Distinctive MS/MS Fragmentation Pathways of Glycopeptide‐Generated Oxonium Ions Provide Evidence of the Glycan Structure

Post‐translational glycosylation of proteins play key roles in cellular processes and the site‐specific characterisation of glycan structures is critical to understanding these events. Given the challenges regarding identification of glycan isomers, glycoproteomic studies generally rely on the assumption of conserved biosynthetic pathways. However, in a recent study, we found characteristically different HexNAc oxonium ion fragmentation patterns that depend on glycan structure. Such patterns could be used to distinguish between glycopeptide structural isomers. To acquire a mechanistic insight, deuterium‐labelled glycopeptides were prepared and analysed. We found that the HexNAc‐derived m/z 126 and 144 oxonium ions, differing in mass by H₂O, had completely different structures and that high‐mannose N‐glycopeptides generated abundant Hex‐derived oxonium ions. We describe the oxonium ion decomposition mechanisms and the relative abundance of oxonium ions as a function of collision energy for a number of well‐defined glycan structures, which provide important information for future glycoproteomic studies.     

Mannose7 Glycan Isomer Characterization by IMS-MS/MS Analysis

The isomers of the Man₇GlcNAc₂ glycan obtained from bovine ribonuclease B have been characterized by ion mobility spectrometry-tandem mass spectrometry (IMS-MS/MS). In these experiments, [Man7 + 2Na]²⁺ precursors having different mobilities are selected by ion mobility spectrometry and analyzed by MS/MS techniques in an ion trap. The fragmentation spectra obtained for various precursor ions are specific, suggesting the isolation or enrichment of different glycan isomers. One fragment ion with a mass-to-charge ratio (m/z) of 903.8 is found to correspond to the loss of an internal mannose residue of a specific isomer. Extracted fragment ion drift time distributions (XFIDTDs) yield distinctive precursor ion drift time profiles indicating the existence of four separate isomers as proposed previously.     

Characterization of Glycan Structures of Chondroitin Sulfate-Glycopeptides Facilitated by Sodium Ion-Pairing and Positive Mode LC-MS/MS

Purification and liquid chromatography-tandem mass spectrometry (LC-MS/MS) characterization of glycopeptides, originating from protease digests of glycoproteins, enables site-specific analysis of protein N- and O-glycosylations. We have described a protocol to enrich, hydrolyze by chondroitinase ABC, and characterize chondroitin sulfate-containing glycopeptides (CS-glycopeptides) using positive mode LC-MS/MS. The CS-glycopeptides, originating from the Bikunin proteoglycan of human urine samples, had ΔHexAGalNAcGlcAGalGalXyl-O-Ser hexasaccharide structure and were further substituted with 0-3 sulfate and 0-1 phosphate groups. However, it was not possible to exactly pinpoint sulfate attachment residues, for protonated precursors, due to extensive fragmentation of sulfate groups using high-energy collision induced dissociation (HCD). To circumvent the well-recognized sulfate instability, we now introduced Na⁺ ions to form sodiated precursors, which protected sulfate groups from decomposition and facilitated the assignment of sulfate modifications. Sulfate groups were pinpointed to both Gal residues and to the GalNAc of the hexasaccharide structure. The intensities of protonated and sodiated saccharide oxonium ions were very prominent in the HCD-MS2 spectra, which provided complementary structural analysis of sulfate substituents of CS-glycopeptides. We have demonstrated a considerable heterogeneity of the bikunin CS linkage region. The realization of these structural variants should be beneficial in studies aimed at investigating the importance of the CS linkage region with regards to the biosynthesis of CS and potential interactions to CS binding proteins. Also, the combined use of protonated and sodiated precursors for positive mode HCD fragmentation analysis will likely become useful for additional classes of sulfated glycopeptides.

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金属离子与腺嘌呤异构体复合物的稳定性

在B3LYP/6-311++G**//6-31+G*基组水平上结合PCM模型系统的优化了气相和液相环境中14种腺嘌呤异构体与四种金属离子(Na+,K+,Mg2+,Ca2+)形成的132个稳定复合物。通过能量对比,得到了所有复合物异构体在气液两相中的稳定性顺序及不同金属离子与同一异构体形成的复合物的能量排序,首次给出了液相中这些不同金属离子复合物的最稳定结构。结果发现溶剂效应导致了液相中的复合物稳定性顺序与气相中的相比发生了很大变化;同一异构体与不同金属离子形成的复合物其稳定性在排序中也变化很大。对于这些变化,本文分别从金属离子与腺嘌呤的复合物在气相中的结合能(EBE)及在液相中的溶质溶剂相互作用能(Epol)能等方面进行了系统的阐述     

Identification and Structural Elucidation of Corrosion Inhibiting Long-Chain N-1-Alkyl-1,3-propanediamines by GC–MS

Gas chromatography–mass spectrometry has been used to identify long-chain (C₈–C₁₈) N-1-alkyl-1,3-propanediamines after derivatization with trifluoroacetic anhydride. Electron impact ionization and negative chemical ionization mass spectra of trifluoroacetylated derivatives of the identified N-1-alkyl-1,3-propanediamines are presented for the first time. The corrosion inhibiting long-chain N-1-alkyl-1,3-propanediamines were applied in the preparation and investigation of a new anticorrosive and antifouling formulation for water–steam circuit of energy systems in the power industry. Using the GC–MS data, it was possible to identify residues of the N-1-alkyl-1,3-propanediamines in complex samples of boiler water from the power plant after solid-phase extraction and acylation.     

