Mass spectrometric investigation of the catalysis of secondary processes of decomposition of ammonium perchlorate

Russian Chemical Bulletin -     

Mass spectrometric decomposition of Β-phenyloxiranecarboxylic esters

The electron-impact mass spectra of the E- and Z-isomers of the ,-methyl substituted esters of -phenyloxiranecarboxylic acids have been studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1310–1314, October, 1986.     

Mass spectrometric fragmentation patterns of isomeric 5-methyl-3-alkyl-2-alkenylpyrazines

The detailed mass spectral fragmentation pathways of a series of both naturally occurring and synthetic 5-methyl-3-alkyl-2-aIkenylpyrazines have been elucidated with the aid of deuterium labels placed specifically in the alkenyl side-chain. The influence on the fragmentation pattern of the stereochemistry of the alkenyl group as well as the relative placement of the groups on the pyrazine nucleus have also been evaluated. This provides information of some diagnostic value in the assignment of structures by mass spectrometry to new compounds within this class.     

Mass spectrometric decomposition of 2-dimethylamino-4-methoxy-6-polynitromethyl-1,3,5-triazines

Fragmentation of 6-fluoro(chloro, bromo)dinitromethyl-, 6-trinitromethyl-, 6-(1,1-dinitroethyl)-, and 6-(2-hydroxy-1,1-dinitroethyl)-2-dimethylamino-4-methoxy-1,3,5-triazines under electron impact was studied. The stability of the molecular ions and main fragmentation pathways are discussed.     

Mass spectrometric studies of some 4-acyl substituted 1-phenyl-3-methyl-5-pyrazolones

The electron-impact-induced fragmentation of 1-phenyl-3-methyl-5-pyrazolone and six 4-acyl substituted derivatives, have been studied with the aid of deuterium labelling, high resolution mass measurements and the metastable defocusing technique. The mass spectra of the pure keto and the pure enol forms do not show any significant differences. The predominant decomposition of the 4-acyl substituted pyrazolones is the α-cleavage with respect to the carbonyl group leading to intense peaks at m/e 201 by loss of the alkyl group. In the case of benzoyl and ethoxycarbonyl derivatives the α-cleavage is associated with a specific hydrogen rearrangement causing the loss of a benzene and an ethyl alcohol molecule, respectively.     

Mass spectrometric analysis of ceramics after decomposition with elemental fluorine

The features of a combustion with elementary fluorine for the case of compact SiC ceramics and model substances for boron containing ceramics (H₃BO₃ and Na₂B₄O₇) were investigated with the aim of their decomposition and analysis. On-line detection of the gaseous decomposition products by quadrupole mass spectrometry using electron impact ionisation was studied. Limitations by blanks and transport interferences were investigated. Standard addition as well as the isotope dilution technique were used for calibration in the case of B, C and W at the trace and major component level.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthdayDeceased May 1995.     

Mass spectrometric studies of 2-nitrosophenols

The mass spectra of 2-nitrosophenols are independent of the insertion temperature, suggesting that the compounds either do not exhibit tautomerism in the vapour phase or that the enthalpy of isomerization is low. However, their fragmentation patterns suggest tautomerism in the molecular ion.     

Mass spectrometric study of 2-azafluorenes

The fragmentation of 2-azafluorene and its methyl and phenyl-substituted derivatives was studied. It is shown that ejection of an RCN fragment (R=CH₃, C₆H₅) by the molecular ions leads to a more intense peak if R is in the 3 position of the azafluorene ring. It was established that, in contrast to the dissociative ionization of fluorene, all of the ions of which are formed from the (M-H)⁺ fragment, the fragmentation of 2-azafluorene and its derivative also takes place from the molecular ion. Randomization of the deuterium atoms attached to C₉ with the remaining hydrogen atoms was observed.Translated from Khimiya Geterotisiklicheskikh Soedinenii, No. 1, pp. 101–105, January, 1977.     

Mass spectrometric studies on the decomposition of trialkylgallium on gaas surfaces

The thermal decomposition of trimethylgallium [(CH₃)₃Ga] and triethylgallium [(C₂H₅)₃Ga] on gallium arsenide (GaAs) surfaces was studied under an ultra-high vacuum using mass spectrometry. It was observed that the decomposition process of (CH₃)₃Ga and (C₂H₅)₃Ga depends on the arsenic coverage of the substrate surface. On a (100)-oriented surface, increasing the arsenic coverage basically enhances the decomposition of (CH₃)₃Ga and (C₂H₅)₃Ga to gallium atoms above 350 and 300°C, respectively. The decomposition of (CH₃)₃Ga proceeds by emitting CH₃ radicals. On a surface with low arsenic coverage, the decomposition of (CH₃)₃Ga is imperfect and fewer than three methyl groups of alkylgallium are desorbed. On a (111)B-oriented surface, however, an increase in the surface arsenic coverage suppresses the decomposition of alkylgallium, which is different from the case for a (100) surface.     

Competitive hydrogenation of 2-methyl-3-butene-2-ol and 1-hexene on a platinum catalyst modified by amines

The effect of the amount of diethylamine and triethylamine on the degree of poisoning of a hydrogenation catalyst 10% Pt on silica gel was examined. The dependence of the selectivity of competitive catalytic hydrogenation of 2-methyl-3-butene-2-ol and 1-hexene in methanol and cyclohexane on the degree of poisoning was investigated.

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(10% Pt ), 2--3--2- 1- .

     

Mass spectrometric kinetic analysis of human tyrosylprotein sulfotransferase-1 and -2

Protein tyrosine O-sulfation, a widespread post-translational modification, is mediated by two Golgi enzymes, tyrosylprotein sulfotransferase-1 and-2. These enzymes catalyze the transfer of sulfate from the universal sulfate donor 3′-phosphoadenosine-5′-phosphosulfate (PAPS) to the hydroxyl group of tyrosine residues to form tyrosine O-sulfate ester and PAP. More than 60 proteins have been identified to be tyrosine sulfated including several G protein-coupled receptors, such as CC-chemokine receptor 8 (CCR8) that is implicated in allergic inflammation, asthma, and atherogenesis. However, the kinetic properties of purified tyrosylprotein sulfotransferase (TPST)-1 and −2 have not been previously reported. Moreover, currently there is no available quantitative TPST assay that can directly monitor individual sulfation of a series of tyrosine residues, which is present in most known substrates. We chose an MS-approach to address this limitation. In this study, a liquid chromatography electrospray ionisation mass spectrometry (LC/ESI-MS)-based TPST assay was developed to determine the kinetic parameters of individual TPSTs and a mixture of both isozymes using CCR8 peptides as substrates that have three tyrosine residues in series. Our method can differentiate between mono-and disulfated products, and our results show that the K_m,app for the monosulfated substrate was 5-fold less than the nonsulfated substrate. The development of this method is the initial step in the investigation of kinetic parameters of the sequential tyrosine sulfation of chemokine receptors by TPSTs and in determining its catalytic mechanism.     

Effect of composition of the solvent on the selectivity of competitive hydrogenation of 2-methyl-3-butene-2-ol and 1-hexene

The selectivity of competitive hydrogenation of 2-methyl-3-butene-2-ol and 1-hexene on 5% Pt on silica gel catalyst at 20°C and atmospheric pressure was investigated, and the effect of changes in the composition of the solvent on the selectivity of hydrogenation was examined. Three solvent systems have been used: methanol-water, 1-heptanol-cyclohexane and ethanol-cyclohexane mixtures. The causes underlying changes in the selectivity of hydrogenation with changing composition of the solvent are discussed.

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2--3--2- 1- 5% Pt 20°C . . 1- . .

     

Mass spectrometric study of 1-chloro-2-nitrosocycloalkanes,dimers in gaseous phase

The electron-impact mass spectra and the field ionization mass spectra of 1-chloro-2-nitrosocyclohexane and 1-chloro-2-nitrosocyclopetane are presented and discussed. The two compounds investigated exist in dimeric form in the gaseous phase.