5-乙酰(苯甲酰)基-4-芳基-3,4-二氢嘧啶-2(1H)-酮的质谱裂解规律

利用飞行时间质谱仪的高分辨本领和离子阱串联质谱技术研究了5乙酰(苯甲酰)基4芳基3,4二氢嘧啶2(1H)酮(1-5)的电子轰击质谱的裂解规律.将所有质谱离子的精确质量数据经OpenLynx软件导出其分子离子和碎片离子的元素组成.根据质谱裂解规律,主要质谱离子得到了归属,并经离子阱串联质谱技术加以证实.化合物1-3的质谱出现了丰度很强的分子离子峰,其中1和3的分子离子为基峰,证明此类化合物的结构相当稳定.但4和5的分子离子峰却很弱(相对丰度在4%以下),这是由于嘧啶环4位上的苯环分别含有强吸电子基团-NO2(在苯环的间位才有此效应)和-Cl(苯环的2和4位均含有氯)所致.化合物1-5的主要裂解包括:分子离子失去芳基形成丰度很高的阳离子(M-Ar)+;分子离子失去羰基形成中等强度的阳离子(M-RCO)+;分子离子失去氢原子所产生的(M-H)+峰,以及消除中性分子NH=C=X的嘧啶环破裂裂解.此外,所有化合物在低质量区都发现明显的苯基阳离子Ph+(m/z77).并且还提出个别化合物的几个额外裂解过程为:化合物4(分子中苯环的3位上含有硝基)出现的基峰(M-OH)+;化合物5(分子中苯环的2和4位上都含有氯原子)出现了的基峰(M-Cl)+;化合物3和5分别出现了m/z238(16%)和m/z241(29%)的特征离子峰,它们由相应的离子消除中性分子四员内酰胺生成查耳酮离子,该离子具有共轭大Π键而稳定存在.     

355 nm激光作用下苯甲醚的多光子电离质谱研究

在355 nm激光作用下,利用多光子电离技术结合飞行时间质谱(TOF-MS)对苯甲醚分子进行了研究。实验结果表明苯甲醚分子的多光子电离机制属于母体分子电离-解离模型。通过对主要碎片离子的可能形成过程的讨论,得出该波长下母体分子离子解离的主要有两种通道,但是随激光能量的增强,甲基移除通道逐步占据优势成为主要通道。应用高斯软件采用HF/6-31G(d) 方法对苯甲醚分子和苯甲醚阳离子基态的几何构型进行优化得到其稳定构型,并计算了苯甲醚分子离子及其初级解离产物的能量。比较两条通道的碎片离子能量的变化,理论验证了实验中苯甲醚分子主要解离通道的合理性。     

240-250 nm波段氯苯的共振增强多光子电离研究

首次报道了在超声分子束条件下,氯苯分子(C6H5Cl)在240-250 nm紫外激发波段的共振增强多光子电离/飞行时间质谱(REMPI-TOFMS).实验获得母体离子(112C6H5Cl )和一些主要碎片离子的分质量光谱,以及它们在240.5nm和248.6nm两种激发波长下的光强指数.文中对母体离子及主要碎片离子的生成机理进行了探讨,研究表明:该波段范围内,氯苯分子首先吸收一个光子从基态1A1(S0)跃迁至激发态1B2(S1),激发态分子再吸收一个光子而电离,产生母体离子112C6H5Cl ;母体离子直接解离而生成碎片离子77C6H6 .质量更小的碎片离子51C4H3 和27C2H3 则是母体离子进一步吸收光子,然后通过快速的内转换而形成.在该波段范围内,氯苯的最佳检测波长为248.6nm.在该激发波长下,氯苯的探测限能达到到ppb量级.     

