bluuebunny/crossref_metadata_2025_split huggingface dataset:
Utility of nicotinoyl derivatives in structural studies of mono‐ and diacylglycerols by gas chromatography/mass spectrometry. Part 1
Authors: Zöllner P. , Lorbeer E. , Remberg G. 
Published: May 2005

AbstractThe 1‐ and 2‐monoacylglycerols and 1,2‐ and 1,3‐diacylglycerols of saturated and unbranched fatty acids with 8, 10, 12, 14, 16 and 18 carbon atoms were synthesized and subsequently derivatized with nicotinic acid chloride hydrochloride. The resulting nicotinoyl derivatives were examined by mass spectrometry in the case of pure substances and as mixtures by gas chromatography/mass spectrometry (GC/MS). From the electron impact mass spectra, differentiation between mono‐ and diacylglycerols and between the two positional isomers of mono‐acylglycerols and diacylglycerols is possible. The molecular masses of the partial acylglycerols and the identities of the bonded fatty acid were also determined. Similarly to the nicotinoyl derivatives of saturated fatty alcohols, the nicotinoyl derivatives of partial acylglycerols produce a fragmentation pattern that reflects every methylene group of the alkyl chains. These results offer rules for the structure elucidation of partially acylated acylglycerols and probably for mixed diacylglycerols by means of GC/MS, which includes the detection of double bonds and methyl branch positions at the fatty acid alkyl chains. The molecular formulae of all the important fragments in the mass spectra of the nicotinoyl derivatives were confirmed by high‐resolution mass spectrometry. Their structures and fragmentation pathways are proposed.
Structural and substituent effects on [M]+.vs. [MH]+ formation in fast atom bombardment mass spectra of simple organic compounds
Authors: Nakata Hisao , Tanaka Katsunori 
Published: May 2005

AbstractThe peak intensity ratios of [M]+. vs. [MH]+ were measured in the fast atom bombardment (FAB) mass spectra of readily available test compounds with 3‐nitrobenzyl alcohol as the matrix. For simple aromatic amines, the ratio increases as the ionization energy of the substrate decreases. 4‐Substituted benzophenones showed preferential formation of [MH]+ ions, regardless of the nature of the substituents. This is probably due to the fact that the benzophenoes have carbonyl groups which can form hydrogen bonds with the matrix molecule. The peak intensity ratio is roughly proportional to the Hammett σ+. Among 4‐substituted biphenyls, both bromo and chloro substituents afforded abnormally high peak intensity ratios. The effects of the substituents in these compounds are discussed semi‐quantitatively in terms of the Hammett correlation and the hard and soft acids and bases principle. The mechanism of ion formation in FAB and chemical ionization (CI) ion sources appeared to be different because some of the compounds studied showed an intense [M]+. peak with a relatively weak [MH]+ peak in FAB spectra but exhibited a strong [MH]+ peak in ordinary CI spectra.
Chemical ionization mass spectra of simple 1,3‐dioxolanes and their sulphur analogues recorded with methane, isobutane, ammonia and acetone as reagent gas
Authors: Leinonen Aki , Vainiotalo Pirjo 
Published: May 2005

AbstractThe mass spectral behaviour of nine 1,3‐dioxolanes, seven 1,3‐dithiolanes and seven 1,3‐oxathiolanes was studied under chemical ionization conditions with ammonia, isobutane, methane, acetone, acetone‐d6 or pentan‐3‐one as reagent gas. The proton affinity of the first members in each series was not large enough for ammonia to protonate them; instead, the ionization took place through unstable [M + NH4]+ ions. Isobutane, which gave rise to abundant [M + H]+ ions in all cases, was the best reagent gas for the determination of the molecular mass. Methane chemical ionization caused extensive fragmentations either through ring cleavage or through the elimination of the largest substituent from ring positions 2 as a neutral hydrocarbon. The ketones used as reagent gas reacted to form adduct ions. In the case of dioxolanes and oxathiolanes, the [M + RCO]+ adduct ion decomposed through ring opening and then, as a consequence of intramolecular nucleophilic substitution, through the elimination of a neutral carbonyl compound. Resonance‐stabilized dioxolanylium and oxathiolanylium ions were obtained for dioxolanes and oxathiolanes, respectively. This reaction was almost non‐existent for the dithiolanes.
A linear free‐energy correlation in the low‐energy tandem mass spectra of protonated tripeptides Gly–Gly–Xxx
Authors: Morgan Daniel G. , Bursey Maurice M. 
Published: May 2005

AbstractThe backbone cleavages of protonated tripeptide ions of the series Gly—Gly—Xxx, where Xxx  Gly, Ala, Val, d‐Leu, l‐Leu, Ile, Phe, Tyr, Trp, Pro, Met and Glu, were studied in a hybrid tandem mass spectrometer. C‐Terminal y‐type ions and N‐terminal a‐ and b‐type ions were noted. A linear relationship between log (y1/b2) and the proton affinity of the C‐terminal amino acid substituents was found: as the proton affinity of the C‐terminal residue increases, the fraction of y1 ion formation increases. When the C‐terminal substituent was more basic than Trp, the b2 ion was not observed. It is likely that the site of protonation changes from peptide bond to side‐chain for just these residues, Lys, His and Arg.
From green algae to calcium inside buckyballs
Authors: Rose Harry R. , Dance Ian G. , Fisher Keith J. , Smith Derek R. , Willett Gary D. , Wilson Michael A. 
Published: May 2005

AbstractCoorongite and carbonaceous residues from coorongite pyrolysis at 450 and 500°C were studied by laser ablation Fourier transform mass spectrometry. Raw coorongite gave positive‐ion spectra having mainly protonated species of m/z 80–300 when laser ablated with a high laser power density. Endohedral fullerene positive ions of calcium were observed during the laser ablation of coorongite pyrolysis residues. Pyrolysis of the raw coorongite at 450 and 500°C produced residues which on laser ablation using the fundamental frequency of an Nd: YAG laser (1064 nm) gave a series of calcium fullerides. These ions were observed using low laser power densities (100–600 kW cm–2) Mixing the coorongite pyrolysis residue with barium sulphate gave M@Cn+ ionsThe symbol ‘@’, as in Ca@60, is used to represent an endohedral complex, i.e. the adduct is located inside the carbon cage.
where M = calcium or barium. Mixing the coorongite pyrolysis residue with strontium oxalate also gave M@Cn+ ions where M = calcium or strontium. No ions containing two or more metals were detected.
Gas‐phase fragmentation reactions of protonated glycerol and its oligomers: Metastable and collision‐induced dissociation reactions, associated deuterium isotope effects and the structure of [C3H5O]+, [C2H5O]+, [C2H4O]+. and [C2H3O]+ ions
Authors: Dass Chhabil 
Published: May 2005

AbstractThe chemistry of glycerol subjected to a high‐energy particle beam was explored by studying the mass spectral fragmentation characteristics of gas‐phase protonated glycerol and its oligomers by using tandem mass spectrometry. Both unimolecular metastable and collision‐induced dissociation reactions were studied. Collision activation of protonated glycerol results in elimiation of H2O and CH3OH molecules. The resulting ions undergo further fragmentations. The origin of several fragment ions was established by obtaining their product and precursor ion spectra. Corresponding data for the deuterated analogs support those results. The structures of the fragment ions of compositions [C3H5O]+, [C2H5O]+, [C2H4O]+. and [C2H3O]+ derived from protonated glycerol were also identified. Proton‐bound glycerol oligomers fragment principally via loss of neutral glycerol molecules. Dissociation of mixed clusters of glycerol and deuterated glycerol displays normal secondary isotope effects.
Novel use of an isotope separator to determine the position of fluorine‐18 in labelled 1,1,1,2‐tetrafluoroethanes
Authors: Pike Victor W. , Waters Stephen L. , Aigbirhio Franklin I. , Makepeace John , Tanner Richard J. N. 
Published: May 2005

