Fast Atom Bombardment Spectra Research Articles

Thioglycerol matrix interactions in the positive ion fast atom bombardment mass spectrometry of several Hantzsch and Biginelli ester derivatives of boronic acids

Fast atom bombardment (FAB) ionization is a valuable tool for analyzing non-volatile or thermally labile compounds when harder ionization methods (EI or CI) have been unsuccessful. Unexpected interactions between matrix and analyte may, however, occur in FAB ionization leading to the formation of artifacts whose structures have to be determined. We used esters synthesized by our research group following green chemistry protocols. Artifacts relating to the target molecules were produced in the solvent cage using positive ion FAB using thioglycerol as the matrix and analyzed by accurate mass measurement. Through interactions between thioglycerol and the boron atom, various adducts associated with boron-containing Hantzsch and Biginelli ester derivatives appeared in the FAB mass spectra. These interactions must arise in a solvent cage involving a Lewis acid-base bond. Accurate mass determinations of these adducts confirmed the presence of the target molecules. Interactions between the thioglycerol matrix and the eleven boron-containing Hantzsch and Biginelli ester derivatives in addition to the three reagents were seen in their FAB(+) spectra. These interactions, together with their accurate mass determinations, allowed us to determine the structures of the new molecules.

Mass Spectra Analyses of Amides and Amide Dimers of Steviol, Isosteviol, and Steviolbioside

The mass spectra of a series of stevioside analogues including the amide and dimer compounds of steviol, isosteviol, and steviolbioside were examined. Positive ion mass spectral fragmentation of new steviol, isosteviol, and steviolbioside amides and the amide dimers are reported and discussed. The techniques included their synthesis procedures, fast-atom bombardment (FAB), and LC/MS/MS mass spectra. Intense [M+H]+ and [M+Na]+ ion peaks were observed on the FAB and ESI spectra. LC/MS/MS also yielded ES+ and ES− ion peaks that fairly agreed with the results of the FAB and ESI studies. Mass spectral analysis of compounds 4p-q, 5a-g, 6, and 7 revealed the different cleavage pathway patterns that can help in identifying the structures of steviolbioside and its amide derivatives.

ChemInform Abstract: Mass Spectrometry of Prenylated Flavonoids

The fragmentation patterns originating from the degradation of prenyl group(s) in positive ion electron ionization (EI), fast-atom bombardment (FAB) and chemical ionization (CI) mass spectrometry (MS) of prenylated flavonoids were reviewed. The EI spectra showed the characteristic fragmentation patterns reflecting the location of prenyl group in the flavonoid compounds, whereas the FAB and CI spectra showed relatively monotonous patterns. It was described how the EI and FAB fragmentation patterns are useful for the identification of prenylated flavonoids

Determining the structure of glycan moieties by mass spectrometry.

Acquisition of mass spectra using fast-atom bombardment (FAB), matrix-assisted laser desorption/ionization (MALDI), and electrospray ionization (ESI) mass spectrometry is summarized in this unit. Molecular weights of the carbohydrates provide information on their composition in terms of isobaric monosaccharide composition, and tables of residue masses are provided to assist these calculations. More detailed structural analysis can be performed by fragmentation; the main fragmentation modes of carbohydrates and their nomenclature are discussed. Fragmentation of negative ions generated by nano-electrospray, in particular, provide very informative spectra and give details such as the position of fucose substitution, branching pattern, and the presence or absence of bisecting GlcNAc residues. Practical details are given for the purification of samples prior to mass spectrometric analysis and for recording FAB, MALDI, and ESI spectra.

Mass spectral studies on aryl‐substituted N‐carbamoyl/N‐thiocarbamoyl narcotine and related compounds

Positive ion mass spectral fragmentation of new N-carbamoyl/N-thiocarbamoyl derivatives of narcotine and compounds closely related to it are reported and discussed. The techniques used include electron impact (EI), fast-atom bombardment (FAB), matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) and electrospray ionization tandem mass spectrometry (ESI-MS/MS). Prominent peaks in the mass spectra of these compounds appear to involve C-C bond cleavage beta to the amine nitrogen with loss of the 4,5-dimethoxy(1H)isobenzofuranone moiety from their molecular ions, along with another prominent peak at m/z 382. No molecular ion peaks of these compounds were recorded in EI, whereas intense [M + H]+ ion peaks were observed in FAB and ESI spectra. MALDI also yielded [M + H]+ ion peaks in good agreement with FAB and ESI studies.

Studies of Unsaturated C-Aryl Glycosides by Fast-Atom Bombardment Mass Spectrometry

Fast-atom bombardment (FAB) spectra, FAB mass-analyzed ion kinetic energy (FAB MIKE) spectra and FAB MIKE spectra with collision-activated dissociation (FAB CAD-MIKE) were obtained for some unsaturated anomeric C-aryl glycosides. Although the FAB MIKE and FAB CAD-MIKE spectra of the [M + H]+ ion showed no differences, differentiation of the regioisomers and anomers was possible by analyzing the MIKE and CAD-MIKE spectra of the [M + Li]+ or [M + Na]+ ions.

Mechanism of cross-ring cleavage reactions in dirhamnosyl lipids: effect of the alkali ion.

Liquid secondary ion mass spectrometry and high-energy collision-induced dissociation were used to analyze a dirhamnosyl lipid mixture. The negative fast-atom bombardment spectrum reveals a mixture of four homologous dirhamnosyl lipids with the following general structure: Rha-Rha-Cn-Cm (where Cn and Cm denote 3-hydroxy fatty acid moieties). The mass region 450-600 u in the collision-induced dissociation spectra of the negative [M - H]- ions shows product ions that can be rationalized by terminal loss of a 3-hydroxyalkanoic acid residue; these ions can be used for the characterization of the fatty acid substituents. A unique effect of alkali-metal ions on the course of fragmentation of dirhamnosyl lipid attachment ions was observed. The strong chelation of sodium is revealed from the stability of the [M - H + 2Na]+ ion that does not lose a sodium ion with the eliminated neutrals, contrary to what is observed for the dilithium adduct. Cross-ring cleavages occur during high-energy collision-induced dissociation of both positively and negatively charged precursor ions. The results suggest a concerted decomposition pathway involving the six-membered rings of the monosaccharide residues. The formation of cross-ring cleavage products, which retain the C10-C10 moiety during high-energy collision-induced dissociation of all the precursor ions that contain sodium or lithium, strongly supports a retro [2 + 2 + 2] mechanism.

Negative fast atom bombardment ionization of aromatic sulfonic acids: unusual sample-matrix interaction.

The most intense ion(s) in negative ion fast atom bombardment (FAB) mass spectra of 2- and 4-benzaldehyde sulfonic acid (BSA) in glycerol or 3-nitrobenzyl alcohol matrix corresponds to a covalent association of the analyte with one or two matrix molecules accompanied by the elimination of a molecule of water. The molecular ion [M - H](-), however, is of low abundance. The identity of the resulting ions [M + nA - H(2)O - H](-) (where M is the analyte and A is the matrix) was confirmed by exact mass measurement using the peak matching technique. These covalent matrix-analyte complexes were not observed when the sulfonic acid functionality in BSA was substituted with COOH, NO(2), and OH or when the sulfonic acid was in salt form. These observations indicate that the free sulfonic acid group in BSA is responsible for the covalent adduct formation. To our knowledge, analyte-matrix covalent association in negative ion FAB spectra of BSA has not been reported previously.

Structural study of PLGA [copoly (DL-lactic/glycolic acid)], a biodegradable polymer for parenteral sustained release preparations, by tandem mass spectrometry.

A copoly (DL-lactic/glycolic acid) (PLGA), with a weight-average molecular weight of about 8400, has been characterized using fast atom bombardment (FAB)-tandem mass spectrometry in order to determine the sequence. Because of the large molecular size, PLGA was partially hydrolyzed and the terminal hydroxyl groups in the resulting oligomer mixture acetylated as the indicator. The FAB spectrum of this sample showed a complex ion signal pattern containing monomer to octamer. Diagnostic product ions containing useful information for sequence determination were observed in collision-induced dissociation-MS/MS and MS/MS/MS of these oligomer ions. The results of analysis for dimers through pentamers showed that they have random sequences of lactic and glycolic acid, suggesting that the whole structure of PLGA also has a random sequence.

Characterization of carbohydrates using a combination of derivatization, high-performance liquid chromatography and mass spectrometry

A combination of derivatization methods, chromatographic techniques and mass spectrometric ionization modes have been explored for the characterization of small sugars and medium-size oligosaccharides. Derivatization using 1-phenyl-3-methyl-5-pyrazolone (PMP) was preferred over pyridylamination (PA) owing to the simplicity of the reaction method, and also to enhanced ionization efficiency of the PMP derivatives relative to aminopyridyl sugars. The good quality and ease of separation of PMP derivatives by high-performance liquid chromatography were also advantages of using PMP derivatization rather than pyridylamination. PMP- and PA-monosaccharides produced abundant ions by either fast atom bombardment (FAB), electrospray ionization (ESI) or matrix-assisted laser desorption/ionization (MALDI). The PA and PMP derivatives of lactose, fucosyllactose and sialyllactose yielded FAB spectra with low S/ N ratios, whereas ESI and MALDI produced better spectra with a hundredth of the material used for FAB. In general, PMP derivatives of these di- and trisaccharides gave rise to stronger signals than PA analogs. For oligosaccharides containing more than three sugar rings, only PMP was used for derivatization, FAB was dropped and only ESI and MALDI were utilized.

High levels of (24S)-24-hydroxycholesterol 3-sulfate, 24-glucuronide in the serum and urine of children with severe cholestatic liver disease

Extracts of urine and serum from children with cholestatic liver disease were analyzed by fast atom bombardment (FAB) mass spectrometry. About half of all spectra showed a peak at m/z 657, compatible with the presence of a glucuronidated cholestenediol sulfate. Separation by ion exchange chromatography before and after solvolysis and treatment with beta-glucuronidase, combined with analyses by gas chromatography-mass spectrometry and FAB mass spectrometry with collision-induced dissociation, showed that the major compound responsible for the peak at m/z 657 was (24S)-24-hydroxycholesterol 3-sulfate, 24-glucuronide. The double conjugate of 27-hydroxycholesterol was also identified and double conjugates of cholestene- and cholestanetriols were also present. Semiquantitative analyses of the double conjugate of 24-hydroxycholesterol in patients whose FAB spectra showed a peak at m/z 657 indicated serum levels of 2-18 microM and a daily urinary excretion of 0.1-2.7 mumol/24 h. Eleven of 13 studied patients with a prominent peak at m/z 657 in the FAB spectra of their serum or urine either underwent liver transplantation or died. It is concluded that double conjugation of hydroxysterols with sulfuric and glucuronic acids can be an important metabolic pathway, particularly for (24S)-24-hydroxycholesterol. It is speculated that serious cholestatic liver disease may induce an increased formation and release of (24S)-24-hydroxycholesterol from brain (Lütjohann et al. 1996, Proc. Nutl. Acad. Sci. USA. 93: 9799-9804) with subsequent extracerebral conjugation with sulfuric and glucuronic acids.

If the ionization mechanism in fast-atom bombardment involves ion/molecule reactions, what are the reagent ions? The time dependence of fast-atom bombardment mass spectra and parallels to chemical ionization

The evaporation in vacuo of the matrices used and the particle-induced desorption of matrix molecules in fast-atom bombardment (FAB) contribute to a proposed high pressure region above the FAB matrix known as the selvedge region. If the neutral number density is sufficiently high, ions formed upon bombardment may undergo collisions with molecules, yielding matrix-related cluster ions and, in cases when the analyte is desorbed in neutral form, protonated and deprotonated analyte molecules. Similarities with the chemical ionization (CI experiment have been pointed out previously and are further developed here. If FAB is similar to CI, then the response depends on the structures of the reagent ions — those ions that react with gas phase analyte molecules. We consider here the time dependence of positive and negative ion FAB spectra to attempt to identify the reagent ions of FAB. A model is suggested for the FAB ion source which evaluates similarities to a CI source, as well as spatial aspects that are unique to desorption/ionization techniques.

Mass spectrometric characterization of telechelic prepolymers and addition polymers of DGEBA-aliphatic amines

Plasma desorption (PD) mass spectra of high molecular weight addition polymers of 2.2-bis-[4-(2.3-epoxypropoxy)phenyl]propane (DGEBA) and benzylamine show protonated molecular ions of the intact polymers and oligomer molecules. In the spectrum of a DGEBA/N,N′-dibenzyl-5-oxanonanediamine-1.9 addition polymer only fragments of the oligomers and a cyclic oligomer are observed. In both polymer spectra there is no indication for side reactions during the addition polymerization such as ether formation. Fast-atom bombardment (FAB) spectra of telechelic prepolymers having amino end groups show the regular oligomers with increasing degree of polymerization and the expected fragmentation products. Only prepolymers with epoxide end groups contain the regular prepolymers as well as side reaction products which are formed by reactions of the telechelics and DGEBA or by reaction of themselves. © 1996 John Wiley & Sons, Inc.

Study of the Interaction of Dinucleotide Analogs with Alkaline Earth Metal Ions by Fast Atom Bombardment Mass Spectrometry

The fast atom bombardment (FAB)mass spectra of a series of dinucleotide analogs, compounds 1–8 with alkaline earth metal chlorides (CaCl2, MgCl2, SrCl2 and BaCl2) were studied in a thioglycerol matrix. The positive-ion FAB mass spectra of 1–8 with CaCl2 gave [M+Ca-H]+, [M+CaCl]+ and [M+Ca2Cl-2H]+ ions. The formulae of [M+Ca-H]+ and [M+Ca2Cl-2H]+ ions from 2 were confirmed with high-resolution measurements. Compounds 1–8 with alkaline earth metal ions also give metal chelated dimerized species [2M+Ca3Cl-4H]+, [2M+Ca2-3H]+ and [2M+Ca-H]+], a process which is independent of the size of the polyether chain. The negative-ion FAB spectra also produce bimetallic ions with all substrates studied. Experiments with D2O addition using CaCl2 with compounds 2 and 6 suggested the elimination of acidic protons (amide and/or amine) in the formation of [M+MetxCly-nH] ions in either positive or negative modes. The site of the metal chelation was the same in both positive-and negative-ion mass spectra. The collision-activated dissociation data suggest the covalent bonding of the metal to the nitrogen base and coordination with the polyether chain.

Reduction by Electron and Hydride Attachment to Doubly Charged Heterocyclic Cations in Fast-atom Bombardment Mass Spectrometry. Influence of the Matrix

A study of the fast-atom bombardment spectra of positive ions which result from doubly charged heterocyclic cationic compounds shows the influence of the matrix on the nature of the spectrum. While two reduction reactions are encountered with glycerol (electron and hydride anion attachment), the spectrum obtained with m-nitrobenzyl alcohol only contains three expected ions with significant abundance, viz. the doubly charged cation, the deprotonated cation and the adduct ion with a bromide anion.

Observation of alkali-metal-carboxylate radical anions in fast-atom bombardment

The existence of a series of 32 molecular radical anions from carboxylic acids salts RCOO-Cat(-), where R = CH3, CH3CH2, CH3CH2CH2, (CH3)2CH, C6H5, o-CH3-C6H4, m-CH3-C6H4, and p-CH3-C6H4 and Cat = Li, Na, K, Rb, has been proven by the observation of their fragmentation in negative-ion fast-atom bombardment tandem mass spectrometry. These species occur at very low abundance and are not detected in the fast-atom bombardment spectra because they are hidden in the background. However, the collision-induced dissociation fragmentation of ions selected at the mass-to-charge ratio values that correspond to these species display characteristic signals that are completely different from the signals observed from pure matrix or after addition of corresponding metal hydroxide to the matrix. The main fragmentation observed is the loss of the neutral metal atom from RCOOCat(-·), followed by a loss of CO2 for the aromatic compounds. Neutral loss experiments also confirm the existence of these radical anions. Scans for the loss of a selected metal after addition of one of the carboxylic acid salts to the matrix display abundant peaks at mass-to-charge ratio values that correspond to the salt radical anions. Some weaker peaks appear at other mass-to-charge ratio values independent of the salt that is used and also are observed from the matrix when the corresponding metal hydroxide is added. When alkali metal salts from some deuterated acids are analyzed, the predicted shifts are observed. The loss of the neutral metal is more pronounced from RCOONa(-·), RCOOK(-·), and RCOORb(-·) than from RCOOLi(-·).

Formation by fast atom bombardment of molecular radical cations by electron donor–acceptor complexes from tosylated amino acid esters

AbstractN‐Alkyl‐N‐tosyl amino acid esters were ionized by fast atom bombardment (FAB) in a nitrobenzyl alcohol matrix through oxidative processes leading to molecular radical cations (M+·). The addition to the matrix of Cu11 salts induces the ionization through proton attachment whereby [M + H]+ are exclusively displayed by the positive‐ion FAB spectra. The formation of electron donor–acceptor complexes between the analytes and the matrix lowers the critical energy for the ionization by one‐electron removal from the substrates.

Fast-atom bombardment mass spectrometry and low energy collision-induced tandem mass spectrometry of tauroconjugated bile acid anions

Fragmentation of negative ions produced by fast-atom bombardment (FAB) from 14 tauroconjugated bile acids and some of their deuterated analogs has been studied by mass spectrometry and by collision-induced dissociation (CED) tandem mass spectrometry at low energy.Low energy collision-induced dissociation of the deprotonated molecules [M - H](-) of these tauroconjugated bile acids leads to both charge-driven and charge-remote fragmentations (CRF). The former yields neutral loss from the side chain with charge migration during the fragmentation process. These fragments dominate the CID spectra, but are absent from the FAB spectra. Their relative abundances are dependent on the number and the positions of the hydroxyl groups in the steroid nucleus and thus permit distinction among some positional isomers.The CRF fragments correspond to cleavages in the side chain up to fragmentations across the steroid rings with charge retention on the sulfonate group. These CRF fragments, which also are useful for structural identification, are less intense in CID than in FAB spectra. It appears that these charge-remote fragments are favored by unsaturation in the steroid rings, either as keto groups or as endocyclic double bonds. Tandem mass spectrometry combined with the use of deuterated analogs demonstrates that the structures of the survivor pseudomolecular ions and of the CRF fragments are not rearranged.

An Unusual Polar Lipid from the Cell Membrane of Mycoplasma fermentans

The major unidentified polar lipid (compound X), recently demonstrated in the cell membrane of Mycoplasma fermentans, was purified by preparative silicic acid column chromatography. Chemical analyses of acid-hydrolyzed compound X revealed that, in addition to fatty acids, it contains glycerol, choline and phosphate in a molar ratio of approximately 1:1:2, and an amino acid that has a retention time similar to that of homoserine. The methylated fatty acid fraction of compound X was subjected to gas-liquid chromatography and revealed methyl palmitate and methyl stearate in a 4.6:1 molar ratio. The structure of compound X was further analyzed by combining mass spectrometry, 31P-NMR and 1H-NMR. The positive and negative fast atom bombardment spectra showed a major component of M(r) 1048 and a minor component of M(r) 1076. Two different phosphate groups were identified in each of the components by 31P-NMR. Fast atom bombardment, tandem mass spectrometry, negative and positive chemical ionization mass spectrometry together with mass spectra analyses of the water-soluble and ether-soluble products obtained by methanolysis has shown that, in addition to palmitic and stearic acid residues, the presence of glycerol, ribitol, cholinephosphate and homoserinephosphate residues. It is suggested that the apparent structure of compound X is either a phosphatidylcholine attached via a phosphotriester bond to a ribitolphosphohomoserine moiety or a phosphatidylhomoserine attached via a phosphotriester bond to a ribitolphosphocholine moiety. The major molecular species is the dipalmitoylderivative (M(r) 1048), whereas the minor molecular species is a stearoyl palmitoyl derivative (M(r) 1076).

An Unusual Polar Lipid from the Cell Membrane of Mycoplasma fermentans

The major unidentified polar lipid (compound X), recently demonstrated in the cell membrane of Mycoplasma fermentans, was purified by preparative silicic acid column chromatography. Chemical analyses of acid‐hydrolyzed compound X revealed that, in addition to fatty acids, it contains glycerol, choline and phosphate in a molar ratio of approximately 1:1:2, and an amino acid that has a retention time similar to that of homoserine. The methylated fatty acid fraction of compound X was subjected to gas‐liquid chromatography and revealed methyl palmitate and methyl stearate in a 4.6:1 molar ratio. The structure of compound X was further analyzed by combining mass spectrometry, 31P‐NMR and 1H‐NMR. The positive and negative fast atom bombardment spectra showed a major component of Mr 1048 and a minor component of Mr, 1076. Two different phosphate groups were identified in each of the components by 31P‐NMR. Fast atom bombardment, tandem mass spectrometry, negative and positive chemical ionization mass spectrometry together with mass spectra analyses of the water‐soluble and ether‐soluble products obtained by methanolysis has shown that, in addition to palmitic and stearic acid residues, the presence of glycerol, ribitol, cholinephosphate and homoserinephosphate residues. It is suggested that the apparent structure of compound X is either a phosphatidylcholine attached via a phosphotriester bond to a ribitolphosphohomoserine moiety or a phosphatidylhomoserine attached via a phosphotriester bond to a ribitolphosphocholine moiety. The major molecular species is the dipalmitoylderivative (Mr 1048), whereas the minor molecular species is a stearoyl palmitoyl derivative (Mr 1076).