摘要:

AbstractA pneumatically assisted electrospray liquid chromatography/mass spectrometry interface has been modified for use with open‐tubular supercritical fluid chromatography (SFC). The modified interface houses the SFC flow restrictor within the spray device. A sheath‐flow liquid of methanol or methanol/water containing ammonium acetate flows coaxially to the restrictor. The addition of the sheath‐flow liquid results in the ionization of analytes known to be in a neutral charge state during the chromatographic separation. The sheath‐flow liquid also allows for the independent operation of the chromatograph and the mass spectrometer. Both could be operated under optimum conditions. The operation of the interface was optimized using a solution of poly(dimethylsiloxane) in CO2introduced by continuous infusion. We also report the application of the modified instrument to samples containing amines and propoxylated a

ISSN:0951-4198    

DOI:10.1002/rcm.1290091202

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractA matrix‐assisted laser desorption/ionization (MALDI) mass spectrometric mapping strategy for the identification and characterization of isolated and purified proteins is described. The method, which employs the combined usage of a new site‐specific enzymeAsparaginyl endopeptidase(Asn‐EP) for proteolysis, and MALDI for subsequent mass analysis, is capable of rapidly and sensitively examining the components of complex mixtures without any chromatographic or electrophoretic separation steps. Subpicomole sample quantities typically suffice to permit the confirmation of deduced primary structures and/or the identification of possible post‐translational modifications. The data obtained should also prove useful for mass matching and sequence homology searching of computerised protein sequence data bases of known p

ISSN:0951-4198    

DOI:10.1002/rcm.1290091203

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractThe tris(acetylacetonate) (L3) and tris(1,1,1‐trifluoromethyl‐2,4‐pentanedionate) (L′3) complexes of transition metals V, Cr, Mn, Fe, Co, Ru and Os in their +3 oxidation states were studied under fast‐atom bombardment (FAB) conditions using 3‐nitrobenzyl alcohol as a matrix. All complexes showed the formation of molecular ion and protonated molecules [ML2]+and [ML′2]+are the most abundant ions in the spectra of all the metal acetylacetonates (L) and trifluoroacetylacetonates (L′) studied. Interaction of matrix with metal complexes and polynuclear metal complexes led to the formation of polynuclear species with significant abundance especially for manganese and iron complexes. Formation of these metal ions was observed with relative intensities from 3–30%. Ions corresponding to ligand‐exchange reactions were observed with moderate to high abundance in all metal complexes studied except those of ruthenium and osmium. Experiments carried out with a split FAB probe tip suggested ligand–ligand exchange reactions were not due to gas‐phase reactions but only due to solution‐phase exchanges. Osmium and ruthenium complexes do not yield polynuclear species or ions due to matrix clustering. Instead they show neutral ligand losses an

ISSN:0951-4198    

DOI:10.1002/rcm.1290091204

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractNatural taurine is an essential constituent of formula milk for infants and, because of the inferior nutritional value (δ), of synthetic forms, it is important to discriminate between these and taurines derived from a natural source. In this study we evaluated the ability of a method to make this distinction; it consisted of determination of the taurine13C/12C ratio by means of a precision automated continuous flow mass spectrometric apparatus. This method was found to provide a powerful analytical tool for this purpose

ISSN:0951-4198    

DOI:10.1002/rcm.1290091205

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractPolyphosphoinositides (PIP) and (PIP2) show prominent negative singly and doubly charged deprotonated molecules in electrospray mass spectrometry. These ions can be used for quantification of PIP and PIP2in the low picomole range, without prior chromatographic separation, using selected ion monitoring and consecutive measurements of the signals from the deprotonated singly charged molecules. The dose response curves for both compounds are linear. In a complex matrix consisting of polar lipids (Folch extract) PIP and PIP2monitored atm/z965.4 and 1045.5 (stearoyl and arachidonoyl) were determined in the low picomole range, at a flow rate of 100 μL/min. Collision‐induced decomposition of PIP and PIP2using a mixture of xenon and argon at 25 eV afforded identical high mass ions formed by loss of a molecule of water from PIP and a phosphate group and a molecule of water from PIP2. The results indicate that polyphosphoinositides, and biologically relevant changes in their concentrations, can be quantified directly in cells and cellular membranes by selected‐ion monitoring with electrospray mass spectrom

ISSN:0951-4198    

DOI:10.1002/rcm.1290091206

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractThe potential energy surface of n‐hexane radical cations is probed theoretically. The structures with low internal energies are characterized by extensive lengthening of one of the three innermost CC bonds. This CC bond stretch is induced by localization of the positive charge. For an elongated terminal CC bond we calculated an energy which is 0.4 eV higher than that for a stretched central CC bond. The n‐hexane geometries with several CC bonds stretched do not represent stationary points on the potential energy surface. Comparison with previous dissociative‐neutralization experiments of low‐internal‐energy n‐hexane ions shows that the fragmentation pathways reflect the two low

ISSN:0951-4198    

DOI:10.1002/rcm.1290091207

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractThe electron impact mass spectra of some newly synthesized heteropolycyclic bis‐carboxamides are discussed. The dominant peaks in all these spectra are formed by the cleavage of the CN bond on one side of the anilino group with the formation of a fragment ion C9H4OSCI+m/z195, as the base peak. Cleavage of the CN bond with charge retention on nitrogen leads to characteristic ions in some

ISSN:0951-4198    

DOI:10.1002/rcm.1290091208

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractThe mechanisms of the mass spectrometric fragmentation of two compounds, I (evoxine) and a new compound II (O‐methylcaureolol), were analyzed using mass‐analyzed ion kinetic energy spectrometry, and by verifying the elemental composition and structure of some important fragment ions by high‐resolution data. We discovered that the double bond in position 9,11 of the C ring of II may be diverted to position 7,8 of the B ring and that a typical retro‐Diels–Alder reactio

ISSN:0951-4198    

DOI:10.1002/rcm.1290091209

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractThe behaviour of three fluorinated acyclic nucleoside analogs has been examined under different ionization conditions, i.e. by electron ionization, fast‐atom bombardment and positive‐ion chemical ionization using methane, isobutane and ammonia as reactant gases. The protonated molecules have been studied by collisional spectroscopy. In general, protonation takes place on the functional groups exhibiting a proton affinity higher than that of the reactant species but some discrepancies are present. They have been explained by the presence ofquasiSHF structures implicating proton bridging between sulphur and fluorin

ISSN:0951-4198    

DOI:10.1002/rcm.1290091210

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractThe conformational properties ofRhodobacter capsulatuscytochromec2wild‐type and two site‐directed mutants (glycine 34 replaced by serine and proline 35 replaced by alanine) were characterized by their charge state distributions and hydrogen/deuterium (H/D) exchange properties monitored by electrospray ionization mass spectrometry. The results suggest the presence of structural perturbations in the mutated cytochromes, an observation that is in agreement with their decreased conformational stabilities. In addition, a fast enzymatic procedure was developed to identify regions for which the H‐bonding or solvent accessibility properties were perturbed by the mutations. In this procedure, deuterated peptides were separated and analysed by using liquid chromatography directly coupled to the electrospray ionization source in order to minimize the occurrence of back‐exchange during analysis. In the case of G34S, mutational effects were found for peptides 1–26, 38–51, 52–59 and 109–116, which in theRb. capsulatuscytochromec2structure correspond to extensive regions on the same side of the molecule as the proximal histidine, as well as part of the C‐terminal helix. In the case of P35A, mutational effects were found for peptides 1–26, 27–37, 38–51 and 52–59, which in theRb. capsulatuscytochromec2stucture correspond to extensive regions on the same side of the molecule as the proximal histidine. We show that the present set of mass spectrometric experiments is useful as an initial characterization of mutant conformational properties because the analyses require only nanomole quantities of protein and

ISSN:0951-4198    

DOI:10.1002/rcm.1290091211

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY