Fast Atom Bombardment Conditions Research Articles

Synthesis and mass spectrometric fragmentation pattern of 6-(4-chlorophenyl)-N-aryl-4-(trichloromethyl)-4H-1,3,5-oxadiazin-2-amines

Abstract The mass spectrometric fragmentation of 6-(4-chlorophenyl)-N-aryl-4-(trichloromethyl)-4H-1,3,5-oxadiazin-2-amines was studied under fast-atom bombardment (FAB) conditions. To simplify the interpretation of the mass spectra, a number of new 4H-1,3,5-oxadiazine derivatives containing polyisotopic elements (Cl and Br) in the arylamine substituent were synthesized. It was shown that fragmentation occurs in two main patterns.

Fast-atom bombardment mass spectra of some pentapeptides related to natural enkephalins.

The mass spectral features of four diastereoisomeric pairs of peptides related to the enkephalins recorded under fast-atom bombardment conditions are presented and shown to provide evidence of molecular weight and amino acid content and sequence.

Cooperative effect of factors governing molecular ion yields in desorption/ionization mass spectrometry

Factors governing the molecular ion yields of amino acids and peptides have been studied using fast atom bombardment (FAB) and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) in positive-ion mode. The ion yields of protonated amino acids under FAB conditions are dependent on proton affinity (PA), hydrophobicity, and aromaticity of amino acids. Both PA and hydrophobicity contribute to an increase in the ion yields, while aromaticity contributes to a decrease. In MALDI, the ion yields increase linearly with the increase of PA of amino acids with the exception of lysine. In both FAB and MALDI experiments with peptides, the presence of arginine residues is essential for producing abundant protonated peptides. In FAB, the presence of aliphatic and hydrophobic amino acids (leucine and isoleucine) increases the ion yields of protonated peptides, while some hydrophilic amino acids (aspartic acid and asparagines) decrease the ion yields. The presence of two or more arginine residues does not give higher ion yields in FAB. In MALDI, the presence of aromatic amino acids (phenylalanine and tyrosine) enhances the signals for protonated peptides. Thus, physicochemical factors of individual amino acids cooperatively affect the ion yields of protonated amino acids and peptides. These factors governing the ion yields in FAB and MALDI affect two processes, desorption and ionization, that can be considered independently.

Unprecedented Matrix-Induced Reduction of Flavins Observed Under FAB and MALDI Conditions

Flavin-derived compounds such as riboflavin, riboflavin 5-phosphate (flavin mononucleotide, FMN) and flavin-adenine dinucleotide (FAD), under matrix-assisted laser desorption ionization (MALDI) and fast atom bombardment (FAB) conditions produce unprecedented reduced species that can be attributed to [M+2H]+. and [M+3H]+ in addition to the anticipated [M+H]+ ions. On the other hand, electrospray ionization (ESI) conditions generate only the expected [M+H]+ as the sole molecular-related ion. A protonation from the matrix accompanied by a concomitant electron transfer, rather than the transfer of hydrogen atom(s), [H. of CH groups], is proposed to explain the observed reduction process. The reduction site expands to N(1)=C(10a)-C(4a)=N(5), a 1,4-diaza-1,3-butadiene system, in the isoalloxazine ring, resembling the behavior of prosthetic groups of aerobic dehydrogenases. Interestingly, CID-MS / MS of most abundant molecular-related ions generated by the FAB and ESI modes, namely [M+2H]+. for FAB and [M+H]+ for ESI, produce the identical even-electron fragment ion of isoalloxazine moiety, indicating a radical loss vs. the evenelectron molecule loss from the individual precursor ions. The observed phenomena are compared with those previously reported for FABMS, thermospray mass spectrometry (TSPMS) and ESIMS. Keywords: Matrix-Induced Reduction, Flavins, thermospray, prosthetic groups, aerobic dehydrogenases

Mass spectral fragmentation of (S,S)-2-substituted 4,4-diphenyl-3,1-oxazabicyclo[3.3.0]octanes: ring contraction of pyrrolidine and 1,3-oxazolidine in mass spectrometry.