蕨素的电喷雾质谱裂解规律及紫外光谱特征

研究了蕨素类化合物电喷雾多级质谱(ESI-MSn)裂解规律,测定并归纳了其紫外光谱特征。结果表明,正离子扫描模式下,[M+H]+准分子离子首先主要发生3位和6位连氧取代基裂解失去含氧中性分子,分别形成较强的母核离子m/Z 199和201,然后进一步裂解失去中性分子或自由基,m/Z 199母核离子形成m/Z 173、171、156、143系列特征碎片离子,m/Z 201母核离子形成m/Z 183、173、168、145系列特征碎片离子。蕨素紫外光谱具有3个特征紫外吸收峰,最大吸收波长和摩尔吸光系数范围为:λmax1(290—330nm),ε1(~103L/mol.cm);λmax2(245—270nm),ε2(103—104L/mol.cm);λmax3(200—230nm),ε3(104—105L/mol.cm)。3个紫外吸收峰摩尔吸光系数比约为:ε1∶ε2∶ε3≈1∶(3—9)∶(4—20)。首次报道了蕨素的电喷雾多级质谱裂解规律及紫外光谱特征,为蕨素的快速、在线鉴别奠定了基础。     

1，3-二甲基尿嘧啶二聚体的飞行时间质谱裂解规律研究

采用不同进样方式、不同电子轰击能量和不同反应气压力测定了1,3 二甲基尿嘧啶二聚体(DMUD) 的4个立体异构体A、B、C、D的化学电离(CI)和电子轰击电离(EI)飞行时间质谱.不同方式所测得的CI谱结 果一致,4个异构体出现了强度不同的准分子离子峰(m/z=281),由此推断它们结构之间的相对稳定性次序为: B(trans syn)>D(cis syn)>A(trans anti)>C(cis anti).这一结论被低能量(25eV)电子轰击的EI谱所证实, 并且与合成产物的比例相吻合.EI谱用任何方式测谱均不出现分子离子峰(m/z=280),而出现其单体离子(m/z =140)且为基峰。给出了DMUD的飞行时间质谱裂解途径,同时对CI谱的裂解碎片进行了细致的讨论.     

二茂铁的同步辐射光电离

利用同步辐射和飞行时间质谱 ,研究了二茂铁的真空紫外光电离 ,得到了该分子的电离势为 (6 .78± 0 .0 5 )eV ,碎片离子FeC5H5+ 的出现势为 (13.4 0± 0 .10 )eV .根据实验结果 ,分析了二茂铁的主要光电离解离通道 ,估算了分子及离子的键解离能 .用密度泛涵的方法对该分子离子及一些主要的碎片离子进行了初步的量化计算 ,得到了二茂铁的电离势和一些碎片的出现势 .利用量化计算的数据还估算了分子及离子的键解离能 ,并与文献值进行了比较     

卡培他滨、5'-脱氧-5-氟胞苷和5'-脱氧-5-氟尿苷的真空紫外光电 离、光解离

利用红外激光解吸/真空紫外光电离质谱方法, 研究了核苷类抗癌药物卡培他滨及其代谢物5'-脱氧-5-氟胞苷和5'-脱氧-5-氟尿苷的光电离、光解离过程. 较低光子能量下, 可在质谱图上观察到分子离子峰及少量碎片离子, 增加光子能量使碎片离子峰大量出现. 另外对三种核苷的特征碎片, 如(M- H₂O)⁺、(Base+H)⁺、(Base+2H)⁺、(Base+30)⁺、(Base+60)⁺及戊糖离子进行了归属,并对可能的解离路径进行了讨论. 利用量子化学从头算方法研究了三种核苷可能的脱羟基过程及相应能量.     

266 nm激光作用下对溴甲苯多光子电离质谱的研究

利用266 nm激光作为光源研究了对溴甲苯分子的多光子电离解离,得到了对溴甲苯的多光子电离飞行时间质谱.实验测得了部分碎片离子占总离子信号的分支比对激光强度的依赖关系,分析了对溴甲苯分子的多光子电离解离机理,讨论了C4H+7,C6H+,C5H+5等碎片离子的可能形成过程.结果表明,碎片离子主要是经过离子离解阶梯模式产生.对实验中观测到的由激光强度变化引起的质谱峰值漂移现象作了说明.     

