Sequencing of Oligourea Foldamers by Tandem Mass Spectrometry

This study is focused on sequence analysis of peptidomimetic helical oligoureas by means of tandem mass spectrometry, to build a basis for de novo sequencing for future high-throughput combinatorial library screening of oligourea foldamers. After the evaluation of MS/MS spectra obtained for model compounds with either MALDI or ESI sources, we found that the MALDI-TOF-TOF instrument gave more satisfactory results. MS/MS spectra of oligoureas generated by decay of singly charged precursor ions show major ion series corresponding to fragmentation across both CO-NH and N′H-CO urea bonds. Oligourea backbones fragment to produce a pattern of a, x, b, and y type fragment ions. De novo decoding of spectral information is facilitated by the occurrence of low mass reporter ions, representative of constitutive monomers, in an analogous manner to the use of immonium ions for peptide sequencing.      

Identification of Vitamin D3 Oxidation Products Using High-Resolution and Tandem Mass Spectrometry

In a successful fortification program, the stability of micronutrients added to the food is one of the most important factors. The added vitamin D3 is known to sometimes decline during storage of fortified milks, and oxidation through fatty acid lipoxidation could be suspected as the likely cause. Identification of vitamin D3 oxidation products (VDOPs) in natural foods is a challenge due to the low amount of their contents and their possible transformation to other compounds during analysis. The main objective of this study was to find a method to extract VDOPs in simulated whole milk powder and to identify these products using LTQ-ion trap, Q-Exactive Orbitrap and triple quadrupole mass spectrometry. The multistage mass spectrometry (MSⁿ) spectra can help to propose plausible schemes for unknown compounds and their fragmentations. With the growth of combinatorial libraries, mass spectrometry (MS) has become an important analytical technique because of its speed of analysis, sensitivity, and accuracy. This study was focused on identifying the fragmentation rules for some VDOPs by incorporating MS data with in silico calculated MS fragmentation pathways. Diels–Alder derivatization was used to enhance the sensitivity and selectivity for the VDOPs’ identification. Finally, the confirmed PTAD-derivatized target compounds were separated and analyzed using ESI(+)-UHPLC-MS/MS in multiple reaction monitoring (MRM) mode.

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Sequencing Lys-N Proteolytic Peptides by ESI and MALDI Tandem Mass Spectrometry

In this study, we explored the MS/MS behavior of various synthetic peptides that possess a lysine residue at the N-terminal position. These peptides were designed to mimic peptides produced upon proteolysis by the Lys-N enzyme, a metalloendopeptidase issued from a Japanese fungus Grifola frondosa that was recently investigated in proteomic studies as an alternative to trypsin digestion, as a specific cleavage at the amide X-Lys chain is obtained that provides N-terminal lysine peptide fragments. In contrast to tryptic peptides exhibiting a lysine or arginine residue solely at the C-terminal position, and are thus devoid of such basic amino acids within the sequence, these Lys-N proteolytic peptides can contain the highly basic arginine residue anywhere within the peptide chain. The fragmentation patterns of such sequences with the ESI-QqTOF and MALDI-TOF/TOF mass spectrometers commonly used in proteomic bottom-up experiments were investigated.     

Gangliosidome of a Human Hippocampus in Temporal Lobe Epilepsy Resolved by High-Resolution Tandem Mass Spectrometry

In this study, we developed a high-resolution tandem mass spectrometry (HR MS) approach to assess presumed changes in gangliosidome of a human hippocampus affected by temporal lobe epilepsy (TLE) in comparison with a normal hippocampus. Gangliosides, membrane glycolipids, are particularly diverse and abundant in the human brain, and participate in ion transport and modulation of neuronal excitability. Changes in structural ganglioside pattern potentially linked to TLE molecular pathogenesis have not been explored in detail. Aiming to characterize TLE-specific gangliosidome, we analyzed the native gangliosides purified from a human hippocampal tissue sample affected by TLE and a control hippocampus using HR MS. Marked differences of ganglioside expression were shown in TLE vs. control, particularly with respect to the sialylation degree of components, discovered as a characteristic feature of TLE. Another major finding is the occurrence of tetrasialofucogangliosides in TLE and species modified by either O-acetylation or CH₃COO⁻. Structural analysis by higher-energy collisional dissociation (HCD) MS/MS gave rise to fragmentation patterns implying that the GQ1b (d18:1/18:0) isomer is specifically associated with TLE. Further investigation in a larger sample is needed in order to confirm the discovery of ganglioside structures specifically expressed in human TLE and to provide information on the probable role of gangliosides in the molecular events underlying seizures.     

Similarity of High-Resolution Tandem Mass Spectrometry Spectra of Structurally Related Micropollutants and Transformation Products

High-resolution tandem mass spectrometry (HRMS2) with electrospray ionization is frequently applied to study polar organic molecules such as micropollutants. Fragmentation provides structural information to confirm structures of known compounds or propose structures of unknown compounds. Similarity of HRMS2 spectra between structurally related compounds has been suggested to facilitate identification of unknown compounds. To test this hypothesis, the similarity of reference standard HRMS2 spectra was calculated for 243 pairs of micropollutants and their structurally related transformation products (TPs); for comparison, spectral similarity was also calculated for 219 pairs of unrelated compounds. Spectra were measured on Orbitrap and QTOF mass spectrometers and similarity was calculated with the dot product. The influence of different factors on spectral similarity [e.g., normalized collision energy (NCE), merging fragments from all NCEs, and shifting fragments by the mass difference of the pair] was considered. Spectral similarity increased at higher NCEs and highest similarity scores for related pairs were obtained with merged spectra including measured fragments and shifted fragments. Removal of the monoisotopic peak was critical to reduce false positives. Using a spectral similarity score threshold of 0.52, 40% of related pairs and 0% of unrelated pairs were above this value. Structural similarity was estimated with the Tanimoto coefficient and pairs with higher structural similarity generally had higher spectral similarity. Pairs where one or both compounds contained heteroatoms such as sulfur often resulted in dissimilar spectra. This work demonstrates that HRMS2 spectral similarity may indicate structural similarity and that spectral similarity can be used in the future to screen complex samples for related compounds such as micropollutants and TPs, assisting in the prioritization of non-target compounds.

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新化合物五氧化铀的电喷雾串联质谱法制备与表征

采用醋酸铀酰为原料在气相中制备了HOUO2OH负离子, 在一定条件下再与O2反应, 从而制备了UO5负离子, 并采用串联质谱法对UO5进行了表征, 考察了生成条件对制备UO5负离子的影响. 初步实验表明在不同能量作用下UO5负离子能释放出O2. 探讨了气相中负离子与分子反应生成UO5负离子的可能机理, 指出通过调控分子与离子的碰撞时间和碰撞能量可以控制离子的电子活动半径, 合适的能量可使电子云的半径落在rinert≤rReactiverreactive≤rdecomposition之间, 从而促进某些化学反应的进行, 以合成某些通常状况下难以生成的物质.     

Structural Characterization of Anticancer Drug Paclitaxel and Its Metabolites Using Ion Mobility Mass Spectrometry and Tandem Mass Spectrometry

Paclitaxel (PTX) is a popular anticancer drug used in the treatment of various types of cancers. PTX is metabolized in the human liver by cytochrome P450 to two structural isomers, 3′-p-hydroxypaclitaxel (3p-OHP) and 6α-hydroxypaclitaxel (6α-OHP). Analyzing PTX and its two metabolites, 3p-OHP and 6α-OHP, is crucial for understanding general pharmacokinetics, drug activity, and drug resistance. In this study, electrospray ionization ion mobility mass spectrometry (ESI-IM-MS) and collision induced dissociation (CID) are utilized for the identification and characterization of PTX and its metabolites. Ion mobility distributions of 3p-OHP and 6α-OHP indicate that hydroxylation of PTX at different sites yields distinct gas phase structures. Addition of monovalent alkali metal and silver metal cations enhances the distinct dissociation patterns of these structural isomers. The differences observed in the CID patterns of metalated PTX and its two metabolites are investigated further by evaluating their gas-phase structures. Density functional theory calculations suggest that the observed structural changes and dissociation pathways are the result of the interactions between the metal cation and the hydroxyl substituents in PTX metabolites.