AbstractA novel technique is described for measuring the site selectivity of methods for labelling the major CFC‐alternative, 1,1,1,2‐tetrafluoroethane (HFA 134a), with fluorine‐18 (t1/2 = 109.7 min). The carbon–carbon bond in radiofluorinated HFA 134a is broken in the ion source of an isotope separator. Radioactivity associated with the ion beam of the [CF2 18F]+. fragment (m/z = 68) is collected, measured and divided by the integrated mass of the simultaneously collected ion beam for the [CF3]+. fragment (m/z = 69) to give the ‘specific radioactivity’ (in nCi nmol–1) of the radiolabel in the 1‐position. Similarly, the ‘specific radioactivity’ of the radiolabel in the 2‐position is calculated from the measured radioactivity of the ion beam from the [CH2 18F]+. fragment (m/z = 32) and the integrated mass of the simultaneously collected ion beam from the [CH2F]+. fragment (m/z = 33). The selectivity of the labelling procedure for a particular position is then given by the decay‐corrected ratio of specific radioactivity at that position to the sum of specific radioactivities. The labelling of HFA 134a by the reaction of [18F] fluoride with trifluoroethylene was found to have 97% selectivity for the CF3 group, whereas labelling by the reaction of [18F] fluoride with 2,2,2‐trifluoroethyl p‐toluenesulphonate was found to have 91% selectivity for the CH2F group. This information is of value for tracer studies of the fate of HFA 134a in man following its inhalation as a drug propellant. The described technique is of potentially wider value for determining the position of fluorine‐18 in labelled polyfluorinated molecules.
Fast atom bombardment mass spectrometry of new polydentate schiff bases. 2. The case of mono‐ and bisaldimines containing pyridine groups
Authors: Coppola M. , Catinella S. , Traldi P. , Guerriero P. , Tamburini S. , Vigato P. A. 
Published: May 2005

AbstractThe mass spectrometric behaviour of seven polydentate Schiff bases derived from the condensation of formyl or diformyl precursors (2,3‐dihydroxy‐ or 2,5‐dihydroxy‐benzaldehyde, 3‐metoxy‐ or 3‐ethoxy‐salicylaldehyde, 3‐formyl‐salicyclic acid, 4‐methoxy‐ or 4‐chloro‐2,6‐diformylphenol) with 2‐aminomethylpyridine have been investigated by fast atom bombardment mass spectrometry and metastable ion studies.
Heats of formation of multi‐substituted positive ions of organic species
Authors: Luo Yu‐Ran , An Yan , Holmes John L. 
Published: May 2005

AbstractThe difference (ΔΔfH°) between heats of formation of many multi‐substituted odd‐ and even‐electron positive ions can be described by a linear equation: ΔΔfH° = A + Bm, where m is the number of substituents or ligands, relative to the unsubstituted reference ion, and m = 1, 2 or 3; A and B are the intercept and slope, respectively. The correlation quality for 59 types of odd‐ and 26 types of even‐electron ions, which involve C, Si, Sn, H, F, Cl, Br, I, O, S, N and P atoms, was analyzed. Unknown heats of formation of related ions and the proton affinities of some organic molecules were predicted using the linear equation.
Formation of M+. ions under matrix fast atom bombardment conditions: Does charge exchange reaction occur?
Authors: Takayama Mitsuo , Iwamura Michiko , Fuchibe Shohaku 
Published: May 2005

AbstractThe formation of molecular ions, M+., under fast atom bombardment (FAB) conditions using a liquid matrix was examined by using a new type of synthesized compounds in which preferential M+. peaks appear in their FAB spectra. The FAB spectra were compared with the corresponding mass spectra obtained by the electron impact (EI) ionization, chemical ionization (CI) and charge‐exchange ionization (CEI) methods. All of the spectra showed preferential peaks of M+. ion and a characteristic intense fragment ion peak originating from a β‐fission. The FAB spectra were similar in the fragment ions appearing in the EI spectra and were very similar in the fragmentation pattern to the CEI spectra using Ar+. and Xe+. as the reagent ions. Further, the FAB spectra did not show any doubly charged ion peaks, while the 70 eV EI spectra showed the peaks of doubly charged molecular and/or fragment ions. The isobutane CI spectra of the synthesized compounds suggested that the formation of M+. ions occurred through the CE reaction with isobutane ion, C4H10+., and the CI spectra showed a marked intense fragment ion peak originating from the β‐fission which seemed to occur characteristically in CEI processes. The results obtained suggested that the formation of M+. ions under matrix FAB conditions occurred mainly by CE reactions between the analytes M and matrix molecular ions B+. and/or fragment ions b+..
Mass spectrometric behaviour of simple oxazolidines under electron impact and chemical ionization
Authors: Lehtelä Pirjo‐Liisa , Smolander Risto , Vainiotalo Pirjo 
Published: May 2005

AbstractThe 70 eV electron impact mass spectra of 33 differently substituted oxazolidines were studied to determine the effect of substituents and the existence of the ring—chain tautomeric equilibrium on the decomposition of the molecular ions. Most of the fragmentations can be rationalized to start as the cleavage initiated by the radical site at nitrogen. Isomeric compounds showed different spectra and were easily differentiated. The position of the ring—chain equilibrium could be located only roughly. The chemical ionization mass spectra of the compounds were also recorded, with ammonia, isobutane, acetone or methane as reagent gas. Methane was the only reagent gas that promoted extensive fragmentation of the protonated molecules. However, no information about the position of ring‐chain tautomerism was obtained under these conditions. Analogously to other related five‐membered heterocycles, the oxazolidines reacted under acetone chemical ionization conditions to afford [M + CH3CO]+ adduct ions. These adducts were stable, however, and unlike those of 1,3‐dioxolanes and 1,3‐oxathiolanes, they did not decompose and form stable oxonium ions.
Multiphoton ionization and photodissociation at the second‐order space focus in a time‐of‐flight mass spectrometer: The amino acid tryptophan
Authors: Dey Michael , Grotemeyer Jürgen 
Published: May 2005

AbstractNeutral IR‐desorbed molecules of the amino acid tryptophan entrained in a supersonic beam were post‐ionized by multiphoton ionization (MUPI) in the gas phase. Variations in the intensity of the ionization laser produced different degrees of fragmentation observed in the time‐of‐flight mass spectra of tryptophan according to the ladder‐switching model for MUPI fragmentation. From the number of absorbed photons the upper values for the appearance energies of specific fragment ions were obtained. A complete fragmentation pathway of tryptophan was established by using photodissociation of molecular ions and fragment ions formed by MUPI. Photodissociation was successfully performed by secondary excitation with a UV laser at the second‐order space focus of a reflection time‐of‐flight instrument. A fragmentation tree for a laser‐desorbed molecule obtained in a laser tandem time‐of‐flight instrument is shown for the first time.
Tandem mass spectrometric analysis of fixed‐charge derivatized oligosaccharides
Authors: Domon B. , Mueller D. R. , Richter W. J. 
Published: May 2005

AbstractVarious derivatives of a set of three isomeric (linear and branched) pentasaccharides (LNF‐1, LNF‐2 and LNF‐3) were prepared and investigated by high‐performance tandem mass spectrometry in order to compare their collision‐induced dissociation (CID) behaviour. The fast atom bombardment tandem mass spectra of [M + H]+ ions of peracetylated derivatives mainly display fragments containing the non‐reducing terminus (B‐type ions) and allow a straightforward assignment of sugar sequence and branching together with the identification of some interglycosidic linkages. Permethylated derivatives, which better accommodate the mass range of tandem mass spectrometers in the case of larger oligosaccharides, yield similar results, i.e. predominance of B ions, but the necessary information has to be retrieved from incomplete Bi and Yi ion series. By contrast, CID of permethyl or peracetyl derivatives carrying a preformed charge due to prior reductive amination of the oligosaccharides with trimethyl(p‐aminophenyl)ammonium chloride yields exclusively fragment ions comprising the reducing end. In this case, the four distinct series of fragments observed involve charge‐remote fragmentation processes. As a consequence, the spectral patterns are not significantly affected by the nature of the sugar O‐substituents additionally introduced (i.e. methyl or acetyl).
Liquid secondary ionization, tandem and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometric characterization of glycosphingolipid derivatives
Authors: Perreault Hélène , Costello Catherine E. 
Published: May 2005

AbstractPermethylated, peracetylated and perbenzoylated derivatives of glycosphingolipids (GSLs) were prepared to compare their liquid secondary ionization mass spectrometric (LSIMS) and collision‐induced dissociation tandem mass spectrometric (CID/MS/MS) fragmentation patterns and also to determine sensitivity improvement in LSIMS and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOFMS) relative to the native species. Permethylation was carried out in the liquid phase, whereas peracetylation and perbenzoylation could be effected using either liquid (bulk)‐phase or gas‐phase procedures. Lower amounts of starting material were required for the gas‐phase derivatization (⩽ 100 pmol) compared with the bulk phase (⩽1 nmol), because the former method permits more efficient sample handling. All three types of derivatives yielded sensitivity improvements of at least two orders of magnitude over the native species in both LSIMS and MALDI‐TOFMS. The behavior of the permethylated compounds was used as the benchmark for GSL structural information content in normal and tandem mass spectra. Fragments present in spectra of the three types of derivatives generated complementary information. Permethylated GSLs favored the formation of ions related to the ceramide moieties, whereas peracetylation enhanced the production of carbohydrate‐related ions. The LSI mass spectra of perbenzoylated GSLs contained information on both ceramide and sugar portions of the molecules. Each of the LSIMS, MS/MS and MALDI‐TOFMS techniques proved to be complementary to the others in this study; the use of all three is recommended for the generation of complete structural information.
Profiling glycosphingolipid structural detail: Periodate oxidation, electrospray, collision‐induced dissociation and tandem mass spectrometry
Authors: Reinhold Bruce B. , Chan Shui‐Yung , Chan Steven , Reinhold Vernon N. 
Published: May 2005

AbstractElectrospray ionization mass spectrometry applied to methylated glycosphingolipid samples provides a sensitive molecular mass profile with no detectable fragmentation and little matrix background. In a bovine brain preparation, the components GM1a, GD1a/b and GT1a/b were characterized in detail and several minor entities, GT1, GM3, GA1, GM2, were mass profiled. Two additional materials, unrelated to the o‐, a‐, b‐ or c‐series, were characterized as hexosamine additions to GM1 and GD1a. Structural details of the major components within these samples were obtained by utilizing low‐energy collision tandem mass spectrometry and periodate oxidation, which could serve as a basis for more complex and higher molecular mass preparations. Fragment structures in the collision spectra were assigned with the assistance of C1H3 and C2H3 derivatization and by exploiting the natural carbohydrate and ceramide heterogeneity of the samples. Major fragments originate from C1O glycosidic rupture with few ring‐opening ions. Glycosidic fragments defined details that allow the determination of structural isomers, while specific fragments of the ceramide moiety differentiate sphingosine from N‐acyl heterogeneity. When contrasted with high‐energy (8 keV) tandem mass spectrometry, low‐energy collision‐induced dissociation of multiply charged molecular ions provided more abundant structurally diagnostic fragments.
Examination of complex oligosaccharides by matrix‐assisted laser desorption/ionization mass spectrometry on time‐of‐flight and magnetic sector instruments
Authors: Harvey D. J. , Rudd P. M. , Bateman R. H. , Bordoli R. S. , Howes K. , Hoyes J. B. , Vickers R. G. 
Published: May 2005

AbstractMatrix‐assisted laser desorption/ionization (MALDI) spectra of underivatized oligosaccharides of the type attached to asparagine in glycoproteins (N‐linked oligosaccharides) were examined with linear time‐of‐flight (TOF) and magnetic sector instruments using 2,5‐dihydroxybenzoic acid (2,5‐DHB), α‐cyano‐4‐hydroxycinnamic acid, sinapinic acid, 1,4‐dihydroxynaphthalene‐2‐carboxylic acid or 2‐(4‐hydroxyphenylazo)benzoic acid (HABA) as the matrices. All compounds formed abundant [M + Na]+ ions with the strongest signals being obtained from 2,5‐DHB after recrystallization of the initially dried sample spot from ethanol. Only traces of fragmentation were detected from neutral oligosaccharides on the TOF system but more abundant fragment ions (about 5% relative abundance) were present in the spectra from the magnetic sector instrument. Fragmentation was dominated by Y‐type glycosidic cleavages (Domon and Costello nomenclature) between all sugar residues yielding sequence and branching information. Sialic acid‐containing oligosaccharides generally produced the sodium adduct of the sodium salt and gave much weaker signals than the neutral sugars in the positive‐ion mode. There was also considerable loss of the sialic acid moleties as the result of fragmentation on the magnetic sector instrument. The least fragmentation of both neutral and acidic sugars was caused by 2.5 DHB, which proved to be the most appropriate matrix for examination of oligosaccharide mixtures. Much better resolution of the oligosaccharides was obtained than by traditional methods such as the use of Bio‐Gel P‐4 gel filtration column chromatography. It is worth noting also that the measurements were considerably faster (a few minutes as opposed to about 16 h). In addition, no radiolabelling was necessary as required for detection on the P‐4 columns. Mixtures of oligosaccharides from several glycoproteins (ribonuclease B, human immunoglobulin G (IgG) transferrin, bovine fetuin and chicken ovalbumin) were examined and the patterns of the identified oligosaccharides were found to agree closely with the known compositions of the sugar mixtures. The mass spectrometric resolution on the magnetic sector instrument was very much better (up to 3000, FWHM) than could be obtained with the linear TOF systems (200–400). The technique was used as a detection system for the products of exoglycosidase digestion in experiments to determine the detailed structure of the oligosaccharide chains from human IgG.