摘要:

AbstractGlow discharge mass spectrometry (GDMS) is a mature, versatile technique for the direct determination of trace elements in a variety of materials. The technique is an extension of the earliest forms of mass spectrometry. Processes inherent to the glow discharge, namely cathodic sputtering coupled with Penning ionization, yield an ion population from which semi‐quantitative results can be directly obtained. Quantification in GDMS is achieved both through standard elemental mass spectrometric procedures and more innovative approaches. The analytical performance of GDMS compares favorably with competing elemental mass spectrometric methods and newer experiments use this ionization method for both molecular and elemental analysis. As with any analytical technique, the future of GDMS lies in improvements with respect to instrumental implementation and extension to new areas of application. If the method is to remain competitive, commercial GDMS systems must incorporate advances in mass spectrometric technology to increase analytical performance while decreasing the size, complexity and cost of the technique. Continued efforts to develop improved quantitation procedures are needed to provide greater accuracy. The method should continue to mature as sustained efforts demonstrate its utility in the solution of new and more varied problem

ISSN:1076-5174    

DOI:10.1002/jms.1190300802

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe calcium‐binding properties of parvalbumin and calmodulin were investigated by electrospray ionization mass spectrometry (ESI‐MS). The two calcium sites of parvalbumin were found to be strongly cooperative in binding Ca2+ion. Up to four calcium ions were found to bind to calmodulin at high calcium concentration levels. Strong cooperativity was detected between the third and fourth Ca2+binding sites of calmodulin (ordered by loading sequence). Strong interactions were also indicated between the two halves of the calmodulin molecule. Demetallation of the gas‐phase ions can occur during the desolvation process, especially for ESI of aqueous solutions. However, the ESI‐MS methodology has the potential to provide insight into the intricate processes involved in metal site communications for other metallop

ISSN:1076-5174    

DOI:10.1002/jms.1190300803

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe ionized geometric isomers maleic and fumaric acids ((Z)‐ and (E)‐ethenedicarboxylic acids) were studied by a variety of tandem mass spectrometric techniques. In agreement with much earlier work, the metastable ionized isomers do not reversibly interconvert. They do, however, have two dissociation channels, H2O and CO losses, for which common transition states are involved. Ionized maleic acid has one geometry‐specific dissociation, loss of CO2. Structures were assigned to all major fragment ions together with their heats of form

ISSN:1076-5174    

DOI:10.1002/jms.1190300804

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe negative‐ion collisionally induced dissociation fast atom bombardment mass spectra of sodium salts of monensins A and B, their 3‐O‐demethyl derivatives, laidlomycin and 26‐deoxylaidlomycin are reported. The nature of the R3substituent appears to be important for the formation of sodium‐containing product ions. Fragment ion series observed in the mass spectra of the [M − H]−ions of monensins are characterized by alkali metal retention. In contrast to monensins, the product ions observed in the corresponding spectra of laidlomycins are sodium free. The affinity of monensins to alkali metals is a useful feature that may be used for the structure determination of unknown monensins, their metabolites and derivates. The structure of a novel natural monensin was elucidated based on its mass spectromet

ISSN:1076-5174    

DOI:10.1002/jms.1190300805

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe relative non‐covalent binding behavior of two small molecule ligands to the tetrameric protein streptavidin was investigated by electrospray ionization mass spectrometry (ESI‐MS). An extendedm/zrange quadrupole mass spectrometer was employed to observe the intact multimeric form of the protein and to probe the relative stabilities of the tetrameric protein‐ ligand complexes in the gas phase. Various protein:ligand molar ratio concentrations and incubation times were studied for the ligands biotin (Kd≈ 10−15M) and iminobiotin (Kd≈ 10−7M), in combination with the adjustment of variables in the ESI atmosphere‐vacuum interface region. Positive‐ion ESI‐MS of a 1:7 molar ratio streptvidin–biotin sample produced peaks corresponding to the intact tetrameric complex (16+ to 14+ charge states) with four ligands binding to the active from of the protein. Only the expected specific non‐covalent complexes of four ligand molecules binding to the protein tetramer were detected, consistent with known solution behavior and without the appearance of any random aggregation. However, under identical interface conditions, complete iminobiotin binding to the protein was not observed, even when higher ligand concentrations, longer complexation times and gentler interface conditions were employed. The thermally induced dissociation (TID) of the non‐covalent complexes was studied by applying more severe conditions in the ESI interface region. In addition, observation of an intact streptavidin–biotinylated oligonucleotide non‐covalent complex (17– to 14– tetrameric charge states) by negative‐ion ESI‐MS atm/z4500–5000 is presented. The results show that the complexes observed in the mass spectrometer are representative of those that exist in solution, under the ESI conditions employed, and that the ability to observe such complexes is at least qualita