Photoionization and Dissociative Photoionization Study of Cholesterol by IR Laser Desorption/Tunable Synchrotron VUV Photoionization Mass Spectrometr

介绍了一种将红外激光解吸/真空紫外光电离质谱技术应用于分析胆固醇的新方法. 由于近阈值单光子电离作用,可以在低能量下只产生纯净的胆固醇分子离子峰;增加光子能量则可以使碎片离子峰大量出现. 为了验证碎片离子的归属,利用商用高分辨电子轰击电离-飞行时间质谱仪分析并指认了胆固醇主要的碎片峰. 此外,采用量子化学从头算的方法研究了胆固醇母体离子和碎片构型,并讨论了部分主要的光解离机理     

1,3-和1,4-环己亚硝酸二酯电子轰击解离的结构效应（英文）

烷基亚硝酸二酯是一种重要的亚硝化剂,也是大气中NOx污染物的来源之一,近年来引起了人们的广泛关注.烷基亚硝酸二酯中两个ONO官能团对分子反应活性的影响以及在化学反应中的作用尚不清楚.本文用电子碰撞电离质谱研究了 1,3-环己亚硝酸二酯和1,4-环己亚硝酸二酯的解离过程.实验结果发现两种结构异构体的分解产物不同:除了亚硝酸酯的特征碎片NO~+(m/z=30)外,对于1,3-异构体,碎片离子m/z=43和71的丰度最高;而对于1,4-异构体,电子碰撞电离质谱谱图中解离产物m/z=29、57、85和97的强度较大.对中性分子、分子离子以及中间产物的结构和电荷计算结果显示,1,3-环己亚硝酸二酯的分解清楚地显示出两步解离机制,即母体阳离子M~+首先失去一个NO,然后中间离子(M-NO)~+通过两个αC-βC键的断裂打开六元碳环;对于1,4-环己亚硝酸二酯,除了两步分解机制之外,还可以直接从母体阳离子M~+发生βC-βC键的裂解.研究结果有助于理解在大气反应及亚硝化合成反应中烷基亚硝酸二酯的分子结构对反应历程的影响.     

13-乙酰基-9-甲基-11-羰基-8-氧代-10,12-二氮杂三环[7.3.1.02,7]十三碳-2,4,6-三烯的一锅煮合成和结构表征

描述了一种有效的环境友好的“一锅煮”法合成13-乙酰基-9-甲基-11-羰基-8-氧代-10,12-二氮杂三环[7．3．1．0~(2,7)]十三碳-2,4,6-三烯。该法用廉价易得的溴化镁作催化剂,在无溶剂存在下,由起始原料水杨酸,乙酰丙酮和脲通过Biginelli缩合反应伴随着分子内的Michael加成反应一步完成。用核磁共振氢谱、碳谱、飞行时间质谱以及红外光谱数据表征了产物的结构为一氧桥多环化合物,而不是带有自由羟基的二氢嘧啶酮。最后由质谱给出的精确质量及其所代表的元素组成推出了该化合物的质谱裂解途径。     

Unimolecular dissociation of singly- and multiply-charged fullerene ions

The formation of fragment ions from C₆₀ due to electron impact ionization leading to a bimodal fragmentation pattern with a minimum around the cluster size of 30 is investigated with help of mass spectrometric techniques. Based on a detailed analysis of the energetics and kinetics of the singly- and multiply-charged fragment ions by two-sector field mass spectrometry (MIKE-scans) we can conclude that on the one hand some of the dissociation reactions proceed via evaporation of an intact C₆ ⁺ or C₄ ⁺ unit (and not via the sequential loss of smaller molecular carbon units). On the other hand, measured appearance energies and the direct observation of sequential C₂-loss reactions confirm that the sequential loss of neutral C₂ units is the dominant production mechanism for C_n ^z+ fragment ions with sizes 40 < n < 60. This revised version was published online in August 2006 with corrections to the Cover Date.     

