Linked Scan Technique Research Articles

Electron ionization and electrospray ionization mass spectrometric study of a series of isomeric N‐chloro(or bromo)benzyl‐substituted (E)‐2′(3′‐ or 4′)‐hydroxy‐4‐stilbazole halides

The electron ionization (EI) mass spectra and electrospray ionization (ESI) mass spectra of a series of isomeric N-chlorobenzyl- and N-bromobenzyl-substituted (E)-2'(3' or 4')-hydroxy-4-stilbazole chlorides and bromides (1-12) were recorded. The fragmentation pathways of all of the compounds and the characteristic fragment ions formed by EI-MS were studied by means of B/E and B(2)/E constant linked-scanning techniques. The formation of ions originating from preionization reactions, characteristic of quaternary halides under EI-MS conditions, such as the elimination of chloro- or bromobenzyl halides, dehydrohalogenation or substitution reactions, is explained. As soft ionization methods cause no such degradation reactions, the ESI-MS spectra of the studied compounds were also obtained for comparison. We thus demonstrated the applicability of EI-MS even in cases when preionization takes place, as long as such secondary processes are properly accounted for.

Mass spectra of aminoacyl adenylate pentacoordinated phosphorus compounds

Aminoacyl adenylate pentacoordinated phosphorus compounds were analyzed by field desorption (FD) and fast atom bombardment (FAB) mass spectrometries, together with the B/E linked scan technique, and their mass spectral fragmentation pathways were investigated. For the five bonds (one P-N bond, three P-O bonds and one mixed anhydride bond P-O-CO), the cleavage usually occurred more on the P-N bond, the mixed anhydride bond and the O-C bond adjacent to the P-O bond, and less on the P-O bond. Ion YH(+), corresponding to water loss from protonated 2',3'-O-isopropylidene-adenosine, was the base peak. The results reflect the structural characteristics of aminoacyl adenylate pentacoordinated phosphorus compounds. Copyright 1999 John Wiley & Sons, Ltd.

Mechanistic Studies of Diastereomeric Nickel(II)N-Glycoside Complexes Using Tandem Mass Spectrometry

Ni(II) N-glycoside complexes of four diastereomeric monosaccharides were synthesized and analyzed by fast atom bombardment-mass spectrometry. The average kinetic energy release (KER) associated with the formation of a C2H4O2 neutral loss was indicative of stereochemical differences in the coordinated monosaccharide. Isotopic labeling studies and various linked scanning techniques were undertaken, suggesting multiple dissociation pathways from different reacting configurations, leading to the formation of isomeric [M-C2H4O2] product ions. Additionally, computational studies predict the presence of large structural differences between complexes possessing axial or equatorial C-2 substituents.

Structural heterogeneity of the sialic-acid-containing oligosaccharides from the lipopolysaccharide of Hafnia alvei strain 2 as detected by FABMS studies

The structure of four oligosaccharide fractions from the Hafnia alvei strain 2 lipopolysaccharide (LPS) have been assigned by FABMS. This approach corroborates data previously established by NMR spectroscopy for the major oligosaccharides in these fractions [A. Gamian, E. Romanowska, U. Dabrowski, J. Dabrowski, Biochemistry 30 (1991) 5032–5038; E. Katzenellenbogen, A. Gamian, E. Romanowska, U. Dabrowski, J. Dabrowski, Biochem. Biophys. Res. Commun. 194 (1993) 1058–1064; N. Ravenscroft, A. Gamian, E. Romanowska, Eur. J. Biochem. 227 (1995) 889–896]. In addition, the MS/MS with B/E linked scan technique allowed the detection of an additional oligosaccharide with the structure: lacking the branched O-6 linked glucopyranose residue at the 3-linked Gal unit, which indicates a structural heterogeneity for the major oligosaccharide fraction.

Self-assembly of N,O-bis(trimethylsilyl)amino acids to peptides mediated byo-phenylene phosphorochloridate identified by fast atom bombardment mass spectrometry

The self assembly of N,O-bis(trimethylsilyl)amino acids to form peptides, mediated by o-phenylene phosphorochloridate, was investigated by positive ion fast atom bombardment and B/E linked-scan techniques without isolation and purification prior to analysis. The expected results were confirmed by considering the fragmentation regularity of peptides. © 1998 John Wiley & Sons, Ltd.