MS／MS Study of Deoxydinucleotides Bound with Alkali—metal Ions Using ESI—MS

Positive ion ESI-MS has been used to examine the fragmentation pathways of the complex ions of deoxydinucleotides with H^ ,Na^ ,K^ by LCQ instrument.It had been found that the dissociation Varied markedly due to the differences of the base sequence.The alkali-metal ion binding site and the charcaterization of dissociation were directed by the size of metal ion,the sequesce of base and the steric hindrance.     

Structural identification of degradants of moexipril by LC–MS/MS

A gradient LC–MS method was developed for the identification and characterization of degradants of moexipril using liquid chromatography electrospray ionization tandem mass spectrometry (LC/ESI‐MS/MS). Moexipril was subjected to hydrolysis (acid, base and neutral), oxidation, photolytic and thermal degradation conditions as mentioned in ICH guidelines Q1A (R2). The drug degraded under hydrolysis, oxidation and photolytic conditions, but it was stable under thermal conditions. In total, five degradants were formed and separated on an Agilent XDB C‐18 column (4.6 × 150 mm, 5 μm) in a gradient elution method. Four degradants ( D1 , D2 , D4 and D5 ) under acidic conditions, three degradants ( D2 , D3 and D4 ) under basic conditions and three degradants ( D1 , D4 and D5 ) under neutral and oxidative stress conditions were formed. In addition, two degradants ( D4 and D5 ) were formed under photolytic stress conditions. To elucidate the structures of degradants, fragmentation of moexipril and its degradants was studied using LC–MS/MS experiments and accurate mass measurements (HRMS) data. The fragment ions in the product ion tandem mass spectra of all the degradants were compared with those of moexipril and assigned the probable structures for the degradants.     

乳腺癌代谢物组模式特征发现方法及HPLC/M S/M S分析

提出一种基于单独最优特征组合和BP神经网络的代谢物组模式特征发现方法,并用其寻找到尿样中与乳腺癌最为相关的4种核苷,组成一组特异性检测参数.经HPLC/MS/MS联用法鉴定,它们是乳清酸核苷、1-甲酰化腺苷、S-腺苷-L-蛋氨酸及N²-甲酰化鸟苷.将这4种核苷作为输入变量,用BP神经分类网络建立乳腺癌诊断模型.留一法交叉验证和独立验证结果表明,该模型预测准确率达到90%以上.     

HS/GC-MS/MS法检测海产品中二甲苯

建立了顶空进样/气相色谱-串联三重四极杆质谱(HS/GC-MS/MS)检测海产品中3种二甲苯同分异构体的方法。海产品经90℃温育和振荡平衡40 min顶空进样,HP-INNOWax色谱柱分离,程序升温,在多反应监测(MRM)模式下进行GC-MS/MS检测,外标法定量。结果表明,3种二甲苯同分异构体在5.0~100.0μg/kg范围内呈良好线性,相关系数均在0.99以上,方法检出限为2.5μg/kg,定量下限为5.0μg/kg。黄鱼样品在6.0、15.0、50.0μg/kg加标水平下的平均回收率为89.6%~112.4%,相对标准偏差(RSD)不大于11.5%。采用建立的方法测定了不同海产品中二甲苯同分异构体的含量。该法操作简单、定性准确、灵敏度较高,适于海产品中二甲苯残留量的测定。     

Structural characterization and sequence distributions of polysiloxanes using pyrolysis MS/MS

Novel polysiloxanes, with 4-(dialkylamino)pyridine substituents, are characterized by pyrolysis tandem mass spectrometry. These polymers form abundant cyclic oligomeric ions under both desorption electron ionization (DEI) and desorption chemical ionization (DCI) conditions. Product MS/MS spectra of the cyclic ions reveal characteristic fragmentations under low energy collision activated dissociation. Protonated cyclic oligomers higher than the pentamer are mainly due to the proton bound dimers of lower oligomeric units. The cyclic oligomers are shown to have proton affinities greater than 1000 kJ/mole. It is proposed that thermal depolymerization occurs through an intramolecular siloxane bond rearrangement, which is in agreement with a previously proposed "loop mechanism". Markovian statistical calculations are applied to the DCI mass spectral data in order to determine the sequence distribution of siloxane copolymers. Application of this method show that the monomers in the copolymers examined are non-randomly distributed.     