The mass spectral behaviour of (S,S)-2-substituted 4,4-diphenyl-3,1-oxazabicyclo[3.3.0]octanes has been studied with the aid of mass-analyzed ion kinetic energy spectrometry and accurate mass measurements under fast atom bombardment (FAB) and electron impact (EI) ionization conditions. Under FAB ionization, all compounds show a tendency to form protonated aldehyde or benzophenone ions and to form protonated 1-azabicyclo[3.1.0]hexane ions, which can further lose an ethylene or cyclopropane from the pyrrolidine ring to produce protonated 1-azabicyclo[1.1.0]butane ions and 3H-azirine ions, respectively. Under EI ionization, a similar fragmentation to that under FAB ionization was observed. The title compounds also show a tendency to yield oxirane ions and oxirenium ions by loss of pyrrolidine and pyrrolidine plus H. Ring contractions of 1,3-oxazolidine by loss of an aldehyde or ketone and of pyrrolidine by loss of an ethylene or cyclopropane were observed under both FAB and EI ionization conditions.

Discrimination between pentose oligosaccharides containing D-xylopyranose or L-arabinofuranose as non-reducing terminal residue using fast atom bombardment mass spectrometry.

Collisional-induced dissociation (CID) mass spectra of the [M + H](+) and [M - H](-) ions obtained under fast atom bombardment conditions of a number of methyl glycoside di-, tri- and tetrasaccharides, containing D-xylopyranosyl and/or L-arabinofuranosyl residues at the non-reducing terminus, do not provide information about their ring size. This information could only be obtained from a careful comparison of the intensity ratio of the [M + Na - 90](+) and [M + Na - 104](+) ions ((0,2)X(t)/(1,5)X(t)) in the high-energy CID spectra of the sodium-cationized di-, tri- and probably also tetrasaccharide compounds.

Stability of 1-naphthalenediazonium ion in solution. Complexation and decomposition of 1-naphthalene- diazonium tetrafluoroborate in the presence of crown ethers and acyclic polyethers in 1,2-dichloroethane and the gas phase under fast atom bombardment conditions

The effects of solvent, temperature and pH on the rate of decomposition of uncomplexed 1-naphthalenediazonium tetrafluoroborate were studied by UV spectrometry. The complexation of the 1-naphthalenediazonium ion with crown ethers containing 4–10 oxygen atoms and some acyclic polyethers was detected and characterized in the gas phase by fast atom bombardment mass spectrometry (FAB-MS). In addition, the host–guest complexation and the kinetics of the thermal dediazoniation of 1-naphthalenediazonium ion in the presence of four crown ethers and two acyclic polyethers were studied in 1,2-dichloroethane (DCE) solution at 40 °C by UV spectrometry. All hosts, except 12-crown-4, formed 1:1 complexes under FAB conditions. The values of the thermodynamic stability K and the stabilizing ability of the complexation (k2/k1) in DCE were calculated from the kinetic data. The thermodynamic and kinetic stabilities were observed to be greater for the inclusion complex of the­1-naphthalenediazonium ion formed with crown ethers containing at least six oxygen atoms than for the non-spesific adduct formation formed with 15-crown-5. This was also true for tetraglyme, whose chain is too short to be capable of being fully wrapped around the diazonium group as in the complex of PEG 1000. Crown ethers with seven oxygen atoms are the strongest complexing agents for all the aromatic diazonium ions studied, for the 1-naphthal-enediazonium ion investigated here and for arenediazonium ions examined earlier. The values of the activation enthalpy ΔH≠ for the thermal dediazoniation of the uncomplexed salt in both the acidic aqueous solution and DCE were observed to be high, and the corresponding values of activation entropy ΔS ≠ were clearly positive. The results are consistent with a heterolytic SN1-like mechanism involving the decomposition of the uncomplexed and complexed 1-naphthalenediazonium ion into a highly reactive naphthyl cation, followed by fast product-determining reactions with nucleophiles to give the products. Copyright © 2000 John Wiley & Sons, Ltd.

Production of doubly charged clusters (H 2O) n · Ba 2+ and (H 2O) n · Ca 2+ under low temperature fast atom bombardment conditions

Production of doubly charged ions of alkaline earth metals Ba 2+ and Ca 2+ and their doubly charged clusters with water molecules (H 2O) n · Ba 2+, (H 2O) n · Ca 2+ ( n = 1, 2, 3) by means of low temperature fast atom bombardment technique is observed in the case of crystalline hydrates of BaCl 2 and CaCl 2 salts, formed during freezing of water-salt solutions. Reasons for a possibility of production of the doubly charged species in the case of the two indicated salts and their absence in the case of chlorides of some other divalent metals (Mg, Mn, Co, Cu, Zn) are discussed. As to singly charged secondary ions Me +, MeCl +, MeOH +, [(H 2O) n · MeCl] +, [(H 2O) n · MeOH] + (where Me is metal), high efficiency of their production from crystalline hydrates was observed and possible explanation of the phenomenon is suggested.

Evidence of gold-gold intra- and intermolecular interactions gained by laser desorption/ionisation and fast atom bombardment mass spectrometry in the study of some gold(I) coordination compounds

The mass spectrometric behaviour of some two-coordinated linear gold(I) complexes has been studied by fast atom bombardment (FAB) and laser desorption/ionisation (LDI) methods. The results obtained demonstrate some interesting aspects of Au-Au interactions. The detection under FAB conditions of Au(n)(+) clusters, in particular of Au(3)(+) species, can be rationalised by the presence of significant intramolecular Au-Au interactions, while the formation under LDI conditions of Au(n)(+) clusters can be considered indicative of Au(ellipsis)Au intermolecular interactions present in the solid state. Copyright 2000 John Wiley & Sons, Ltd.

Structural characterization of lichenysin A components by fast atom bombardment tandem mass spectrometry

The structural characterization of the cyclic lipoheptapeptide surfactant lichenysin A components, produced by Bacillus licheniformis strains via the non-ribosomal pathway on a corresponding peptide synthetase, was carried out using a tandem mass spectrometry (MS/MS) under fast atom bombardment (FAB) conditions. Based on the analysis of the collision-induced fragment-ion spectrum of the single charged molecular ions of both native and partially hydrolyzed forms of lipopeptide, a new general structure of lichenysin A components was elucidated. It varies from previously proposed structure by having in the peptide portion of lipopeptide the l-Gln-1 and l-Asp-5 residues instead of l-Glu-1 and l-Asn-5. The verified chemical structure of lichenysin A was found to be reflected in the structural organization of the corresponding lichenysin A synthetase, LchA, described recently.

Reductive degradation of O-acyl oximes under fast-atom bombardment conditions

A degradation phenomenon of O-acyl oximes under fast-atom bombardment (FAB) conditions is described from the point of view of reactivity with the liquid matrix and irradiation time with the xenon neutral beam. Mass spectra of O-acyl oximes were compared with those of the free oxime and hydroxylamine as model compounds, by using two different matrices, m-nitrobenzyl alcohol and DTT/TG12 (a 1 : 2 mixture of dithiothreitol and thioglycerol). A characteristic fragment ion was observed in the FAB mass spectra of O-acyl oximes and a free oxime only when DTT/TG12 was used. Collision-activated dissociation (CAD) was used to search for the origin and to confirm the structure of the characteristic fragment ion. The CAD spectra of the molecular-related ions, [M – H] + ,M +• and [M + H] + , demonstrated that this characteristic fragment ion was not derived from any of these precursor ions. The CAD spectra of the characteristic fragment ion, which originated from O-acyl oximes, were very similar to those from free oximes and these results indicated that the fragment ion had the same structure. It was concluded that the degradation, under FAB conditions, was caused by a reductive reaction of the oxime moiety (–O–N=C<) in O-acyl oximes regardless of its acyl moiety and that the degradation was initiated by the thiol group(s) in the matrix. The abundance of the ion originating from reductive degradation increased with increasing irradiation time with the xenon neutral beam.

Host-guest complexation of imine-type meta-bridged bis(benzo crown ether)s with alkali cations in the gas phase under fast atom bombardment conditions

The complexation of a series of bis(benzo crown ether)s of variable ring size and length of the linking chain with Na+, K+ and Cs+ was studied in the gas phase by fast atom bombardment mass spectrometry in nitrobenzyl alcohol/glycerol as a matrix. Both 2:1 (conventionally within the cavity of the crown ether units) and 1:1 complexes (a sandwich-like structure) were found depending on the cavity size of the crown units, the outer diameter of the complexing cations and the length and flexibility of the linking chain. © 1998 John Wiley & Sons, Ltd.

Mass spectrometry study on five‐substituted pyrroles and the related N‐methylene‐ 1,3,4‐thiodiazoles

Electron impact mass spectra of nine new substituted pyrroles are reported. Apart from compounds 1a and 1b, the other seven compounds produce R1--Ph--C≡O+ ions as base peaks. Except for compounds 2a–c, each compound may produce [M−EtOH]∔, [M−OEt]+ and other fragment ions. The proposed fragmentation mechanisms of the six new compounds giving M∔ ions have been supported by mass analysed ion kinetic energy spectrometry and accurate mass data. No molecular ion peaks of compounds 2a–c are observed under electron impact conditions. However, very intense protonated molecule peaks of compounds 2a–c were observed under fast atom bombardment conditions together with [M+H − EtOH]+ ions. By D-exchange experiments, it was verified that the proton is localized on the N atom between the carbonyl and thiocarbonyl groups during the formation of protonated molecules. © 1998 John Wiley & Sons, Ltd.

Ionization Efficiency from Matrix Surface Bombarded with Xe,Ar, and He Beams.

The ionization efficiency under fast atom bombardment conditions with liquid matrix have been studied. The dependence of fast atoms, Xe, Ar, and He, for the ionization efficiency from the surface of matrix solution bombarded with 6 keV atom beams has been rationalized from the standpoint of elastic/inelastic collisions between a fast atom and a matrix molecule in the surface layer. A relationship between ionization efficiency and atomic mass, which was formulated by a collision theory, predicted a tendency that the efficiency approaches asymptotically to a finite value with increasing atomic mass. The curves for the ionization efficiency versus atomic mass, obtained by using a few compounds, were in agreement with the theoretical prediction in the tendency.

The behaviour of [Pt(η3-allyl)XP(C6H5)3] complexes in electrospray ionization conditions compared with those achieved by other ionization methods

Three Pt(II) η3-allylic compounds, [Pt(η3-allyl)XP(C6H5)3] (X = Cl, Br, I) have been studied under electrospray ionization (ESI) conditions. Unexpected behaviour, such as the complete lack of either [M]+. or [MH]+ ions, the formation of complexes with the solvent and bis-triphenylphosphino-containing species, was observed. To rationalize such results, a series of parallel measurements on the same compounds have been performed under electron impact, fast-atom bombardment and field ionization conditions. The data so obtained suggest that molecular species are not produced by ESI, probably due to the action of strong electric fields and collisionally induced decompositions occurring in different regions of the instrument. Complexes with the solvent originate through gas-phase ion–molecule reactions, while the bis-triphenylphosphino-containing species are formed by reaction of ions with triphenylphosphine formed by thermal decomposition inside the heated capillary line, just after the electrospray ionization source. © 1997 John Wiley & Sons, Ltd.

Investigation of beam-induced reactions occurring under fast-atom bombardment conditions between triethanolamine and various phospholipids

The generation of adduct ions when using a triethanolamine (TEA) matrix under conditions of fast-atom bombardment has been investigated. In particular, phospholipids containing a free amino group react in the TEA matrix to form abundant adduct ions 26 and 42 mass units higher than the analyte pseudomolecular ions. The identity of these adduct ions was investigated using specific phosphatidylethanolamines and phosphatidylserine as well as 2-aminoethyldihydrogenphosphate and 2-aminoethylmonomethylphosphate as model compounds. Evidence obtained from positive- and negative-ion high-energy collision-induced dissociation tandem mass spectra, high resolution mass spectra, deuterium labelling and experiments using diethanolamine/TEA mixtures revealed that the intensities of the adduct ions are dependent on the percentage of TEA in the matrix and on the polarity of the analyte. The nature of the adduct ions is best reflected by a structure in which a hydrogen atom of the free amino group is substituted by a vinyl (+26) or by an acetyl (+42) group. A mechanism for the adduct ion formation is proposed. © 1997 John Wiley & Sons, Ltd.

Origin of clusters. II. Distinction of two different processes of formation of mixed metal/water clusters under low-temperature fast atom bombardment

The preparation of frozen samples, in which the heterogeneous structures differ on a scale comparable to the dimensions of the zone excited by a single bombarding particle, has permitted two different processes of formation of mixed metal/water clusters under fast atom bombardment conditions to be distinguished. Sandwich-like structures, in which sodium ions were

Mass Spectrometric Behavior of 5-S-Cysteinyldopa and Structurally Related Phenolic Compounds. Fragmentation Susceptibility of the Alkylthioether Bond Under Electron Impact and Fast Atom Bombardment Conditions

The marked proclivity of 5-S-cysteinyldopa (1) and related phenolic alkylthioethers to undergo UV-induced desulfurization via primary photohomolytic cleavage of the CH 2 -S bond prompted an investigation of the mass spectrometric behavior of these compounds with a view to obtaining information on the intrinsic susceptibility to dissociation of the alkylthioether bond under non-irradiative conditions. Dealkylative fission of the carbon-sulfur bond was found to be an important dissociative channel in the fragmentation patterns of 1 and related compounds, including cysteinylhydroquinone (2), 4-S-cysteaminylphenol (3) and 4-S-cysteaminylcatechol (4) under electron impact conditions. The mode of fission and relative susceptibility of the CH 2 -S bond were, however, profoundly different in cysteaminyl vs. cysteinyl compounds. In particular, the former showed a marked tendency to undergo simple homolytic fission, whereas in the latter dealkylative C-S bond cleavage occurred largely via an intramolecular rearrangement mechanism, and proved highly sensitive to protonation-induced effects, as evidenced in fast atom bombardment experiments. Desulfurization processes with neat loss of the alkylthio residue, like those occurring upon UV irradiation, were virtually absent in the fragmentation patterns of 3 and 4, and provided only a minor contribution to those of 1 and 2. These and other data reported open fresh prospects for future studies on the chemistry and mass spectrometric behavior of 1 and structurally related phenolic compounds of biological relevance.

Mass Spectrometric Behavior of 5-S-Cysteinyldopa and Structurally Related Phenolic Compounds. Fragmentation Susceptibility of the Alkylthioether Bond Under Electron Impact and Fast Atom Bombardment Conditions

Mass Spectrometric Behavior of 5-S-Cysteinyldopa and Structurally Related Phenolic Compounds. Fragmentation Susceptibility of the Alkylthioether Bond Under Electron Impact and Fast Atom Bombardment Conditions

Mass Spectrometric Investigation of 5,6- and 5,7-Dihydroxytryptamines and their Biological Precursors

A mass spectrometric investigation of tryptamine, 5-hydroxytryptamine and 5,6- and 5,7-dihydroxytryptamine was carried out using two different ionization methods, metastable ion studies and accurate mass measurements. In electron impact (EI) conditions, a series of decomposition processes, clearly related to the structure of neutral molecules, was evidenced, although 5,7-dihydroxytryptamine showed severe problems related to its vaporization. The characterization of the two isomeric compounds was possible only by ion trap mass spectrometry. In fast atom bombardment conditions, decomposition pathways analogous to those observed in EI conditions were detected, and new decomposition channels due to NH 3 and NH 2 loss indicated that protonation takes place on the primary amine nitrogen atom.