有机磷化合物的质谱研究(Ⅶ)——二氮二磷杂环戊烷衍生物的化学电离质谱

本文报道了七种4.5-二氧代-2-硫代-1,3,2,4-二氮二磷杂环戊烷衍生物的化学电离质谱(CIMS,甲烷为反应气),结果表明:CIMS中准分子离子MH~+为基峰离子;MH~+离子易发生失去H_2S,CO,C_3H_6等小分子的裂解,(M+C_2H_5)~+离子存在再断裂。     

缩氨基脲类和缩氨基硫脲类衍生物的质谱研究

用高、低分辨质谱,重氢标记和亚稳跃迁研究了代缩氨脲和缩氨基硫脲类衍生物的质谱碎行为。结果表明,分子离子的丰度、基峰离子的生成方式以及碎非离子的种类、丰度和数量主要取于取代基R的诱导效应和共轭效应的综合影响。质谱的碎裂特征是:(1)当R为N(CH2)2,OH分子的电子云分布均匀,共轭性好,基峰为分子离子峰。(2)当R为H,F时缩氨基脲8-N位缺子最甚,导致9-N和10-C之间键的断裂,生成的高稳定离子ρ-RC6H4CH=N[+]=NH为墓峰。缩氨基硫脲类衍生物,因电子云分布均匀,基峰仍为分子离子峰。(3)当R为Br,NO2时,由于诱效应强烈,分子的电子云分布不均匀,12-O(或12-S)成为缺电子最甚的原子,8-N和9-N之间键裂、重排而生成的离子-HNC(NH2)=XH]:(X=O,S)为基峰。(4)H-NH2基团重排到苯环5位上,生成离子(O-RC6H4NH2).+[1]。只有当R为H时,反应最易反生。R为强电子基或强极电基,对反应都不利。     

杂氮硅三环成环反应的研究

本文报导了与硅原子直接相连的有机基团(R)对杂氮硅三环成环速率的影响。利用气相色谱检测成环反应的产物之一——乙醇的生成速率和数量,并同与硅相连的R基团对成环反应速率的影响作比较。实验结果表明五种杂氮硅三环成环速度顺序为Cl_2CH—>ClCH_2—>ClCH_2CH_2CH_2—>CH_2=CH—>CH_3—,这与理论推断相符。     

盖帽三核钴羰基簇合物(μ_3-CH_3C)Co_3(CO)_7(μ-PPh_2CH_2PPh_2)和(μ_3-CH_3C)Co_3(CO)_9的质谱研究

本文从结构化学角度,阐述了标题化合物的EI质谱断裂行为。这些化合物的分子离子基本上按分步断裂分别失去羰基,直至获得[CH_3CCo_3(PPh_2CH_2PPh_2)]~+和[CH_3CCo_3]~+。然后,这些残基和含膦配体继续断裂,失去Ph、PhP、Ph_3P、C_7H_7、C_6H_6、C_2H_2、H_2和Co等,生成各种相应的三核、二核和单核钴的碎片离子。     

二甲基(五氟苯基)硅烷衍生物的质谱重排反应

利用气相色谱质谱联用仪在电子轰击离子源下对20个二甲基(五氟苯基)硅烷衍生物进行分析,发现大部分化合物质谱图上无分子离子峰,少数化合物可观察到较弱的分子离子峰。所有化合物质谱图上都具有较强的[M-CH3]+离子,且在个别化合物的谱图上表现为基峰,该离子来自游离基中心诱导发生的α(C-Si键断裂)裂解。各化合物的谱图上均具有m/z 77和m/z 79的特征离子,在绝大多数化合物的谱图上表现为基峰。对离子进行归属时发现该类离子并不能通过化合物分子内键的直接裂解而得到,推测该类离子是通过进行分子内的骨架重排反应而得到的三配位硅正离子,推断其生成途径为单分子亲核取代反应历程(SN1)。进一步对不含氟的二甲基(苯基)硅烷衍生物进行分析,未检出该类重排特征离子,从而印证了对于二甲基(五氟苯基)硅烷衍生物中重排离子生成途径的推测。     

三唑仑苯二氮(艹卓)类药物的电喷雾质谱裂解特征

采用电喷雾/四极杆飞行时间质谱(ESI-QqTOF)联用技术,对3种三唑仑苯二氮(艹卓)类药物进行CID研究,并以质子化准分子离子[M+H]+作为内标物,对碎片离子进行了准确质量测定,确认了这些碎片离子的元素组成,探讨了该类化合物的质谱裂解规律.研究发现,它们的ESI-MS2(源内)和ESI-MS3质谱分别生成脱去N2分子、HCN或CH3CN分子和Cl原子的碎片离子,其中m/z 205为3种药物共有的碎片离子,这些特征可用于三唑仑苯二氮(艹卓)类药物的体内代谢转化和定量研究.     