Discrimination of Structural Isomers of Aromatic Compounds with EI Mass Spectra and Their Ionization Efficiency Curves of Dehydrogenated Fragment Ions

Wehavereportedtheeffectofovercrowdinginthemassspectfaofcondensedpolycyclicaromaticcompounds'-'.Themassdifferencebetweenamolecularionandthemostintensefragmentionintheionfamilyofthehighestvalencecorrespondstothenumberofovercrowdedhydrogenatomsdetachingfromtheparention,andtheirmasspatternsaredifferentwiththetypeofovercrowding,i.e.fjord-orcrab-likeovercrowding.Thehighabundanceofspecificfragmentionsat70Vwascorrelatedwiththeloweringoftheirappearanceenergies.Hereweinvestigatedthemassspectraandthemech…     

Differentiation of Four Pairs of Isomers by Comparing Their Relative Abundances of Fragment Ions

Based on the LC-ESI/MSn technique, the four pairs of isomers of psoralen and isopsoralen, imperatorin and isoimperatorin, neohesperidin and hesperidin, naringin and narirutin were distinguished mainly by comparison of the relative abundances of their major fragment ions. Because of the effect of the hydrogen on the C8 of psoralen, the intensity of the fragment ion formed by the loss of CO2 was relatively increased. By comparing the abundance of the product ions formed by the loss of CO and 2CO, the isomers ...     

溶剂诱导黑色素瘤抗原基因-2特定表位多肽异构的LC/MS研究

 研究乙醇、甲醇两种常用溶剂系统对固相合成的黑色素瘤抗原基因 2 (MAGE 2 )的特定表位多肽 (171 179)异构的影响。分别运用乙醇、甲醇溶剂体系以及极性溶剂二甲基亚砜 (DMSO)作对照预处理固相合成的黑色素瘤抗原特异性MAGE 2表位多肽 (171～ 179) ,然后用反相高效液相色谱 /质谱联用技术 (RP HPLC/MS)对合成的表位多肽的m/z进行Q1正离子监测扫描分析 ,观察其在不同溶剂系统预处理下的异构情况 ,以选择合理的预处理条件。结果发现采用乙醇及甲醇溶样时MAGE 2表位多肽有异构体产生 ,极性溶剂DMSO溶样的表位多肽未有异构现象发生。     

利用HPLC-ESI-MS/MS区分黄芩中黄酮C-苷异构体的研究

采用HPLC-ESI-MS/MS联用技术区分了黄芩中两种互为同分异构体的黄酮C-苷类化合物5,7-OH-6-C-阿拉伯糖-8-C-葡萄糖黄酮和5,7-OH-6-C-葡萄糖-8-C-阿拉伯糖黄酮.阐述了黄酮C-苷类化合物同分异构体的电喷雾串联质谱(ESI-MSⁿ)的特征碎裂规律,证明了[M-H-60]^-,[M-H-90]^-及[M-H-120]^-离子是其特征离子.实验结果表明,对于C-6位五碳糖取代和C-8位六碳糖取代的黄酮C-苷二级串联质谱产生的[M-H-60]^-离子(^0,3₅X),其丰度一般大于50%;而对于C-6位六碳糖取代和C-8位五碳糖取代的黄酮C-苷二级串联质谱产生的[M-H-60]^-离子(^0,3₅X),其丰度一般小于50%.据此可区分两种互为同分异构体的黄酮C-苷类化合物.     

Selective detection and identification of phosphopeptides by dansyl MS/MS/MS fragmentation

Protein phosphorylation regulates many cellular processes and pathways, such as cell cycle progression, signal transduction cascades and gene expression. Selective detection of phosphopeptides from proteolytic digests is a challenging and highly relevant task in many proteomics applications. Often phosphopeptides are present in small amounts and need selective isolation or enrichment before identification. Here we report a novel approach to label selectively phospho-Ser/-Thr residues by exploiting the features of a novel linear ion trap mass spectrometer. Using dansyl labelling and MS3 fragmentation, we developed a method useful for the large-scale proteomic profiling of phosphorylation sites. The new residues in the sequence were stable and easily identifiable under general conditions for tandem mass spectrometric sequencing.     

Molecular Modeling in Chromatoscopy as a New Tool in the Structure Elucidation of Novel Isomers by GC/MS

The importance of gas–solid chromatography on graphitized thermal carbon black (GTCB) as a source of additional data for the positive structural elucidation of novel isomers by gas chromatography–mass spectrometry is discussed. The retention parameters of isomers being investigated were calculated by Kiselev's method (chromatoscopy) to predict the order of their separation on a column packed with GTCB. To extend the possibilities of this method and to improve the accuracy of a prediction of retention parameters, the molecular mechanics was used for the optimization of hypothetical molecular models of isomers required for these calculations. As a test mixture 11 isomers of perhydroanthracene and perhydrophenanthrene were consedered. The predicted elution order from the column packed with GTCB of these isomers, calculated on the basis of molecular models optimized by molecular mechanics appeared to be close to the experiment, whereas the result obtained by a conventional approach appeared to fail. Molecular modeling in chromatoscopy was used for the structural elucidation of novel isomers of perhydroxanthene (PHX) and perhydro-4-thia-s-indacene (PHTI), which were found by GC–MS in reaction mixtures. The evidence for this assignment-based on the obtained GC and MS data, is discussed.