乙胺分子的多光子电离过程质谱研究

报道了乙胺分子在４４０～４７５ｎｍ波长范围内多光子电离（ＭＰＩ）质谱（ＭＳ）研究结果。碎片离子主要由母体离子碎裂模式产生。母体离子ＣＨ３ＣＨ２Ｎ＋·Ｈ２由经３ｓ里德堡态的（２＋２）共振多光子电离产生后，大部分发生β键断裂，形成ＣＨ２＝Ｎ＋Ｈ２离子，还有一部分再吸收一个光子，通过Ｃ－Ｈ（ＣＨ２）键的断裂产生了ＣＨ３ＣＨ＝Ｎ＋Ｈ２离子。ＣＨ３ＣＨ＝Ｎ＋Ｈ２和ＣＨ２＝Ｎ＋Ｈ２离子最容易发生的碎裂过程是脱去氢分子，分别产生Ｃ２Ｈ４Ｎ＋（分子式）离子和ＣＨ≡Ｎ＋Ｈ离子。     

Ionic Angular Distributions Induced by Strong-Field Ionization of Tri-Atomic Molecules

Angular distributions of fragment ions from ionization of several tri-atomic molecules(CO_2, OCS, N_2O and NO_2) by strong 800-nm laser fields are investigated via a time-of-flight mass spectrometer. Anisotropic angular distributions of fragment ions, especially those of atomic ions, are observed for all of the molecules studied.These anisotropic angular distributions are mainly due to the geometric alignment of molecules in the strong field ionization. Distinct different patterns in ionic angular distributions for different molecules are observed. It is indicated that both molecular geometric structure and ionization channels have effects on the angular distributions of strong field ionization/fragmentation.     

在超声分子束下气相四甲基硅分子的多光子解离与电离

采用超声分子束技术，以飞行时间质谱仪，在４１０～３７１ｎｍ内着重检测了不同波长、不同能量的激光对气相Ｓｉ（ＣＨ３）４分子多光子电离（ＭＰＩ）飞行时间（ＴＯＦ）质谱产物分布的影响。根据实验结果，对Ｓｉ（ＣＨ３）４分子多光子解离电离可能经历的通道和反应机理进行了讨论。     

Fragmentation of oxime and silyl oxime ether odd-electron positive ions by the McLafferty rearrangement: new insights on structural factors that promote α,β fragmentation

The McLafferty rearrangement is an extensively studied fragmentation reaction for the odd-electron positive ions from a diverse range of functional groups and molecules. Here, we present experimental and theoretical results of 12 model compounds that were synthesized and investigated by GC-TOF MS and density functional theory calculations. These compounds consisted of three main groups: carbonyls, oximes and silyl oxime ethers. In all electron ionization mass spectra, the fragment ions that could be attributed to the occurrence of a McLafferty rearrangement were observed. For t-butyldimethylsilyl oxime ethers with oxygen in a β-position, the McLafferty rearrangement was accompanied by loss of the t-butyl radical. The various mass spectra showed that the McLafferty rearrangement is relatively enhanced compared with other primary fragmentation reactions by the following factors: oxime versus carbonyl, oxygen versus methylene at the β-position and ketone versus aldehyde. Calculations predict that the stepwise mechanism is favored over the concerted mechanism for all but one compound. For carbonyl compounds, C-C bond breaking was the rate-determining step. However, for both the oximes and t-butyldimethylsilyl oxime ethers with oxygen at the β-position, the hydrogen transfer step was rate limiting, whereas with a CH(2) group at the β-position, the C-C bond breaking was again rate determining. n-Propoxy-acetaldehyde, bearing an oxygen atom at the β-position, is the only case that was predicted to proceed through a concerted mechanism. The synthesized oximes exist as both the (E)- and (Z)-isomers, and these were separable by GC. In the mass spectra of the two isomers, fragment ions that were generated by the McLafferty rearrangement were observed. Finally, fragment ions corresponding to the McLafferty reverse charge rearrangement were observed for all compounds at varying relative ion intensities compared with the conventional McLafferty rearrangement.     

Identification of new flavan-3-ol monoglycosides by UHPLC-ESI-Q-TOF in grapes and wine

Flavan-3-ol monoglycosides, having four aglycons (+)-catechin, (-)-epicatechin, (-)-epigallocatechin and epicatechin gallate monomeric units, are detected for the first time in Vitis vinifera L. cv. Merlot grape seeds and wine. These compounds were analyzed in red wine, seed and skin extracts by electrospray ionization quadrupole time of flight mass spectrometry (MS) in negative mode. Fragment ions derived from retro-Diels Alder, heterocyclic ring fragmentation, benzofuran forming fragmentation and glycoside fragmentations were detected in targeted MS/MS mode. These compounds were not detected in skins; the comparative study showed evidence that these glycosylated compounds originate only from grape seeds. Our method allows for the identification of these glycosylated compounds based on their exact mass and their specific fragmentation pattern. However, exact glucose position on the monomeric units can not be determined. This work allowed us to partially identify 14 new flavan-3-ol monoglycosides, based on the exact mass of the molecular ions and their specific retro-Diels Alder, heterocyclic ring fragmentation, benzofuran forming fragmentation and glycoside fragmentations.     

Differentiation of aminomethyl corrole isomers by mass spectrometry

Two new isomeric aminomethyl corrole derivatives of [5,10,15-tris(pentafluorophenyl)corrolato]gallium(III) were synthesized with pyridine (py) molecules as axial ligands. When investigated by electrospray ionization mass spectrometry, in the positive and the negative ion modes, these compounds showed an unusual gas-phase behavior that could be used for their differentiation. In the positive ion mode, the differentiation was achieved through the formation of diagnostic fragment ions formed from [M-py?+?H](+) precursors, by (CH(3) )(2) NH and HF losses. An unusual addition of water to the main fragment ions provides an alternative route for isomer identification. Semi-empirical calculations were performed to elucidate the structures and stabilities of the main ionic species formed in the positive ion mode. In the negative ion mode isomer discrimination is accomplished via the fragmentation of the methoxide adduct ions [M-py?+?CH(3) O](-) through (CH(3) )(2) N(.) and HF losses.     

Electrospray ionization multiple-stage tandem mass spectrometric analysis of diglycosyldiacylglycerol glycolipids from the bacteria Bacillus pumilus

Electrospray ionization (ESI) combined with multiple-stage tandem mass spectrometry (MS(n)) was used to directly analyze the glycolipid mixture from bacteria Bacillus pumilus without preliminary separation. Full scan ESI-MS revealed the composition of picomole quantities of glycerolglycolipid species containing C(14)-C(19) fatty acids, some of which were monounsaturated. Two main components were identified from their molecular masses and fragmentation pathways. The fragmentation pathway of the known compound compared with the investigated compound verified the proposed structure as 1(3)-acyl-2-pentadecanoyl-3(1)-O-[beta-D-glucopyranosyl-(1-->6)-O-beta-D-glucopyranosyl]-sn-glycerols. A comparison of the multiple tandem mass spectra of the different alkali-metal cation adducts indicates that the intensity of fragments and the dissociation pathways are dependent on the alkali-metal type. The basic structures of glycerolglycolipids were reflected clearly from the fragmentation patterns of the sodium cations. The intense fragments of the sugar residue from the precursor ions were obtained from the lithiated adduct ions. ESI-MS(n) spectra of [M + K](+) ions did not provide as much fragmentation as [M + Na](+) and [M + Li](+) adducts, but their spectra allow the position of glycerol acylation to be determined. On the basis of MS(2) spectra of [M + K](+) ions, it was established that all components have a C(15:0) fatty acid at the sn-2 position of the glycerol backbone and C(14)-C(19) acids at the sn-1 position of the glycerol backbone. Copyright 1999 John Wiley & Sons, Ltd.