The mass spectra of 2,4,7-trihydroxypteridines and their trimethylsilyl derivatives

The mass spectra of a series of 2,4,7-trihydroxypteridines and their trimethylsilyl derivatives have been determined. Fragmentation mechanisms are supported by high resolution, deuterium labeling and metastables.     

Identification of phosphorylcholine substituted peptides by their characteristic mass spectrometric fragmentation

Phosphorylcholine (PC) substituted biomolecules are wide-spread, highly relevant antigens of parasites, since this small hapten has been found to be a potent immunomodulatory component which allows the establishment of long lasting infections of the host. Structural data, especially of protein bound PC-substituents, are still rare due to the observation that mass spectrometric analyses are mostly hampered by this zwitterionic substituent resulting in low sensitivities and unusual but characteristic fragmentation patterns. Here we investigated the fragmentation behaviour of synthetic PC-substituted peptides by matrix-assisted laser desorption/ionization mass spectrometry and electrospray ionization ion trap mass spectrometry. We could show that the predominant neutral loss of a trimethylamine unit (Hoffmann elimination) leads to cyclic phosphate derivatives which prevent further fragmentation of the peptide backbone by stabilizing the positive charge at this particular side chain. Knowledge of this PC-specific fragmentation might help to identify PC-substituted biomolecules and facilitate their structural analysis.     

Cyclic ions in the mass spectra of trimethylsilyl derivatives of substituted o-dihydroxybenzenes

The mass spectra of trimethylsilyl (TMS) ethers/methyl esters of phenolic acids containing o-dihydroxybenzene groups have base peaks at [M?119]⁺ instead of the usual [M?15]⁺ and [M?31]⁺ that are characteristic of TMS/methyl esters of monohydroxyphenolic acids. These ions, formed by the loss of 31+88 u from the parent ion, possess a cyclic moiety as proven by substitution of deuterium atoms for hydrogen atoms in the TMS groups of the methyl esters of 3,4,5-trihydroxybenzoic (gallic), 3,4-dihydroxybenzoic (protocatechuic) and β-(3,4-dihydroxyphenyl)propenoic (caffeic) acids. Although these cyclic ions are the base peaks in TMS-derivatized o-dihydroxyphenolic acid esters, similar ions represent intense peaks but not necessarily the base peak in other derivatized compounds such as 1,2-dihydroxybenzene, 1,2-dihydroxy-3-methyl- and 1,2-dihydroxy-4-methyl-benzenes and flavan-3-ols that possess o-dihydroxybenzene groups. Compounds possession m- or p-dihydroxybenzene groups do not form these cyclic ions; therefore, this procedure for derivatization and interpretation of mass spectra is valuable for the identification of compounds containing o-dihydroxybenzene groups in complex mixtures of isomeric compounds.     

The mass spectra of some N-substituted barbitals and their trimethylsilyl derivatives

The mass spectra of N-propyl and N-butyl barbitals show the loss of olefin radical (C_nH_2n-1) in analogy to structurally similar molecules such as N-alkyl succinimides and 3-alkyl uracils. Trimethylsilylation of the N-substituted barbitals suppresses this fragmentation and loss of olefin via apparent McLafferty rearrangement from the even-electron ion, [M – 15]⁺, becomes significant. The trimethylsilyl derivatives of N-allyl barbital and N-phenyl barbital show an unusually facile elimination of the appropriate isocyanate from the molecular ion.     

土槿皮酸类化合物的质谱研究

本文系统地研究了土槿皮甲酸、乙酸和丙酸及其衍生物的质谱.通过质谱-结构关系的分析、高分辨质谱及亚稳数据的测定,阐明了它们在电子轰击下的裂解反应机制.     

Cluster ions of diquat and paraquat in electrospray ionization mass spectra and their collision-induced dissociation spectra

Cluster ions such as [Cat+X+nM](+) (n = 0-4); [Cat-H+nM](+) (n = 1-3); and [2(Cat-H)+X+nM](+) (n = 0-2), where Cat, X, and M are the dication, anion, and neutral salt (CatX(2)), respectively, are observed in electrospray ionization (ESI) mass spectrometry of relatively concentrated solutions of diquat and paraquat. Collision-induced dissociation (CID) reactions of the clusters were observed by tandem mass spectrometry (MS/MS), including deprotonation to form [Cat-H](+), one-electron reduction of the dication to form Cat(+.), demethylation of the paraquat cation to form [Cat-CH(3)](+), and loss of neutral salt to produce smaller clusters. The difference in acidity and reduction power between diquat and paraquat, evaluated by thermodynamical estimates, can rationalize the different fractional yields of even-electron ([Cat-H](+) and its clusters) and odd-electron (mostly Cat(+)) ions in ESI mass spectra of these pesticides. The [Cat+n. Solv](2+) doubly charged cluster ions, where n 相似文献   

Multiply charged ions in field desorption mass spectra of peptides containing basic amino acids

Multiply charged ions up to [M+4]⁴⁺ were observed in the field desorption mass spectra of five different peptides. The relationship between the charge-multiplicity and the number of basic sidechains is discussed.     

Rearrangement ions in the mass spectra of bis- trimethylsilyl derivatives of simple boronic acids

The mass spectra of bis-trimethylsilyl derivatives of simple boronic acids have been determined and found to contain two rearrangement ions involving loss of MeBO. Mechanisms based largely on 1, 3 shifts to electron deficient silicon and boron are presented to explain the formation of these ions. The mechanisms are supported by deuterium labelling experiments and metastable transtions.     

The mass spectra of phenothiaphosphine derivatives

The molecular ion of the phenothiaphosphine derivatives is fairly stable. Under electronimpact, the phenothiaphosphines (I) and phenothiaphosphinic acids (IV, R = H) undergo a one-step elimination of the phosphorus atom together with the groups attached to it. Substitutents in the aromatic rings, as well as on the phosphorus, influence the fragmentation pattern; ring methyl, e.g. leads to tropylium structures. Phosphine oxides of type V lose RO˙, probably after a rearrangement, when R = aryl, but R˙ if it is methyl.     

Photoionization mass spectra of alicyclic compounds with various substituents,and their ionization energies and appearance energies

Conclusions We measured the ionization energies, the appearance energies, and the photoionization mass spectra of the oximes of cyclopentanone, cyclohexanone, cycloheptanone, cyclooctanone, and cyclododecanone and of some other compounds of the cyclooctane and cyclododecane series.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2602–2605, November, 1979.     

PMR spectra of catechins and their derivatives

Summary The PMR spectra of catechins, gallocatechins, epigallocatechin gallate, and their acetyl derivatives have been analyzed and the structures of the compounds investigated have been confirmed.The parameters of the signals of the H-2 and H-3 protons that have been found and also the nature of their change on acetylation enable a compound investigated to be assigned unambiguously to the normal or to the epi series.Division of Bioorganic Chemistry, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 46–50, January–February, 1976.     

Ge-substituted germatranes and their mass spectra

Conclusions The previously unknown Ge-substituted germatranes have been synthesized. The mass spectra of these compounds have been studied, and paths for their dissociative ionization are proposed.Translated fron Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1846–1849, August, 1979.     

Factors influencing the formation of some characteristic fragment ions in the mass spectra of 16-trimethylsilyloxy androstanes

The mass spectra of the trimethylsilyl derivatives of several steroids containing a 16-hydroxy function are presented. The mechanisms giving rise to various characteristic fragment ions were investigated with the aid of deuterium and ¹⁸O-labeling.     

The mass spectra of some pentafluorophenylthio derivatives

Ionic fragmentations induced by electron-impact on compounds of the type C₆F₅SX (X ? H, CH₃, COCH₃, Cl, C₆F₅) and (C₆F₅S)₂, (C₆F₅S)₂Hg, (C₆F₅S)₃As and (C₆F₅SCH₂)₂ have been studied. Principal features of the mass spectra are reported. The [C₆F₅S]⁺ ion (m/e 199) is predominant and its mode of fragmentation has been deduced. The precursor ions for m/e 199 have been examined in (C₆F₅)₂S, (C₆F₅S)₂, (C₆F₅S)₂Hg, (C₆F₅S)₃As and C₆F₅SCl. Ion kinetic energy spectra of (C₆F₅)₂S, (C₆F₅S)₂, (C₆F₅S)₂Hg and C₆F₅SCl have been recorded, and all contain peaks corresponding to the fragmentation of the [C₆F₅S]⁺ ion.     

Pyrolysis and mass spectra of trimethylsilyl derivatives of monosaccharides

The pyrolysis of trimethylsilyl derivatives of saccharides (1) was investigated by DTA-TG, MS, GC/MS and TG-GC/MS. The DTA-TG/DTG curves showed that the pyrolysis of 1 occurred in one stage. The exothermic peaks were due to sublimation or thermal decomposition by vaporization. The cleavage mechanism by electron impact of 1 was classified into four categories: 1) stepwise elimination of the side-chain, 2) cleavage of the side-chain, 3) cleavage of the pyranose ring, and 4) cleavage of the pyranose ring and side-chain at the same time. The mass-spectrum for 1 revealed the main common four fragment ions, such asm/z 73, 191, 204 and 217, with cleavage of the pyranose ring. These fragment ions were detected with a similar retention time in the gas cromatogram by GC/MS or TG-GC/MS. The retention time for 1 increased in the sequence aldopentose相似文献   

The mass spectra of halogeno derivatives of quinoxaline

The mass spectra of seventeen different quinoxaline halogeno derivatives are reported. The fragmentation mechanism is discussed.     

Infrared spectra of cyclic ethers and their derivatives

Data for the characteristic bands of cyclic ethers are reviewed. The infrared spectra of a number of 2-mono- and 2, 5-di-substituted derivatives of tetrahydrofuran are investigated. Absorption bands at about 900 cm⁻¹ are related to pulsation vibrations, and those at about 1200 cm⁻¹ to antisymmetric skeletal vibrations, of the tetrahydrofuran ring. It is shown that to confirm the presence of a tetrahydrofuran ring in a molecule, it is necessary to take into account not only the band of valence antisymmetric vibrations of the group C-O-C (ν _C-O-C ^as 1075 cm⁻¹), but also bands due to ring pulsation vibrations (ring symmetric valence vibrations ν _sk ^s ∼ 900 cm¹).