mechanisms of these disease states requires detailed structural characterization of the individual lipids within the complex cellular milieu. Recently, changes in the unsaturation profile of membrane lipids have been observed in cancer cells and tissues, but assigning the position(s) of carbon-carbon double bonds in fatty acyl chains carried by membrane phospholipids, including the resolution of lipid regioisomers, has proven analytically challenging. Conventional tandem mass spectrometry approaches based on collision-induced dissociation of ionized glycerophospholipids do not yield spectra that are indicative of the location(s) of carbon-carbon double bonds. Ozone-induced dissociation (OzID) and ultraviolet photodissociation (UVPD) have emerged as alternative ion activation modalities wherein diagnostic product ions can enable de novo assignment of position(s) of unsaturation based on predictable fragmentation behaviors. Here, for the first time, OzID and UVPD (193 nm) mass spectra are acquired on the same mass spectrometer to evaluate the relative performance of the two modalities for lipid identification and to interrogate the respective fragmentation pathways under comparable conditions. Based on investigations of lipid standards, fragmentation rules for each technique are expanded to increase confidence in structural assignments and exclude potential false positives. Parallel application of both methods to unsaturated phosphatidylcholines extracted from isogenic colorectal cancer cell lines provides high confidence in the assignment of multiple double bond isomers in these samples and cross-validates relative changes in isomer abundance.

Structural characterization of wax esters using ultraviolet photodissociation mass spectrometry

Wax esters play critical roles in biological systems, serving functions from energy storage to chemical signaling. Their diversity is attributed to variations in alcohol and acyl chains, including their length, branching, and the stereochemistry of double bonds. Traditional analysis by mass spectrometry with collisional activations (CID, HCD) offers insights into acyl chain lengths and unsaturation level. Still, it falls short in pinpointing more nuanced structural features like the position of double bonds. As a solution, this study explores the application of 213-nm ultraviolet photodissociation (UVPD) for the detailed structural analysis of wax esters. It is shown that lithium adducts provide unique fragments as a result of Norrish and Norrish-Yang reactions at the ester moieties and photoinduced cleavages of double bonds. The product ions are useful for determining chain lengths and localizing double bonds. UVPD spectra of various wax esters are presented systematically, and the effect of activation time is discussed. The applicability of tandem mass spectrometry with UVPD is demonstrated for wax esters from natural sources. The UHPLC analysis of jojoba oil proves the compatibility of MS2 UVPD with the chromatography time scale, and a direct infusion is used to analyze wax esters from vernix caseosa. Data shows the potential of UVPD and its combination with CID or HCD in advancing our understanding of wax ester structures.Graphical

Catalyst-Free Dynamic Covalent C=C/C=N Metathesis Reaction for Associative Covalent Adaptable Networks.

Covalent adaptable networks (CANs), leveraging the dynamic exchange of covalent bonds, emerge as a promising material to address the challenge of irreversible cross-linking in thermosetting polymers. In this work, we explore the introduction of a catalyst-free and associative C=C/C=N metathesis reaction into thermosetting polyurethanes, creating CANs with superior stability, solvent resistance, and thermal/mechanical properties. By incorporating this dynamic exchange reaction, stress-relaxation is significantly accelerated compared to imine-bond-only networks, with the rate adjustable by modifying substituents in the ortho position of the dynamic double bonds. The obtained plasticity enables recycle without altering the chemical structure or mechanical properties, and is also found to be vital for achieving shape memory functions with complex spatial structures. This metathesis reaction as a new dynamic crosslinker of polymer networks has the potential to accelerate the ongoing exploration of malleable and functional thermoset polymers.

Catalyst‐Free Dynamic Covalent C=C/C=N Metathesis Reaction for Associative Covalent Adaptable Networks

AbstractCovalent adaptable networks (CANs), leveraging the dynamic exchange of covalent bonds, emerge as a promising material to address the challenge of irreversible cross‐linking in thermosetting polymers. In this work, we explore the introduction of a catalyst‐free and associative C=C/C=N metathesis reaction into thermosetting polyurethanes, creating CANs with superior stability, solvent resistance, and thermal/mechanical properties. By incorporating this dynamic exchange reaction, stress‐relaxation is significantly accelerated compared to imine‐bond‐only networks, with the rate adjustable by modifying substituents in the ortho position of the dynamic double bonds. The obtained plasticity enables recycle without altering the chemical structure or mechanical properties, and is also found to be vital for achieving shape memory functions with complex spatial structures. This metathesis reaction as a new dynamic crosslinker of polymer networks has the potential to accelerate the ongoing exploration of malleable and functional thermoset polymers.

Structural characterization of sphingomyelins from tissue using electron-induced dissociation.

Sphingomyelins (SMs) and resulting metabolic products serve important functional and cell signaling roles and can act as potential biomarkers and therapeutic targets in many pathological disorders. SMs each contain a sphingoid base, an amide-linked fatty acyl chain, and a phosphocholine headgroup. Despite these simple building blocks, variations and modifications of both the sphingoid base and the fatty acyl chain result in a diverse array of structurally complicated SM compounds. Conventional tandem mass spectrometry (MS/MS) using the collision-induced dissociation (CID) method only provides limited structural information, necessitating other tools to unravel the structural complexity of these lipids. We utilize electron-induced dissociation (EID) and sequential CID/EID approaches to elucidate detailed structural features of SMs. Integrating the CID/EID method into an imaging MS workflow enables accurate identification of SMs directly from kidney tissue. The application of EID enables identification of SMs at the molecular species level, identifying the sphingosine base and the amide-linked fatty acyl chains. Furthermore, removal of the phosphocholine headgroup via CID followed by sequential EID in an MS3 analysis (CID/EID) enhances the structural information obtained. CID/EID provides diagnostic fragmentation patterns revealing the hydroxylation site and double bond position in both the sphingosine base and amide-linked fatty acyl chains. Detailed structural information of SMs from synthetic standards and biological tissue samples is obtained using an alternative electron-based dissociation method. Accurate characterization of SMs promises to better inform studies of tissue biochemistry, lipid metabolism, and molecular pathology.