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串联质谱法鉴定丙基膦酸烷基酯异构体

采用串联质谱(MS/MS)研究了丙基膦酸烷基酯异构体,以鉴定与磷相连的丙基基团。针对电子轰击质谱(EI-MS)谱图中特征离子m/z 125和化学电离质谱(CI-MS)谱图中的准分子离子,进行串联质谱研究,对碰撞气压力和碰撞能量进行优化。实验结果表明:在碰撞能量20 V,碰撞气压力1.0 mTorr时,电子轰击串联质谱(EI-MS/MS)模式下,正丙基膦酸酯的母离子m/z 125碎裂产生较强的子离子m/z 107,而异丙基膦酸酯的母离子m/z 125则碎裂产生较强的子离子m/z 65和83;在化学电离串联质谱(CI-MS/MS)模式下,正丙基膦酸酯的准分子离子产生子离子m/z 125(基峰)和107,异丙基膦酸酯的准分子离子产生子离子m/z 125、107和83;通过串联质谱反应,能清晰地区分正丙基和异丙基膦酸烷基酯(C≥2)。     

Determination of Chloramphenicol in Milk Using a QuEChERS-Based on Liquid Chromatography Tandem Mass Spectrometry Method

A quantitative method for the determination of chloramphenicol in milk samples was developed based on the QuEChERS (quick, easy, cheap, effective, rugged, and safe) approach for liquid chromatography–tandem mass spectrometry (LC–MS/MS). Homogenized milk samples were extracted with acetonitrile. The partitioning step was performed after the addition of magnesium sulfate and sodium chloride. Chloramphenicol was determined using the electrospray negative ionization mode with tandem mass spectrometry. The procedure was validated according to the requirements of Commission Decision 2002/657/EC. The apparent recovery ranged from 90% to 110% and within-laboratory reproducibility was lower than 12%. The calculated limit of decision was 0.10 μg kg^?1 and the detection capability was 0.15 μg kg^?1. Validation results demonstrated that this method fulfills criteria for the determination of chloramphenicol in milk.     

合成多肽的电喷雾质谱研究

利用电喷雾多极串联质谱对3种合成多肽进行了系统的鉴定和分析研究。首先通过全扫描模式测定了其分子量，然后选择[M H]^ 或[M 2H]^2 离子通过串联质谱(MS／MS)得到碎片离子，采用y离子和b离子互补的方法测定了多肽序列。利用文献数据对这种方法进行了验证，实验结果表明，该方法简便、快速、实用。     

High-Resolution Tandem Mass Spectrometry Identifies a Particular Ganglioside Pattern in Early Diabetic Kidney Disease of Type 2 Diabetes Mellitus Patients

Considering the valuable information provided by glycosphingolipids as molecular markers and the limited data available for their detection and characterization in patients suffering from Type 2 diabetic kidney disease (DKD), we developed and implemented a superior method based on high-resolution (HR) mass spectrometry (MS) and tandem MS (MS/MS) for the determination of gangliosides in the urine of DKD patients. This study was focused on: (i) testing of the HR MS and MS/MS feasibility and performances in mapping and sequencing of renal gangliosides in Type 2 DM patients; (ii) determination of the changes in the urine gangliosidome of DKD patients in different stages of the disease—normo-, micro-, and macroalbuminuria—in a comparative assay with healthy controls. Due to the high resolution and mass accuracy, the comparative MS screening revealed that the sialylation status of the ganglioside components; their modification by O-acetyl, CH₃COO⁻, O-fucosyl, and O-GalNAc; as well as the composition of the ceramide represent possible markers for early DKD detection, the assessment of disease progression, and follow-up treatment. Moreover, structural investigation by MS/MS demonstrated that GQ1d(d18:1/18:0), GT1α(d18:1/18:0) and GT1b(d18:1/18:0) isomers are associated with macroalbuminuria, meriting further investigation in relation to their role in DKD.     

Identification and Structural Assessment of Alkaline-Earth Metal Complexes with Flavonols by FAB Mass Spectrometry

Complexation of a series of flavonols with Mg^{2 +}, Ca^{2 +}, and Ba^{2 +} ions was studied by FAB mass spectrometry. The mass spectra of flavonol solutions containing magnesium ions revealed formation of 1 : 2 complexes MgL₂, undetectable by spectrophotometric and spectrofluorimetric methods. Experiments with a crown-substituted flavonol revealed formation of not unly previously known chelate complexes MgL and Mg₂L, but also of the 1 : 2 complex MgL₂ and crown complex MgHL. The barium ions form with the crown-substituted flavonol two types of sandwich complexes: Ba(HL)₂ and Ba₂(HL)₂. With the Ca^{2 +} ions, such complexes are not formed, and only the fragmentation product of the complex Ca(HL)₂ was detected.     

槲皮素和芦丁的某些金属配合物的电喷雾质谱研究

槲皮素(quercetin)和芦丁(rutin)都是天然的黄酮类化合物,且槲皮素是芦丁的甙元,它们广泛存在于许多植物的花、叶、果实中,对其药理作用研究较多[1-3],但由于槲皮素和芦丁不溶于或难溶于水,不利于吸收[4],极大地限制了其生物利用度和体内给药途径.     

An Alternative Strategy for Screening and Confirmation of 330 Pesticides in Ground- and Surface Water Using Liquid Chromatography Tandem Mass Spectrometry

The presence of pesticide residues in water is a huge worldwide concern. In this paper we described the development and validation of a new liquid chromatography tandem mass spectrometric (LC-MS/MS) method for both screening and quantification of pesticides in water samples. In the sample preparation stage, the samples were buffered to pH 7.0 and pre-concentrated on polymeric-based cartridges via solid-phase extraction (SPE). Highly sensitive detection was carried out with mobile phases containing only 5 mM ammonium formate (pH of 6.8) as an eluent additive and using only positive ionization mode in MS/MS instrument. Hence, only 200-fold sample enrichment was required to set a screening detection limit (SDL) and reporting limit (RL) of 10 ng/L. The confirmatory method was validated at 10 and 100 ng/L spiking levels. The apparent recoveries obtained from the matrix-matched calibration (5–500 ng/L) were within the acceptable range (60–120%), also the precision (relative standard deviation, RSD) was not higher than 20%. During the development, 480 pesticides were tested and 330 compounds fulfilled the requirements of validation. The method was successfully applied to proficiency test samples to evaluate its accuracy. Moreover, the method robustness test was carried out using higher sample volume (500 mL) followed by automated SPE enrichment. Finally, the method was used to analyze 20 real samples, in which some compounds were detected around 10 ng/L, but never exceeded the assay maximum level.     

衍生化电喷雾串联质谱法快速检测甲基丙二酸尿症

甲基丙二酸尿症的主要标志物为甲基丙二酸.采用正丁醇衍生化,以结合同位素化合物为内标,用电喷雾串联质谱快速、准确且选择性地定量检测了尿液中的甲基丙二酸.同时定量检测了病人治疗过程中尿液的肌酐,应用甲基丙二酸与肌酐的比值对两例甲基丙二酸病人的治疗过程予以监控.所建立的定量方法具有快速、准确和高选择性等特点,既可用于大规模和高通量的筛查(2min/样),又可用于病人治疗过程中的监控.     

Identification of Phlorotannins in the Brown Algae,Saccharina latissima and Ascophyllum nodosum by Ultra-High-Performance Liquid Chromatography Coupled to High-Resolution Tandem Mass Spectrometry

Phlorotannins are bioactive polyphenols in brown macroalgae that make these algae interesting as healthy food. Specific phlorotannins are, however, seldom identified, and extracts from different species are often only analysed for total phenolic content (TPC). In this study, our focus was to identify phlorotannin molecules from Saccharina latissima and Ascophyllum nodosum (a species rich in these compounds) using ultra-high-performance liquid chromatography coupled to high-resolution tandem mass spectrometry (UHPLC-HRMS²). Water and ethanol (30 and 80% v/v) were used at solid:liquid ratios, extraction times and temperatures, proposed to result in high TPC in extracts from other species. The S. latissima extracts, however, did not allow phlorotannin detection by either UHPLC-UV/Vis or UHPLC-HRMS², despite a TPC response by the Folin–Ciocalteu assay, pinpointing a problem with interference by non-phenolic compounds. Purification by solid phase extraction (SPE) led to purer, more concentrated fractions and identification of four phlorotannin species in A. nodosum and one in S. latissima by UHPLC-HRMS², using extracts in ethanol 80% v/v at a solid:liquid ratio of 1:10 for 20 h at 25 °C with an added 10 h at 65 °C incubation of remaining solids. The phlorotannin with the formula C₁₂H₁₀O₇ (corresponding to bifuhalol) is the first identified in S. latissima.     