基于密度泛函理论的橘霉素衍生物质谱裂解行为研究

采用电喷雾离子阱质谱(ESI-IT-MSn),研究了橘霉素衍生物正离子模式下的裂解行为,并结合密度泛函理论(DFT)证明裂解途径的可靠性,为同类化合物的准确鉴定提供实验和理论基础。核磁共振仪对海莲内生真菌代谢产物分离得到的橘霉素衍生物结构进行确认,电喷雾离子阱质谱正离子模式扫描,测定化合物氢氘交换产物多级裂解质谱图,并结合键断裂能和Mulliken电荷分布,进一步验证裂解规律。实验结果表明,分子结构中-COOH和CH3COO-在一级裂解过程中易脱除CO2和COCH2,CID-MS2观测到丢失H2O/HDO、H2O和-CH3或CHCO/CDCO的碎片离子峰,且丰度依次降低,理论计算也证明,这些碎片离子的总能量依次增大,稳定性降低,键断裂能逐渐增大。该结果丰富了橘霉素衍生物的电喷雾质谱裂解规律,有助于橘霉素衍生物结构的准确鉴定,为该类化合物的检测和痕量分析提供了更多支持。     

2-乙酰氨基-3-苯基-N-苯基-丙烯酰胺衍生物的电子轰击质谱研究

本文报道了6种新的丙烯酰胺衍生物的EI谱。在精确质量测量和B/E,B~2/E联动扫描亚稳离子测定的基础上,着重讨论了该类化合物的共同质谱特征:如分子离子失去H_2O的成环反应;产物离子的开环反应;分子内的氢重排反应等。同时,利用Hammett方程讨论了化合物中N-苯基端苯环上不同取代基对特定碎片离子强度的影响     

有机磷化合物的质谱研究(Ⅳ)——1,3,2-二氮磷杂环戊烷衍生物的电子轰击(EI)质谱

本文报道了9种新的含磷杂环化合物的电子轰击(EI)质谱。根据B/E,B~2/E联动扫描的亚稳离子测定和高分辨精确质量测量数据,着重讨论了该类化合物的基峰离子形成过程和分子内的几种重排反应;同时探讨了该类化合物的一般裂解机理和质谱特征。     

N-环己基吡嗪酮类化合物的EI质谱及其解析

总结和归属了 (2H)_2_环己基_3 ,4二氢吡咯并[1 ,2_a]吡嗪_1_酮及其7个苯甲酰基衍生物和3个苯乙酰基衍生物在电子轰击电离质谱 (EI_MS)中的主要裂解方式和特征 ,指明了主要碎片离子的来源和结构 ,这10个芳酰基衍生物质谱图中的主要碎片峰均来自麦氏重排和异构化后的α_裂解,由其裂解产生的m/z120和m/z163离子是该类化合物共同的特征离子 ;吡嗪酮苯甲酰基衍生物基峰为M -82 ,苯乙酰基类衍生物基峰为m/z245。     

电喷雾离子源正离子模式下环烯醚萜苷的质谱裂解行为

利用高分辨率四极杆-飞行时间串联质谱(Q-TOF MS/MS)对环烯醚萜苷同系组分7,8-环戊烯型和环戊烷型环烯醚萜苷在电喷雾正离子(ESI⁺)模式下的质谱裂解行为进行了研究. 在ESI⁺模式下, 环烯醚萜苷主要的质谱裂解途径是脱去母环上的功能基团, 如丢失H₂O, CO₂, CH₃OH, CH₃COOH和糖单元部分等, 由于它们均为葡萄糖苷, 所以共有碎片离子[Glc+Na]⁺(m/z 185.0). 环烯醚萜苷母核环上半缩醛结构的异构化造成二氢吡喃环的断裂, 但未发现与苷元部分在负离子(ESI^-)模式下相同的其它断裂. 环烯醚萜苷在ESI⁺模式下的断裂途径特征性不如其在ESI^-模式下的明显, 且灵敏度比后者低.     

Fragmentation study of simvastatin and lovastatin using electrospray ionization tandem mass spectrometry

The fragmentation mechanism of simvastatin and lovastatin was investigated using both triple quadrupole and ion trap mass spectrometers. The elimination of the ester side-chain followed by dehydration and dissociation of the lactone moiety were observed as the main fragmentation pathways for both compounds. Another major fragmentation process was a C==C double-bond facilitated rearrangement. Our tandem mass spectrometric (MS/MS) data suggested that the beta-hydroxy group was involved in the fragmentation by interacting with the carboxyl group generated from the ring opening of the lactone. As a result, a facile neutral loss of 60 Da (CH(3)COOH or a combination of CH(2)==C==O and H(2)O) was detected. MS/MS studies of the structural analogs also provided evidence that the dehydration of the beta-hydroxy lactone generated preferentially the beta,gamma-unsaturated lactones.     