ISSN:1076-5174    

DOI:10.1002/jms.1190300806

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe kinetics of gas‐phase HD exchange reactions of a series of protonated amino acids and peptides with deuterium‐substituted alcohols (D2O, CH3OD, C2H5OD and 1‐C4H9OD) were studied in an external source Fourier transform mass spectrometer. The number of exchanges observed on the time‐scale of these experiments ranged from one to the total number of ‘labile’ substrate hydrogens, depending on the amino acid and the deuterating reagent. Exchange efficiencies,k/kADO, varied from<0.001 to 0.3. Within the series ROD, the reactivity increased with increasing size of the R group. For the amino acids with alkyl side‐chains, a roughly linear correlation of log(k/kADO) with proton affinity difference (ΔPA=PAof unprotonated substrate ‐PAof reagent) was observed. The amino acids lysine and histidine and the dipeptides alanylglycine and diglycine showed higher reactivity and greater tendency for multiple exchange, with a weaker dependence on ΔPA. The ability of a peptide and an alcohol to exchange efficiently even when ΔPAis larger is attributed to the occurrence of exchange within a cyclic hydrogen‐bonded complex, in which the deuterating agent forms a bridge between the site of protonation and a basic

ISSN:1076-5174    

DOI:10.1002/jms.1190300807

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractA combination of mass shifts arising from known structural variations of neutral precursors, and accurate mass measurements of key fragment tions, has led to a proposed systematization of the low‐energy fragmentation mechanisms for MH+ions of actinomycins. These rationalizations are used in a predictive manner to interpret fragment ion spectra, of unknown impurities in actinomycin standards, in terms of structure. Both the strengths and limitations of this approach are emphasized. This work has uncovered actinomycin variants in which one of the threonine residues is substituted by serine, a structural variation which does not appear to have been reported previousl

ISSN:1076-5174    

DOI:10.1002/jms.1190300808

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe fragmentation pathways of several substituted 1,4‐naphthoquinones have been studied by multi stage mass spectrometry. Methods for the recognition and identification of 1,4‐naphthoquinones and of substitution patterns on the naphthoquinone nucleus are outli

ISSN:1076-5174    

DOI:10.1002/jms.1190300809

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractAlkyl methylphosphonic acids (AMPA) are metabolites and primary hydrolysis products of the organophosphorus nerve agents listed in the Chemical Weapons Convention (CWC). Gas chromatography/negative‐ion chemical ionization mass spectrometry and tandem mass spectrometry (GC/NICI‐MS and GC/NICI‐MS/MS) were used for the determination of AMPA as their pentafluorobenzyl esters. Extremely high sensitivity was obtained and low attogram amounts could be detected by GC/NICI‐MS. Ion‐exchange chromatography was employed for selective isolation and enrichment of AMPA in serum, urine, water and soil samples. Collision‐induced dissociation (CID) of the single methylphosphonate anion peak from NICI of the pentafluorobenzyl ester produced fragment ions specific for the methylphosphonate structure, allowing positive identification of AMPA. CID conditions optimized for structure information and for sensitivity were investigated. The improved selectivity of GC/MS/MS allows the detection of femtogram amounts of AMPA in samples where chemical background inhibits detecti

ISSN:1076-5174    

DOI:10.1002/jms.1190300810

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractConsistent with experimental observations, high‐levelab initiocalculations, at the G2(MP2) level of theory, predict that the XCCY2+(X, Y = O, S and NH) dications are remarkably stable species in the gas phase. OCCS2+, SCCS2+, HNCCO2+, HNCCS2+and HNCCNH2+are calculated to be thermodynamically stable species, whereas OCCO2+is predicted to lie in a deep potential well, separated from exothermic CC cleavage by a large barrier. All the doubly charged species are calculated to have a linear skeleton. Despite the inherent strong Coulombic repulsion, these species are characterized by short CX or CY triple bonds. Vertical and adiabatic ionization energies of the XCCY+·monocations and the heats of formation of the resulting dications are reported. There are remarkable changes in the structures and stability ordering of isomers on going from the XCCY neutrals to the XCCY+·monocations and to the XCCY2+dications. The rationalization of these results is

ISSN:1076-5174    

DOI:10.1002/jms.1190300811

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY