摘要:

AbstractFast‐atom bombardment (FAB) mass spectra have been measured for resolved 132‐hydroxychlorophyllaepimers. The fragmentation of each epimer was studied by tandem mass spectrometry using linked scans at constant B/E. The FAB spectra showed a very intense radical cation (M+·) and EI‐type fragmentations. The most abundant fragment ions were formed by the losses of the phytyl, the 132‐hydroxy, and the 132‐methoxycarbonyl groups in various combinations. The fragment ions [M  OH]+, [M  phytadiene]+·, and [M  phytadiene  OH]+were found to be characteristic of both 132‐hydroxychlorophyllaepimers. Nevertheless, it was shown that the loss of the 132‐hydroxy group occurs more easily from the 132(S)‐epimer than from the 132(R)‐epimer. This fragmentation difference offers a new possibility for the determination of the stereochemistry at the 132‐chiral centre of purified 132‐

ISSN:0951-4198    

DOI:10.1002/rcm.1290090702

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractPyrolysis/gas chromatography/mass spectrometry (PY/GC/MS) of As4S6(orpiment), As4S4(realgar), As4O6(arsenolite), NaH2AsO4(sodium di‐H‐orthoarsenate) was performed using a platinum‐filament pyrolyzer heated at 700°C for 10 s and coupled to a capillary gas chromatograph/ion trap mass spectrometer. As4was observed as a pyrolysis fragment in the pyrograms of all compounds. Pyrolysis of NaH2AsO4equivalent to 100 ng of As, produced a strong As4chromatographic peak. As4S3and As4S4were detected as pyrolysis products of As4S6(orpiment). As4S4(realgar) and As4O6(arsenolite) were detected as intact molecules after pyrolysis. By contrast, intact As4S6was not detected after pyrolyses in the range 400–700°C. As4was detected as an impurity in the painting layer of an Egyptian mummy. The mass spectra of such arsenic compounds, none of which is included in the NIST library of spectra, are reported. Advantages and limitations of PY/GC/MS as a technique for the qualitative detection of arsenic inorganic compounds are

ISSN:0951-4198    

DOI:10.1002/rcm.1290090703

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractHuman fibroblast collagenase belongs to a family of matrix metalloproteinases which have been implicated in a number of connective tissue disorders ranging from rheumatoid arthritis to tumor invasion. To examine the active site of this enzyme by biophysical studies, a 19 kDa recombinant truncated mature collagenase (mCL‐t) was prepared. Electrospray ionization (ESI) and matrix‐assisted laser desorption/ionization (MALDI) mass spectrometry have been utilized for the characterization of mCL‐t. The molecular weights measured by these techniques identified the presence of two closely related protein components separated by approximately 100 Da. Edman sequence analysis demonstrated that the two protein components differ from each other by an amino terminal valine, consistent with the mass spectrometric data. In addition, the molecular weight of mCL‐t determined by mass spectrometry did not agree with that calculated from the reported sequence. To identify the origin of this discrepancy, the DNA sequence of the mCL‐t clone was examined. Several differences were noted between the DNA sequence of mCL‐t and the published collagenase gene sequence. When these differences were taken into account, the measured molecular weights were found to be in good agreement with that calculated for the modified sequence. In separate experiments, both ESI and MALDI mass spectrometry have been used to determine molecular weights of mCL‐t samples enriched with stable isotopes15N and (15N+13C). The measured molecular weights demonstrated a 97% (15N) and 99% (15N+13C) incorporation of labeled isotopes in th

ISSN:0951-4198    

DOI:10.1002/rcm.1290090704

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractThe formation of singly charged oligomers and multiply charged monomers has been studied under different conditions with matrix‐assisted laser desorption/ionization and it has been found that the concentration of analyte in matrix solution, as well as the matrix and substrate used, are factors that influence this process. The concentration of analyte in the matrix solution has a strong influence on the formation of singly charged oligomers. When α‐cyano‐4‐hydroxycinnamic acid is used as matrix, more doubly charged monomeric molecular ions are observed than when sinapinic acid is used. By using a nitrocellulose membrane instead of a silver plate as substrate, we find more multiply charged monomers and dimers in the spectra, especially in the case of high mass proteins, such as albumin. It seems that the formation of multiply charged monomers and oligomers is influenced by the overall amount of charge that the sample

ISSN:0951-4198    

DOI:10.1002/rcm.1290090705

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractThe mass spectrometric behavior of some diene‐based sex pheromones of lepidopterous insects, under electron impact ionization conditions, was studied with the aid of mass‐analyzed ion kinetic energy spectroscopy and high‐resolution data. The similarity of the mass spectra of these dienes and their ability to distinguish double bond positional isomers and geometrical isomers was examined by a ‘minimum‐maximum’ similari

ISSN:0951-4198    

DOI:10.1002/rcm.1290090706

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractThe charge transfer reactions of H 2+, CH 4+, CH 2+and N+ions with CH4, CH3D, CH2D2and CD4were studied. The measurements were carried out using a tandem type mass spectrometer. The influence of the kinetic and internal energy of the incident ions was observed on the secondary mass spectra and also on the isotope effects expressed through πi(D/H), Ti(H) and Ti(D) factors. The dependence of the isotope effects on kinetic energy could indicate a conversion of kinetic energy into internal energy. Reactions in which momentum transfer resulted in charge transfer were also observed, probably indicating a ‘short‐range interaction’ reacti

ISSN:0951-4198    

DOI:10.1002/rcm.1290090707

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractThermal transformations of phosphorus and phosphoric acid were studied on a pyrogenic silica surface. Complete binding of phosphoric acid with the surface was observed as a result of thermal vacuum treatment. Oxidation‐reduction disproportion reactions in the samples containing phosphorus acid resulted in removal of molecular phosphorus in two stages which were attributed to disproportion of phosphorus atoms in the surface monolayer (high‐temperature stage) and in the bulk layers (low‐temperature s

ISSN:0951-4198    

DOI:10.1002/rcm.1290090708

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractAn ion microprobe unit was used to study silver isotope ratios in gold‐bearing ores. It was found that for ores formed under high‐temperature conditions the light isotope107Ag is enriched. Low‐temperature deposits are enriched in the heavy isotope

ISSN:0951-4198    

DOI:10.1002/rcm.1290090709

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractThe biologically active systems were synthesized by adsorption of vitamin B12, glucose and raffinose on an ultrafine oxide surface and studied by means of thermal analysis and temperature‐programmed mass spectrometry. It is shown that adsorption of cyanocobalamine (B12) on the silica surface transformed the propionamide group to a weakly bound form. The role of the charged cobalt atom and of the propionamide and benzimide groups in the adsorption mechanism is discussed. Experimental data were obtained confirming the stable adsorption of glucose and raffinose on an ultrafine pyrogenic silica surface modified by amino group

ISSN:0951-4198    

DOI:10.1002/rcm.1290090710

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractThe peculiarities of the temperature‐programmed mass spectrometry (TPDMS) experimental technique are discussed with reference to studies of biologically active molecules absorbed on ultrafine oxide surfaces. Simple theoretical models are presented in order to allow an approximate analytical treatment of TPDMS dat

ISSN:0951-4198    

DOI:10.1002/rcm.1290090711

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY