Negative-ion Fast-atom Bombardment Mass Spectra Research Articles

Negative-ion electrospray ionization tandem mass spectrometry of N-phosphoryl amino acids and dipeptides.

The negative-ions of N-phosphoryl amino acids were studied by electrospray ionization tandem mass spectrometry (ESI-MS/MS). The negative-ion ESI-MS/MS of N-phosphoryl amino acids showed characteristic fragmentation patterns different from those observed in the corresponding positive-ion ESI-MS/MS and negative-ion fast-atom bombardment mass spectra. For negative-ion ESI-MS/MS, a unique fragmentation from the N-terminal of N-phosphoryl amino acids or peptides containing a free beta-OH or CO(2)H group was observed to yield the characteristic fragment ion (RO)(2)P(O)O(-). The ease of the rearrangement depended on the position of the hydroxyl group in amino acids or peptides, and the N --> O rearrangement mechanism was proposed to involve the participation of the hydroxyl group. From previous solution-phase experiments and theoretical calculations, it was found that the beta-OH group was more active than gamma-OH, and the corresponding difference in negative-ion ESI-MS/MS was consistent with those previous findings.

Formation of (M-H)- Ions under Fast-atom Bombardment Conditions: Which is reflected, gas-phase or solution chemistry?

The formation of deprotonated molecules [M-H]- of Trolox having a carboxyl and a phenolic hydroxyl group and the derivatives, under fast-atom bombardment (FAB) conditions, has been examined from the viewpoint of proton-transfer reaction in gas-phase or solution. The negative-ion FAB mass spectra of the derivatives strongly suggested that deprotonation mainly occurs on the carboxyl group through the electrolytic dissociation in matrix solution. The use of higher proton acceptability matrices such as glycerol, pentamethylene glycol, and diethanolamine was favorable for the detection of [M-H]- ions of a Trolox methyl ester, while the use of lower proton acceptability matrices such as m-nitrobenzyl alcohol and dithiothreitol was unfavorable for the [M-H]- formation. While the result obtained suggested that the formation of [M-H]- ions reflects the gas-phase basicities of matrices used, the results from the negative-ion FAB mass spectra of the Trolox methyl ester and α-tocopherol suggested that the [M-H]- formation reflects solvation states such as hydrophobic and hydrophilic interactions between analyte and matrix molecules in matrix solution. The site of deprotonation of the compounds used has been examined by using collision-induced dissociation (CID) technique, and it was shown that the CID characteristics of [M-H]- ions depend markedly on the site of deprotonation. It was presumed, consequently, that the [M-H]- ion formation under FAB conditions is governed by gas-phase thermochemistry and/or solution chemistry according to the nature of analyte and matrix used.

Fast atom bombardment and high performance tandem mass spectrometry of platinum(II) oligodeoxyribonucleotide fragments

The antitumor drug cisplatin [ cis-diamminedichloroplatinum(II), cis-DDP] exerts its biological activity by binding to cellular DNA. In order to evaluate the utility of mass spectrometry as a possible new approach to investigate the number and type of Pt-DNA adducts in both mechanistic and clinical studies, a systematic survey of the fast atom bombardment (FAB) and high performance tandem mass spectrometry (MSMS) spectra of a series of well-defined adducts has been carried out. Included in the set of compounds were adducts between cisplatin or its trans isomer and oligodeoxyribonucleotides containing two to six bases, selected to represent all the known binding modes of cisplatin to DNA, and stable isotope-labeled ( 15N, 195Pt) complexes. In both positive- and negative-ion FAB mass spectra, all compounds yield ions corresponding to the singly-charged intact cluster, and to fragments that arise by loss of one or two ammine groups. The isotope ratio patterns of the clusters indicate that mixed species containing varying numbers of hydrogens are present. MS—MS spectra obtained after high energy (1–7keV) collisionally-induced dissociation (CID) have more extensive fragmentation. Two sets of product ions indicative of the Pt- binding site are consistently present; these correspond to Pt(NH 3) 0–2 (B x or y ) and Pt(NH 3) 0–2 (B x B y ), where B x and B y are the nucleobasis linked to Pt in the adduct. CID mass spectra recorded at 1 keV have additional product ions related to the nucleotide sequence.

Molecular species analysis of arachidonate containing glycerophosphocholines by tandem mass spectrometry

Carboxylate anions arising from collision-induced dissociation (CID) of the [M − 15] − ion produced by fast atom bombardment (FAB) of glycerophosphocholine (GPCho) were previously shown to be produced in an abundance ratio of 1:3 for the carboxylic acids esterified at sn - 1 and sn - 2, respectively. This observation has been confirmed in a series of 13 synthetic GPCho molecular species. A good correlation was found between the isomeric purity of GPCho molecular species as determined by negative-ion FAB/CID analysis and the isomeric purity of the sn - 2 fatty acid using a phospholipase A 2 assay. Negative-ion FAB mass spectra of several 1- O-alkyl-2-acyl-GPCho molecular species were found to be similar to those of diacyl GPCho. However, the CID spectra from the major high-mass ions are different from those of the diacyl species in that the [M − 15] − ion yields only one carboxylate anion and the [M − 86] − undergoes a neutral loss of the sn - 2 carboxylic acid as a major decomposition product. These reuslts suggest several rules useful for structural characterization of GPCho molecular species by negative-ion tandem mass spectrometry (MS/MS): (1) For diacyl species, the mass of the two carboxyl anions plus the mass of the GPCho backbone (minus a methyl group) must correspond to the mass of the [M − 15] anion; (2) for diacyl species there is a carboxylate anion ratio approximately 1:3 for the substituents at sn - 1 and sn - 2; and (3) for alkylether species, only one fatty acyl group is present, and the difference between the [M − 15] ion and the GPCho backbone (minus methyl) plus the fatty acyl group at sn - 2 corresponds to an alkylether substituent. (4) Assignment of ether-linked molecular species can be made from the [M − 86] − ion, which has a strong neutral loss of the sn - 2 fatty acid. Analysis of GPCho isolated from human neutrophils by total lipid extraction and normal-phase HPLC was carried out by negative-ion FAB and MS/MS. The major arachidonate-containing molecular species, which comprise only 5% of total GPCho, were identified by using precursor ion scans for the arachidonate anion, m/ z 303. Decomposition of identified precursor ions permitted the assignment of those molecular species of GPCho that contain arachidonate at sn - 2 and identification of the substituent at the sn - 1 position. These results were compared to previously identified molecular species from human neutrophils. Several minor arachidonate-containing molecular species were tentatively identified.

N-Formyl-2-aminoethanol as a matrix for fast atom bombardment mass spectrometry of non-polar biomolecules

N-Formyl-2-aminoethanol appears to be a very suitable matrix for the fast atom bombardment (FAB) mass spectrometry of many (bio)organic molecules. The best results so far have been obtained with compounds having a decreased hydrophilic character. These include (per)methylated oligosaccharides and peptides containing relatively many amino acids with non-polar side-chains. The positive and negative ion FAB mass spectra of these compounds show abundant [M + H] +, [M − H] − and sequence ions, while the ions resulting from the matrix do not dominate.

Degradation and isomerization of nileprost, 5-cyano-16-methyl-prostacyclin, in aqueous solution.

Nileprost is a new prostacyclin analogue stabilized by introduction of the cyano group at its 5-position. The acidic and alkaline degradation and the structure determination of the degradation products were investigated. The degradation of nileprost is very slow in comparison with that of prostacyclin. Although prostacyclin is easily decomposed to 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) through the hydrolysis of a vinyl ether moiety, nileprost gives little of such hydrolysis product but many isomers and dehydrates. The structures of the products were determined by high-performance liquid chromatography (HPLC), negative ion fast atom bombardment mass spectra (N-FABMS) and nuclear magnetic resonance (NMR) studies. It was found that the vinyl ether moiety of nileprost is converted from 5Z form to 5E form in both media, and that the omega-side chain also undergoes transfer of hydroxyl group or dehydration in acid medium. These results indicate that introduction of the cyano group into the 5-position of prostacyclin is extremely effective for the stabilization of the vinyl ether moiety. Furthermore, on the basis of the structural elucidation, the reaction mechanism of nileprost in both media was clarified.

Ligand Exchange in FAB Mass Spectrometry of Monomerie and Dimeric Corrinoids

Abstract In the Fast Atom Bombardment (FAB) mass spectra of monomeric and dimeric corrinoids, exchange of metal-bound ligands against matrix particles is observed which leads to pseudo molecular ions. Negative ion FAB mass spectra in particular, give distinct information on the intact molecular units.