Understanding the Fragmentation Pathways of Carbocyclic Derivatives of Amino Acids by Using Electrospray Ionization Tandem Mass Spectrometry

Aminoacyl derivatives of aminoadamantanes amantadine and rimantadine have been investigated in regard to their antiviral properties. So far, few studies on the mass spectrometric fragmentation pathway of these compounds have been reported using high-resolution mass spectrometry (HRMS). Two major fragmentation pathways have been observed. For the rimantadine derivatives, losses of rimantadine and N-(1-adamantyl) ethylformamide were described. Similarly, in case of amantadine derivatives, there were losses of amantadine and N-(1-adamantyl) formamide. The loss of the aminoacyl group was common to all of the studied compounds. Understanding the fragmentation mechanism can bring new insight into the characterization of these compounds.     

血清肌钙蛋白Ⅰ液相色谱串联质谱法建立及优化

建立并优化了液相色谱串联质谱法定量血清肌钙蛋白I.免疫磁珠富集血清肌钙蛋白I,经变性、还原、乙酰化、胰酶消化、固相萃取纯化,采用SymmetryShieldC18柱分离,以含0.1%甲酸水溶液和含0.1%的甲酸乙腈溶液为流动相,梯度分离目标肽段,流速0.2 mL/min,温度35℃;使用电喷雾正离子模式扫描,在多反应监测模式下进行测定,目标肽段出峰时间约为4.95 min;方法的最低检测限为2.5 ng/mL,定量限为8.32 ng/mL,在（10~600）ng/mL范围内线性良好,相关系数为0.99;标准物质SRM2921偏倚为-7.94%~-6.49%;低、中、高样本总不精密度分别为6.43%、3.18%和2.75%;携带污染率为-0.47%~0.04%.本方法选择性高、重复性和准确度好、携带污染小,为进一步研究血清cTnI参考方法建立提供依据.     

高效液相色谱-电喷雾串联质谱法测定蔬菜中虫酰肼和甲氧虫酰肼残留

建立了蔬菜中虫酰肼和甲氧虫酰肼的高效液相色谱-电喷雾串联质谱(LC-ESI-MS/MS)检测方法。样品经碱性乙腈提取,固相萃取净化,反相高效液相色谱柱分离后进行质谱分析。在选择反应监测模式(SRM)下进行特征母-子离子对信号采集。分别以碎片离子m/z297和m/z149进行外标法定量。虫酰肼和甲氧虫酰肼残留的检出限(S/N=3)为1.0μg/kg,加标回收测得定量限为4.0μg/kg;在5.0～200μg/L时峰强度与质量浓度的线性关系良好(r2>0.996)。在4.0、10.0和20.0μg/kg3个添加水平,通过基质曲线校正后,虫酰肼和甲氧虫酰肼的平均回收率范围为90%～110%和70%～80%;相对标准偏差小于8%。结果表明,该法简单、灵敏,适用于蔬菜中虫酰肼和甲氧虫酰肼残留的分析确证。     

离子色谱-质谱联用测定牛奶中的高氯酸盐、溴酸盐和碘离子

以离子色谱-质谱联用同时测定了不同品牌牛奶中的高氯酸盐、溴酸盐和碘离子。以高容量、强亲水性IonPac AS20(2 mm)为分析柱,EGC在线产生KOH为淋洗液,串联质谱检测。ESIMS/MS以多元反应监测(MRM)模式分别监控高氯酸盐的m/z100.8/84.9、98.8/82.9离子对,溴酸盐的m/z126.8/110.9、126.8/95.0离子对和碘离子的m/z126.8/127.0离子对,并分别对高氯酸盐、溴酸盐和碘离子以m/z98.8/82.9、126.8/110.9和126.8/127.0离子对的峰面积进行定量。该方法对高氯酸盐、溴酸盐和碘离子的检出限(S/N=3)分别为0.02、0.1和0.5μg/L,线性相关系数分别是0.999(0.05~50μg/L)、0.999(0.5~100μg/L)、0.998(1~1 000μg/L)。高氯酸盐和碘离子的样品加标回收率分别在102%~108%之间和86%~114%之间。