Nitramine anion fragmentation: A mass spectrometric and Ab initio study

The fragment ion formation characteristics of the radical anions generated from hexahydro-1,3,5-trinitrotriazine (RDX) and its three nitroso metabolites were studied using GC/MS with negative chemical ionization (NCI) to understand the fragmentation mechanisms responsible for the formation of the most abundant ions observed in their NCI mass spectra. Ab initio and density functional theory calculations were used to calculate relative free energies for different fragment ion structures suggested by the m/z values of the most abundant ions observed in the NCI mass spectra. The NCI mass spectra of the four nitramines are dominated by ions formed by the cleavage of nitrogen-nitrogen and carbon-nitrogen bonds in the atrazine ring. The most abundant anions in the NCI mass spectra of these nitramines have the general formulas C(2)H(4)N(3)O (m/z 86) and C(2)H(4)N(3)O(2) (m/z 102). The analyses of isotope-labeled standards indicate that these two ions are formed by neutral losses that include two exocylic nitrogens and one atrazine ring nitrogen. Our calculations and observations of the nitramine mass spectra suggest that the m/z 86 and m/z 102 ions are formed from either the (M--NO)(-) or (M--NO(2))(-) fragment anions by a single fragmentation reaction producing neutral losses of CH(2)N(2)O or CH(2)N(2)O(2) rather than a set of sequential reactions involving neutral losses of HNO(2) or HNO and HCN.     

甾族化合物不对称合成的研究XV: 光学活性3-氧杂-A-失碳甾族化合物的合成

我们在寻找新的甾体口服避孕药的研究中,设计了A-失碳-3,9(10)-二烯-18-甲基甾体(1)作为全合成研究的目的物.前文已报道从5’-甲基呋喃二噻烷阴离子2b与消旋甾体CD环合成原3b的共轭加成,合成了两个新的消旋3-氧杂-A-失碳甾体4b和5b.本文报道     

The behavior of oxygen as a collision-induced dissociation target gas

The unusual and unique ability of O2 as target gas in kV collision-induced dissociations, to enhance a specific fragmentation of a mass selected ion, has been examined in detail. The affected dissociations studied were the loss of CH3* from CH3CH+X (X = OH, CH3, NH2, SH); CH3* and C1* loss from CH3C+(C1)CH3; C2H5* loss from CH3CH2CH+X (X = OH and NH2); H* loss from +CH2OH and +CH2NH2; O loss from 1,2-, 1,3-, and 1,4-C6H4(NO2)2+*; CH3NO+*; C6HsNO2+*; C5H5NO+* (pyridine N-oxide); 3- and 4-CH3C5H4NO+*. A general explanation of the phenomena, which was semiquantitatively tested in the present work, can be summarized as follows: the ion - O2 encounter excites the target molecules to their 3sigma(g)- state which resonantly return this energy to electronic state(s) in the ion. The excited ion now contains a sharp excess of a narrow range of internal energies, thus significantly and only enhancing fragmentations whose activation energies lie within this small energy manifold.     

(+)-Silybin, a pharmacologically active constituent of Silybum marianum: fragmentation studies by atmospheric pressure chemical ionization quadrupole time-of-flight tandem mass spectrometry

The fragmentation behavior of (+)-silybin (1) and (+)-deuterosilybin (2), as well as of their flavanone-3-ol-type building blocks, such as 3,5,7-trihydroxy-2-phenyl-4-chromanone (3) and 2-(1,4-benzodioxolanyl)-3,5,7-trihydroxy-4-chromanone (4), were investigated by atmospheric pressure chemical ionization quadropole time-of-flight tandem mass spectrometry in the positive ion mode (APCI(+)-QqTOF MS/MS). The product ion spectra of the protonated molecules of 1 revealed a rather complicated fragmentation pattern with product ions originating from consecutive and competitive loss of small molecules such as H2O, CO, CH2O, CH3OH and 2-methoxyphenol, along with the A+- and B+-type ions arising from the cleavage of the C-ring of the flavanone-3-ol moiety. The elucidation of the fragmentation behavior of 1 was facilitated by acquiring information on the fragmentation characteristics of the flavanone-3-ol moieties and 2. The capability of the accurate mass measurement on the quadrupole time-of-flight mass spectrometer allowed us to determine the elemental composition of each major product ion. Second-generation product ion spectra obtained by combination of in-source collision induced dissociation (CID) with selective CID (pseudo-MS(3)) was also helpful in elaborating the fragmentation pathways and mechanism. Based on the experimental results, a fragmentation mechanism as well as fragmentation pathways for 1 and its flavanone-3-ol building blocks (3, 4) are proposed and discussed.     

Unimolecular reactions of \documentclass{article}\pagestyle{empty}\begin{document}$ ^ \cdot {\rm CH}_2 {\rm CH}_2 \mathop {\rm O}\limits^ + {\rm HCH}_2 {\rm CH}_2 {\rm CH}_3 $\end{document} β?distonic ion

The β-distonic ion $ ^ \cdot {\rm CH}_2 {\rm CH}_2 \mathop {\rm O}\limits^ + {\rm HCH}_2 {\rm CH}_2 {\rm CH}_3 $ has been shown previously to be an intermediate in the fragmentation of ionized ethyl propyl ether. The reactions of this ion (generated by fragmentation in the ion source of alkyl propyl ethers of glycol) were studied in this work. Labelling showed that this ion undergoes competing hydrogen transfers leading to a series of isomeric distonic ions. Each of them was submitted to an isotope effect.     

Endgroup-assisted siloxane bond cleavage in the gas phase

Unimolecular dissociation of H(2)N(CH(2))(3)SiOSi(CH(2))(3)NH(3)(+) generates SiC(5)H(16)NO(+) and SiC(5)H(14)N(+). The formation of SiC(5)H(16)NO(+) involves dissociation of a Si[bond]O bond and formation of an O[bond]H bond through rearrangement. The fragmentation mechanism was investigated utilizing ab initio calculations and Fourier transform ion cyclotron resonance (FTICR) mass spectrometry in combination with hydrogen/deuterium (H/D) exchange reactions. Sustained off-resonance irradiation collision-induced dissociation (SORI-CID) studies of the fully deuterated ion D(2)N(CH(2))(3)SiOSi(CH(2))(3)ND(3)(+) provided convincing evidence for a backbiting mechanism which involves hydrogen transfer from the terminal amine group to the oxygen to form a silanol-containing species. Theoretical calculations indicated decomposition of H(2)N(CH(2))(3)SiOSi(CH(2))(3)NH(3)(+) through a backbiting mechanism is the lowest energy decomposition channel, compared with other alternative routes. Two mechanisms were proposed for the fragmentation process which leads to the siloxane bond cleavage and the SORI-CID results of partially deuterated precursor ions suggest both mechanisms should be operative. Rearrangement to yield a silanol-containing product ion requires end groups possessing a labile hydrogen atom. Decomposition of disiloxane ions with end groups lacking labile hydrogen atoms yielded product ions from direct bond cleavages.     

Sites of reaction of pilocarpine

Analysis of the sites of reaction of a biologically important compound, pilocarpine, a molecule with imidazole and butyrolactone rings connected by a methylene bridge, has been accomplished in a quadrupole ion trap with the aim of characterizing its structure/reactivity relationships. Ion-molecule reactions of pilocarpine with chemical ionizing agents, dimethyl ether (DME), 2-methoxyethanol, and trimethyl borate (TMB), along with collision-activated dissociation elucidated the reaction sites of pilocarpine and made possible the comparison of structural features that affect sites of reaction. Based on MS/MS experiments, methylation occurs on the imidazole ring upon reactions with CH3OCH2+ or (CH3OCH2CH2OH)H+ ions but methylation occurs on the lactone ring for reactions with (CH3O)2B+ ions. Bracketing experiments with two model compounds, alpha-methyl-gamma-butyrolactone and N-methyl imidazole, show the imidazole ring to have a greater gas-phase basicity and methyl cation affinity than the lactone ring. The contrast of methylation by TMB ions on the lactone ring is explained by initial addition of the dimethoxyborinium ion, (CH3O)2B+, on the imidazole ring with subsequent collisional activation promoting an intramolecular transfer of a methyl group to the lactone ring with concurrent loss of CH3OBO. Semiempirical molecular orbital calculations are undertaken to further address the favored reaction sites.     

Electron ionization mass spectra of phosphorus-containing heterocycles. I. 1,4,4a,5,6,7,8,8a-octahydro-2H-3,1,2-benzoxazaphosphinine 2-oxides

The electron ionization mass spectra of 27 cis- and trans-annelated 1,4,4a,5,6,7,8,8a-octahydro-2H-3,1,2-benzoxazaphosphinine 2-oxides were recorded to clarify the effects of the ring heteroatom (O or N), ring annelation, the P configuration and the substituents attached to the ring or to the N and P atoms. For compounds 1-12 different alkyl radical and alkene losses and the cleavage of the P-heteroatom bonds, instead of the P-C bonds, were representative and dependent mainly on the substitution on the N and P atoms. The replacement of Ph and OPh by N(CH2CH2Cl)2 on the P atom had a dramatic influence on the fragmentation process: new fragment ions were obtained and very little M+ (1-3%) was formed. Only slight differences were found between some of the corresponding isomers, but interestingly the compounds formed clear groups on the basis of the differences in their fragmentation, depending on the ring-N and ring-P substituents.