氮杂硅三环类化合物的质谱研究

本文对二十四个氮杂硅三环类化合物进行了质谱研究.测定了它们的低分辨质谱,收集了大部分化合物的高分辨质谱数据并进行了亚稳跃迁测定。结果表明,分子离子的稳定性、基峰的生成方式以及碎片离子的多少主要取决于取代基R的性质.分子的电子轰击质谱裂解存在三种基本方式:(1)断裂Si～R键,生成高度稳定的(M-R)~ 离子,碎片离子较少;(2)开环,失去碎片C_2H_3O;(3)开环,失去碎片CH_2O或CH_3O.用电荷自由基定域理论解释这类化合物的质谱裂解机理,并对影响分子离子稳定性的有关因素及影响基峰形成的原因进行了讨论.     

Electron impact fragmentation of some cyclohexyl thiophosphororganic amides

This paper presents the mass spectra, fragmentation pathways and structures of ions obtained by electron impact from methyl cyclohexyl phosphinomorpholinylamidothioate (1), cyclohexyl phosphonomorpholinylamidochloridothioate (2), cyclohexyl morpholinylamidophosphonothioic acid (3) and O-methyl cyclohexyl phosphonomorpholinylamidothioate (4). The fragmentation pathways and ion structures were established by exact mass determinations on compound 1 and by metastable transitions of all the compounds.     

Mass spectral study on O,O-dialkyl N,N-dialkyl phosphoramidates under electron impact conditions

A series of O,O-dialkyl N,N-dialkyl phosphoramidates (1-25) were analyzed under GC-EIMS conditions. Clear-cut differences are found in the fragmentation of O,O-dialkyl N,N-dimethyl phosphoramidates (Series 1) and O,O-dimethyl N,N-dialkyl phosphoramidates (Series 2). The phosphoramidates comprising of mixed/crossed alkyl groups on nitrogen and oxygen (Series 3) showed mixed fragmentation pattern corresponding to both Series 1 and 2 depending on the nature of alkyl groups. All the possible isomers among the studied compounds showed distinguishable EI mass spectra. Although the major ions in the EI mass spectra for the isomers containing O-n-propyl or O-isopropyl and N,N-diethyl or N-isopropyl N-methyl are similar, the isomers could be distinguished by characteristic ions of low abundance at low mass region. The differences are prominent in the metastable ion spectra of characteristic ions.     

Mass spectra of organolanthanide complexes

The EI mass spectra of seven 1,1′-(3-oxa-pentamethylene)-dicyclopentadienyl lanthanide and yttrium chlorides ( 1–7 ), and eleven dicyclopentadienyl lanthanide and yttrium chlorides ( 8–18 ) were investigated. Fragmentation patterns of these complexes were studied by using metastable ion measurements. The EI spectra of complexes 1–7 exhibited strong molecular ion peaks, the fragmentation of molecular ions were more complicated. The EI mass spectra of complexes 8–18 supported the dimeric structure under gaseous state. In the spectra of dimers (C₅H₅)₃LN⁺ observed were resulted from the skeletal rearrangement involving the migration of cyclopentadienyl moiety.     

Loss of isocyanic acid from the internal oxadiazole ring of protonated molecules of some 2,5-diaryl-1,3,4-oxadiazoles

The fragmentation pattern of some protonated 2,5-diaryl-1,3,4-oxadiazoles is discussed. An unusual decomposition consisting of elimination of the isocyanic acid molecule from the internal oxadiazole ring was found. This fragmentation pathway was deduced on the basis of B/E linked scan mass spectra of metastable ions with liquid secondary ion mass spectrometry as the ionization method and also of low-energy CID mass spectra where electrospray was used as the ionization technique. High resolution measurements were also performed.     

Mass spectra of 1-(2′-hydroxy-5′-alkylphenyl)-1-alkanone (E)-oximes

The mass spectra of 1-(2′-hydroxy-5′-alkylphenyl)-1-ethanone (E)-oximes 1–6 and 1-(2′-hydroxy-5′-methylphenyl)-1-alkanone (E)-oximes 7–12 are given and the major fragmentation pathways discussed. The simultaneous loss of water and alkyl moieties from the molecular ion indicates that a skeletal rearrangement take place and a cycloheptatrienyloheterocyclic system is formed. The McLafferty rearrangement, γ-fission in the side aliphatic chain and oxygen expulsion are discussed with evidence being drawn from accurate mass measurements, metastable ions and comparison with mass spectral data of related compounds.     

Differences in the mass spectra of isomeric benzolactams

It is shown that 3- and 4-substituted dihydro-2-quinolones can be distinguished from the isomeric dihydro-1-isoquinolones by mass spectrometry. The [M - CO]⁺ ion is characteristic for the mass spectra of dihydroquinolone derivatives, whereas retrodiene fragmentation of the molecular ion is characteristic for dihydroisoquinolone derivatives. The intense [M - R]⁺ and [M - R, - H₂O]⁺ ion constitute evidence that the substituent is located in the 3 (for dihydroisoquinolones) or 4 (for dihydroquinolones) position. The processes that occur in the fragmentation were confirmed by data from the high-resolution mass spectra, an analysis of the observed metastable ions, and an analysis of the mass spectra of 3-methyl-3,4-dihydro-1-isoquinolone and 4-methyl-3,4-dihydro-2-quinolone containing deuterium attached to the nitrogen atoms.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 246–249, February, 1979.     

High pressure matrix-assisted laser desorption/ionization Fourier transform mass spectrometry for minimization of ganglioside fragmentation

Transiently elevating pressure in a matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS) source into the 1-10 mbar range during ionization decreases the metastable fragmentation of gangliosides. This allows detection of the molecular ion species without loss of the highly labile sialic acid residues. In these experiments, gangliosides with up to five sialic acids were ionized by MALDI and detected with the FTMS. In each case, when the high pressure collisional cooling was used, the singly charged molecular ion was the base peak in the spectra, both in the positive and negative ion modes, and minimal metastable fragmentation was observed. This result is promising, as the previously developed TLC separation methods can be coupled to MALDI-FTMS.     

芳香族羟肟及其过渡金属配合物的质谱研究

本文报道某些芳香族羟肟及其过渡金属铜、镍、钴和铁配合物的EI质谱,借助亚稳跃迁、高分辨质谱和稳定同位素^1^5N、^6^3Cu、和^6^5Cu标记物,讨论其断裂途径,总结断裂规律.     

Sequence analysis for an unknown peptide by molecular secondary ion mass spectrometry

Positive and negative molecular secondary ion as well as metastable ion mass spectra for various peptides are investigated to clarify their fragmentation regularity. The fragmentation regularity is derived by considering all the possible bond cleavages at the peptide bond or at the adjacent bonds. It is demonstrated that the amino acid sequence for an unknown peptide can be determined by interpreting the positive and negative secondary ion and metastable ion mass spectra using this fragmentation regularity.     

A study of b<Subscript>1</Subscript>+H<Subscript>2</Subscript>O and b<Subscript>1</Subscript>-ions in the product ion spectra of dipeptides containing N-terminal basic amino acid residues

The product ion spectra of approximately 200 dipeptides were acquired under low-energy conditions using a triple quadrupole mass spectrometer. The spectra of dipeptides containing an N-terminal arginine (R), histidine (H), or lysine (K) were observed to yield a b(1) + H(2)O ion corresponding to the protonated basic amino acid. This was equivalent to the y(1)-ion in the corresponding C-terminal isomer. The formation of a b(1) + H(2)O ion was not a significant fragmentation channel in any dipeptides analyzed including those containing a C-terminal basic amino acid unless they also contained an N-terminal basic amino acid. Occurring simultaneously and under equal energy conditions an apparent b(1)-ion was formed, which has its corresponding C-terminal equivalent in the y(1)-H(2)O ion. Energy resolved mass spectrometry (ERMS), deuterium labeling, and accurate mass experiments as well as data reported were used to show the relationships between the b(1)+H(2)O and b(1)-ions in the dipeptides containing an N-terminal basic amino acid and the y(1) and y(1)-H(2)O ions in the corresponding C-terminal isomers.     

Electron ionisation mass spectral analysis and fragmentation pathways for some thiophosphorylic p-carboxybenzene sulfonamides

The work presents the 70 eV electron impact mass spectra of some thiophosphorylic p-carboxybenzene sulfonamides, and proposes rationalisation of their fragmentation pathways. Accurate mass measurements of the fragment ions, and metastable ion analyses performed in the MIKES mode, were used to elucidate the most abundant ion compositions and to elucidate the fragmentation patterns of these pharmacologically interesting compounds.     

Fragmentation and rearrangement reactions in certain 1,2,3-triaryl-2-propen-1-ones following electron impact and chemical ionization

The electron impact (EI) and chemical ionization (CI) mass spectra of certain 1,2,3-triaryl-2-propen-1-ones (TAPs) have been studied in detail with the help of exact mass measurements, deuterium labelling and metastable data. The E- and Z-isomeric pairs do not show any difference in their behaviour under EI or CH₄ CI conditions. EI-induced rearangement reactions in the TAPs include aryl migration to carbonium ion centres. A study of the metastable transitions reveals aryl group interchange in the molecular ions prior to fragmentation. Under EI conditions loss of arene involves either C(2) or C(3) aryl groups while under CI conditions the C(1) aryl is lost as a neutral arene molecule. Mechanisms for the different fragmentation modes are given.     

Evidence for an aryl migration during the electron impact induced fragmentation of substituted aryloxymethylquinoxalines.

The electron impact (EI) mass spectra of 34 differently substituted 2-phenoxymethyl-, 2-naphthyloxymethyl-, 2-pyridinyloxymethyl- and 2-chinolinyloxymethylquinoxalines were recorded. The fragmentation patterns were examined by metastable ion analysis and exact mass measurements, employing finally also selective deuterium labelling. The inclusion of the substituted aryl ring moiety appears to be important for the fragmentation of the aryloxymethylquinoxalines. A molecular ion rearrangement is proposed for the observed loss of OH* and CHO* radicals. The influence of the different substituents on the aryl ring moiety on the rearrangement in the gas phase and on the resulting fragmentation was investigated.     

Metastable ion and induced stable ion fragmentation of isomeric 5-methyl-3-tolyl-1,2,4-oxadiazoles

The electron ionization fragmentation patterns of 5-methyl-3-(o-, m- and p-tolyl)-1,2,4-oxadiazoles (1a—c) have been examined by metastable ion and high resolution mass spectrometry. The o-tolyl isomer loses CO and C₂H₂O from the metastable molecular ion whereas the m- and p-tolyl isomers lose only CH₃CN thus indicating a strong ortho effect in directing the fragmentation in 1a. Slight differences between o-, m- and p-tolyl isomers in the collisional activation fragmentation of stable [C₇H₆N]⁺ ions suggest that structural differences exist even after a series of extensive rearrangements of the molecular ions. Metastable ion kinetic energy (MIKE) and collisional activation (CA) spectra were very helpful in providing valuable information about many fragments.     

Electron-impact induced rearrangements in isomeric pyridine aldoximes

The mass spectra of α-, β- and γ-pyridine aldoximes and the respective O-methyl ethers were studied. The mass spectral behaviour of α-pyridine aldoxime is characterized by the elimination of NO, while the molecular ion of the γ-isomer expels H₂ CN. In the case of the β-isomer the formation of the m/e 67 ion (C₄H₅N) in a concerted process is the main feature. In the α-pyridine aldoxime methyl ether, in sharp contrast to the hydroxy analog, the M-30 peak was found to be due to the elimination of CH₂O, the expulsion of NO being absent. The mechanism of the fragmentation reactions is discussed, the conclusion drawn being based on the high resolution measurements as well as on the spectra of the respective deuterioanalogs and on the metastable transitions.     

Electron impact-induced fragmentation of 2,1-benzisothiazoline 2,2-dioxide

The electron impact-induced fragmentation patterns of 2,1-benzisothiazoline 2,2-dioxide nitro derivatives were studied. The rationalizations proposed for the fragmentations are supported by accurate mass measurements, daughter ion (mass analysed ion kinetic energy and B/E linked-scan), parent ion, and constant neutral loss spectra in metastable and collision-induced dissociation modes and deuterium labelling.     

(+)-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.     

Mass spectral studies of some 1,2,4-oxa-(thia)diazol-5(4H)-ones(thiones)

Electron ionization mass spectra of some 3,4-disubstituted 1,2,4-oxadiazole-5(4H)-thiones, thiadiazol-5(4H)-ones and thiadiazole-5(4H)-thiones are reported and fragmentation pathways of their molecular ions are studied in view of metastable ion experiments and accurate mass measurements. The main fragmentation route of the compounds under investigation is retro 1,3-dipolar cycloaddition.     

Differentiating alpha- and beta-aspartic acids by electrospray ionization and low-energy tandem mass spectrometry

Spectra obtained by low-energy electrospray ionization tandem mass spectrometry (ESI-MS/MS) of 34 peptides containing aspartic acids at position n were studied and unambiguously differentiated. beta-Aspartic acid yields an internal rearrangement similar to that of the C-terminal rearrangements of protonated and cationized peptides. As a result of this rearrangement, two different ions containing the N- and the C-terminal ends of the original peptide are formed, namely, the bn-1 + H2O and y"l - n + 1 - 46 ions, respectively, where e is the number of amino acid residues in the peptide. The structure suggested for the y"l - n + 1 - 46 ion is identical to that proposed for the vn ions observed upon high-energy collision-induced dissociation (CID) experiments. The intensity of these ions in the low-energy MS/MS spectra is greatly influenced by the presence and position of basic amino acids within the sequences. Peptides with a basic amino acid residue at position n - 1 with respect to the beta-aspartic acid yield very intense bn-1 + H2O ions, while the y"l - n + 1 - 46 ion was observed mostly in tryptic peptides. Comparison between the high- and low-energy MS/MS spectra of several isopeptides suggests that a metastable fragmentation process is the main contributor to this rearrangement, whereas for long peptides (40 AA) CID plays a more important role. We also found that alpha-aspartic acid containing peptides yield the normal immonium ion at 88 Da, while peptides containing beta-aspartic acid yield an ion at m/z 70, and a mechanism to explain this phenomenon is proposed. Derivatizing isopeptides to form quaternary amines, and performing MS/MS on the sodium adducts of isopeptides, both improve the relative intensity of the bn + 1 + H2O ions. Based on the above findings, it was possible to determine the isomerization sites of two aged recombinant growth proteins.