Mass Spectrometric Study of Some Organotellurium(IV) Compounds

A series of tetracoordinated organotellurium(IV) compounds with potential immunomodulating properties were studied mass spectrometrically using high-resolution positive ion desorption chemical ionization and constant B/E and B 2 /E linked-scanning techniques. The nature of the organic ligand bonded to the Te(IV) has a major influence on the mass spectral behavior of these compounds. When only monodentate ligands -OR are bonded to the Te(IV), no molecular or protonated molecular ion appears in the spectrum, although polynuclear species are present. When the compounds contain bis-bidentate ligands of the type -ORO-, the protonated molecular ion becomes the base peak and the polynuclear species are not present.

Analysis of Functional Groups of Porphyrins by Collision-Induced Dissociation Mass Spectrometry/Mass Spectrometry.

Collision-induced dissociation mass spectrometry/mass spectrometry (CID-MS/MS) was effective for estimating the substituent groups of porphyrin. The substituents of the porphyrin plane, which form the pathway for an oxygen-binding reaction, are essential for its oxygen-binding affinity. The CID-MS/MS of 5,10,15-tris(o-pivalamidophen-yl)monoaminoporphyrinatocobalt and 5,10,15,20-tetrakis(o-pivalamidophenyl)porphyrinatocopper was measured, and their fragmentations were studied using B/E-constant and B(1—E)1/2E-constant linked-scan techniques. These CID-MS/MS spectra clearly show that the substituent group represents the eliminations of the alkyl and acyl radicals from the molecular ions. Thus, the CID-MS/MS technique has been proven to be useful for characterizing porphyrin substituents.

Identification of rat faecal metabolites of ebastine by B/E linked scanning liquid secondary ion mass spectrometry.

The identification of rat faecal metabolites of a new antihistaminic agent, ebastine, 4'-tert-butyl-4-[4-(diphenylmethoxy)piperidino]butyrophenone, is presented. After oral administration of (14C)ebastine (20 mg kg-1) to rats, 84% of the radioactive dose was excreted in the 24 h faeces. Unchanged drug and five metabolites were isolated from the faeces by thin-layer chromatography and solid-phase extraction, and their structures were identified by liquid secondary ion mass spectrometry using the B/E linked scanning technique. The main metabolic pathways were oxidation of a terminal methyl group to give the hydroxymethyl and carboxyl derivatives, and hydroxylation of a phenyl ring in the diphenylmethoxy moiety. In addition to the oxidative mechanism, metabolism of ebastine involved sulphate conjugation. It is noteworthy that M-4, having both phenolic and alcoholic hydroxyl groups, was sulphated selectively in the latter position.

Fragmentation of Silaspiroalkanes in EI Mass Spectrometry.

The fragmentations of six silaspiroalkanes combined with four-, five-, and six-membered rings in EI mass spectrometry have been studied by a B/E linked scanning technique and an ab initio MO method. The main fragmentation process from the molecular ion is the consecutive losses of two ethylene molecules which occur via the cleavage of an Si-C bond in each ring of silaspiroalkanes. From the ab initio MO calculation, we found that the initial bond fission occurred in an Si-C bond of the molecular ion. At that time, the cleavage of an Si-C bond occurs in the smaller ring more easily than in the larger one, since the strain on the smaller ring is larger. We found the metastable decomposition due to a CH3 loss from the molecular ions of 4-silaspiro[3.5]nonane, 5-silaspiro[4.4]nonane, and 4-silaspiro[3.4]octane.

Trimethylsilyl group migration in the mass spectra of trimethylsilyl ethers of cholesterol oxidation products. Product ion characterization by linked-scan tandem mass spectrometry

Loss of the A ring in the electron-impact mass spectra of the trimethylsilyl (TMS) derivatives of several cholesterol oxidation products is accompanied by intramolecular migration of the 3- O-TMS group to the charge-retaining portion of the molecule. Linked-scan techniques (B/E and B 2/E) were used to establish the fragmentation processes leading to the formation of the rearrangement ion. The TMS group appears to migrate to heteroatomic sites in the 5-, 6-, or 7-positions of the B ring. This structural assignment is supported by isotopic labeling studies and collision-induced dissociation of the resulting product ion.

Ligand effects on the fragmentation of ion–molecule complexes of transition-metal ions with amines

The dissociations of a series of metastable RNH2–CoCl+ complex ions (R = alkyl) have been studied using B/E linked scan techniques. These reactions were compared with those of corresponding RNH2–Co+ ions. Ligand effects on the metal-ion reacvity and ligand–ligand coupling are presented.

Fragmentation of Alkyldisilane Ions in EIMS I. 1,1,2,2-Tetramethyldisilane.

The fragmentation of 1,1,2,2-tetramethyldisilane by using a deuterium labeling technique, a B/E linked scanning technique and ab initio MO methods was studied. In 70eV-EIMS the base peak was observed at m/z 59, which is produced by the simple cleavage of an Si-Si bond. It was confirmed by the ab initio MO calculation that the formation of this ion might occur predominantly. It was concluded that the abundant ion at m/z 73 was produced by a 1,2-hydrogen shift from one silicon atom to the other with simultaneous reverse shift of a methyl group.

Observation of positive and negative cluster ions in the fast atom bombardment mass spectra of tetraalkylammonium halopentacarbonylchromate salts

The positive and negative ion fast atom bombardment mass spectra of a series of individual and mixed tetraalkylammonium halopentacarbonylchromate salts have been recorded using mixed dimethylformamide + glycerol matrices. Selected ions have been subjected to collision induced dissociation using linked scanning techniques. Extensive cluster ion formation is observed and the data reveal that, although the chloride ion is most easily displaced from [CrX(CO) 5] −, iodide is least easy to displace from this ion. The fragmentation of bimetal anions by preferential loss of two CO ligands from one metal seems to indicate that this process is not accompanied by the formation of a metal—metal bond.

Formation and fragmentation of the [M + Na]+ ion of glycosides in fast atom bombardment mass spectrometry

AbstractPositive‐ion fast atom bombardment (FAB) mass spectra of flavonol and steroid glycosides with sodium chloride added showed well known characteristic features; of the appearance of [M + Na]+ peaks, disappearance of [M + H]+ peaks and a significant decrease in the peak heights of fragment ions. Compared with the features in the FAB mass spectra of crown ethers with addition of salt, and above features suggest a complexation between Na+ and the glycosides in matrix solution. The B/E‐constant linked scanning technique was used to obtain structural information of the [M + Na]+ ion of the glycosides. The B/E spectra gave the daughter‐ion peaks, suggesting that coordination of Na+ with the biosides and triosides occurs at the sugar moiety, whereas the coordination with the monoglycosides occurs at the aglycone moiety, except for monoglycosides in which the aglycone moiety does not contain significant oxygen functional groups such as OH and CO.

Primary structure determination of peptides and enzymically digested proteins using capillary liquid chromatography/mass spectrometry and rapid linked-scan techniques

Primary protein sequences were determined for both peptides and enzymatically digested proteins by rapid linked-scan (B/E) liquid chromatography/mass spectrometry/mass spectrometry (LC/MS/MS) at the low-picomole level (10-50 pmol). During the course of a single LC/MS/MS analysis, we demonstrated that it is possible to generate interpretable collision-induced dissociation spectra of the eluting proteolytic peptides. Molecular weights of tryptic peptides were established by using 1/10 of the protein digest by operating in the capillary LC/frit-FABMS mode. Peptides exhibiting the strongest MH+ ions were then selected for subsequent LC/MS/MS analysis (typically 1/5 of the remaining protein digest). Elution times for each chromatographic peak were generally greater than 30 s. It was therefore possible to obtain a minimum of six B/E fast linked-scan spectra during the course of elution of each peptide component. Typically, B/E linked scans of the greatest ion abundance (obtained at the chromatographic peak maximum) were averaged to enhance the signal/noise ratio at these low-picomole levels. Unit resolution was observed for product ions below m/z 1000. Rapid linked scanning by LC/frit-FABMS/MS provided mass assignments for product ions within 0.2-0.3 amu of theoretical values. Side-chain fragment ions (wn and dn) were also observed, which allowed for the differentiation of isobaric amino acids (e.g., leucine and isoleucine). Examples of the application of this fast linked-scan technique to LC/MS/MS are presented for complex mixtures of unknown peptides and the tryptic digestion of phosphorylated beta-casein.

Fragmentation pathways of O-trimethylsilyl ethers of dihydroxy long-chain bases analysed by linked-scan mass spectrometry

The fragmentation pathways of O-trimethylsilyl (TMS) ethers of long-chain bases were studied by the linked-scan technique and exact mass measurements of the characteristic ion of O-trimethylsilyl long-chain bases detected by gas chromatography combined with electron-impact mass spectrometry. The results indicate that there are three pathways: the M + − 15 (CH 3) − 90 (TMSOH) − 74 [OSi(CH 3) 2] series, the M + − 103 (CH 2OTMS) − 90 (TMSOH) series and the M + − 132 (CHNH 2CH 2OTMS) series.

Cluster ions in the secondary ion mass spectrometry of choline and acetylcholine halides

AbstractLiquid secondary ion mass spectra of choline and acetylcholine halides exhibit several series of cluster ions whose origins were investigated using B/E and B2/E linked‐scan techniques. In the case of choline halides three series of cluster ions were identified as (Me3\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm N}\limits^ + $\end{document}CH2CH2OH + nM), (Me3\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm N}\limits^ + $\end{document}CH2CH2OMe + nM) and (Me3N\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm N}\limits^ + $\end{document}CH2CH2OH · Me3\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm N}\limits^ + $\end{document}CH2CH2O− + nM), while (CH3COOCH2CH2\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm N}\limits^ + $\end{document}Me3 + nM), (Me3\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm N}\limits^ + $\end{document}CH2CH2OH + nM) and (CH2 = CH\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm N}\limits^ + $\end{document}Me3 + nM) were observed in the spectra of acetylcholine halides. For these cluster ions, bimolecular reactions induced on ion bombardment under secondary ion mass spectrometric conditions are discussed.

Analysis by fast atom bombardment mass spectrometry of 4,4-dicarboxy-5-(pyridoxyl-5'-phosphate)-proline, of 4-carboxy-5-(pyridoxyl-5'-phosphate)-proline and 4,4-dicarboxy-5-pyridoxylproline.

gamma-Carboxyglutamic acid (Gla) reacts easily and quantitatively with piridoxal-5'-phosphate in H2O at room temperature, to give the 4,4-dicarboxy-5-(pyridoxyl-5'-phosphate)-proline (1). This product has been characterized by fast atom bombardment (FAB) mass spectrometry, including the B/E linked scan technique, ultraviolet and 1H nuclear magnetic resonance (NMR) analysis. In order to support further on the structure of 1, the 4-monodecarboxyderivative (2), obtained by heating compound 1 at 100 degrees C for 30 min and the 5'-dephosphoderivative (3), obtained by enzymatic hydrolysis of 1 with alkaline phosphatase, were also analysed by FAB and 1H NMR techniques. FAB was shown to be the only adequate ionization technique to deal with such thermolabile and non-volatile compounds and could provide an elegant and fast method to detect Gla in biological matrices.

Characterization of acylcarnitines as their isobutyl ester derivatives using fast atom bombardment mass spectrometry and constant neutral loss scan

A simple method is described for the characterization of acylcarnitines by fast atom bombardment mass spectrometry in combination with constant neutral loss (CNL) scan. Acylcarnitines in urine are extracted using cation-exchange chromatography and derivatized to their isobutyl esters. The fragmentation patterns of these compounds are studied by various linked-scan methods including B/E, B2/E and B/E√(1 – E) scans. Acylcarnitine isobutyl esters are found to lose two specific neutral fragments simultaneously so that a CNL scan of the combined mass produces a much enhanced spectrum without most of the background peaks. An example is given in which the CNL scan is used to diagnose a patient with medium-chain acyl CoA dehydrogenase deficiency. The use of linked-scan techniques to monitor a specific metastable ion transition can be exploited for characterizing structurally related compounds and therefore the technique reported in this paper may have much wider applications to mixture analysis.

Structural analysis of choline phospholipids by fast atom bombardment mass spectrometry and tandem mass spectrometry.

The structures of intact choline phospholipids were determined by positive and negative ion mode fast atom bombardment mass spectrometry, tandem mass spectrometry, and B2/E and B/E constant linked scan mass spectrometry. The molecular weight of the choline lipid could be clearly determined by the appearance of [M + H]+ or [M + Na]+ in the positive ion mode and triplet ions, e.g., [M - 15]-, [M - 60]-, and [M - 86]-, in the negative ion mode. The structures of the triplet ions were assigned to [M - CH3]-, [M - HN(CH3)3]-, and [M - CH2 = CHN(CH3)3]-, respectively, by the MS/MS of each triplet ion, and the origin of the triplet ions was found as the matrix-ion adduct to the target molecule by using the B2/E linked scan technique. The polar group could be identified by the existence of ions indicating glycerophosphocholine and its cleavage products and by the presence of the triplet ions in the negative ion mode. Positional determination of the distribution of constituent fatty acyl groups was carried out by comparing the intensity of deacylated ions from positions 1 and 2 in the positive ion mode and of the ions produced by MS/MS of the triplet ions. From the mass number of the [RCOO]- ion which appeared in the negative ion mode, the molecular weight and degree of unsaturation of the fatty acyl group were determined. The position of double bond(s) in the acyl group was determined from the MS/MS of the [RCOO]- ion.