Fast Atom Bombardment Spectrometry Research Articles

Synthesis, characterization and crystal structure of new copper(II) complexes with tris- and tetrakis-(pyrazol-1-yl)borate ligands

The synthesis and characterization of six new copper(II) complexes [H n B(pz) 4− n ] 2Cu (pzH=3-methyl- or 4-methyl-pyrazole, n=1 or 0; pzH=3,5-dimethyl-4-chloropyrazole or 3,4,5-trimethylpyrazole, n=1) are reported. X-ray crystal structure studies were performed for [HB(3-Mepz) 3] 2Cu, [HB(4-Mepz) 3] 2Cu, [HB(3,5-Me 2-4-Clpz) 3] 2Cu, and [B(3-Mepz) 4] 2Cu, all of which are in a strongly distorted octahedral environment. Some derivatives were also characterized with fast atom bombardment spectrometry and magnetic susceptibility measurements.

Electrogeneration of conducting poly(2,5-di-(-2-thienyl)-furan)

Abstract The electrochemical behaviour of 2,5-di-(-2-thienyl)-furan (SOS) on Pt has been studied in 0.2 M LiClO 4 +acetonitrile+0.25% (v/v) water solutions by cyclic voltammetry, chronoamperometry and chronopotentiometry. The monomer oxidises at more positive potentials than 0.7 V vs. Ag|AgCl giving a dark-blue film. The most reproducible film weights are obtained by flowing a constant current lower than 1.0 mA cm −2 . The resulting insoluble oxidised films are electroactive and electrochromic. Their control voltammograms exhibit two redox processes attributed to polaronic and bipolaronic states, together with an intermediate reduction shoulder ascribed to radical cation pairs. Electropolymerisation kinetics have been followed by `ex situ' ultramicrogravimetry, giving a maximum productivity of 1.85 mg mC −1 . The oxidised poly(SOS) contains polarons and electroinactive positive charges, both compensated with perchlorate counterions. The reduced poly(SOS) has been obtained in the same electrolyte by applying a constant potential of 0 V to oxidised films. A partial electrodissolution of films is observed during their reduction. The electroinactive charges present in the resulting reduced state cause its insolubility in the medium. Densities, conductivities and solubilities in different organic solvents of both oxidised and reduced poly(SOS) have been determined. Short linear oligomers formed during SOS electropolymerisation have been detected in the saturated solutions of reduced poly(SOS) by mass spectrometry-fast atom bombardment.

Structural elucidation of a novel lysine-lysine crosslink generated in a glycation reaction with L-threose

A novel lysine-lysine crosslink was isolated from a reaction containing L-threose (a degradation product of ascorbic acid) and N-α acetyllysine. The compound, after chromatographic purification, had a relative molecular mass of 628 as determined by fast atom bombardment spectrometry. Structural analysis by NMR spectroscopy (1H,13C, COSY, HETCOR and DEPT) suggests that the compound is composed of 3 threose residues and 2 N-α-acetyllysines with an empirical formula of C28H45N4O12. The compound, referred to as threosidine (2,5-dihydroxy-5,6,7,8-tetrahydro 1,7-naphthyridinium as the core molecule) has an absorption maximum at 328 nm with an excitation and emission maxima at 328 nm and 402 nm respectively. Threosidine was stable upon acid hydrolysis, and it was not found in the reactions containing threose and amino acids other than N-α-acetyllysine. Threosidine was also not found in the reactions containing N-α-acetyllysine and sugars other than threose.

Xanthurenic acid derivative formation in the lens is responsible for senile cataract in humans.

The tryptophan degradation pathway leads to NAD production via 3-hydroxykynurenine. Kynurenine aminotransferase (KAT) transforms 3-hydroxykynurenine into xanthurenic acid. In this study, we measured the activity of KAT in human lenses and studied the consequences of xanthurenic acid formation KAT activity was determined by the method of Tobes. Fluorescence spectroscopy and SDS-PAGE were used for the protein studies. Thin-layer chromatography and infrared and fast atom bombardment spectrometry were used for substance characterization. The KAT activity was detected in senile cataratous lenses, but was absent in the young lenses. Xanthurenic acid at physiological pH exists in equilibrium with its tautomeric form reported by us as oxo-xanthurenic acid (OXA), which is oxidized to di-oxoxanthurenic acid (DOXA), a naphthoquinone-like substance. The incubation of DOXA with crystallins in a solution of physiological pH led to crystallin crosslinking and formation of conjugates with glutathione. Xanthurenic acid is formed in human lenses. Its tautomerization and oxidation leads to a naphthoquinone-like substance, DOXA. DOXA provoked formation of conjugates with glutathione and crosslinking of crystallins. Thus, KAT activity seems to be the initial event in senile cataract formation in humans.

HPLC Separation of Cephalotaxine, Harringtonine and Homoharringtonine from Callus and Root Cultures ofCephalotaxus Harringtonia

Abstract A simple extraction and analytical protocol was developed to assay cephalotaxine, harringtonine, and homoharringtonine from callus and root cultures of Cephalotaxus harringtonia. The process involves extraction by methanol followed by partitioning between 0.5% ammonium hydroxide and chloroform. The chloroform fraction recovered greater than 90% of all three alkaloids. This fraction was concentrated to dryness, resuspended in methanol and analyzed by high pressure liquid chromatography using a UV detector. Peaks corresponding to all three alkaloids were identified by comparing their retention times with authentic standards and their identity confirmed by fast atom bombardment spectrometry. The root cultures contained higher levels of harringtonine and homoharringtonine (2.4 and 3.9 mg/kg dry matter, respectively) compared to the callus cultures; however, the levels of cephalotaxine were comparable (10.2 mg/kg dry matter).

Separation and characterization of five positional isomers of trimaltosyl-cyclomaltoheptaose (trimaltosyl-β-cyclodextrin)

Trace amounts of trimaltosyl-cyclomaltoheptaoses (trimaltosyl-β-cyclodextrins, trimaltosyl-βCDs) were found in a mixture of maltosyl-cyclomaltoheptaoses (maltosyl-β-cyclodextrins, maltosyl-βCDs) prepared from maltose and cyclomaltoheptaose (β-cyclodextrin, βCD) through the reverse action of Klebsiella pneumoniae pullulanase. Five positional isomers of trimaltosyl-βCD were isolated by high-performance liquid chromatography (HPLC) on a reversed-phase column and a graphitized carbon column. For the structural analysis of 6 1, 6 2, 6 3-, 6 1, 6 2, 6 5-, and 6 1, 6 3, 6 5-tri- O-maltosyl-βCDs, an enzymic method using glucoamylolysis, followed by hydrolysis with Bacillus subtilis saccharifying α-amylase, was applied. Although 6 1, 6 2, 6 4- and 6 1, 6 2, 6 6-substituted isomers were indistinguishable by this method, these isomers were distinguished clearly by digestion of branched oligosaccharides produced from each isomer by the aofresaid method, with B. stearothermophilus neopullulanase or with glucoamylase. The resulting hydrolysates were analyzed by HPLC on an amino derivatized column and by fast-atom bombardment spectrometry (FABMS). The chromatographic behavior and spectral data ( 13C NMR and FABMS) of five positional isomers of trimaltosyl-βCD are described.

Monitoring, sampling, and automated analysis

Monitoring, sampling, and automated analysis

Isolation and structure elucidation of a novel adipokinetic hormone (Lom‐AKH‐III) from the glandular lobes of the corpus cardiacum of the migratory locust, Locusta migratoria

A new adipokinetic hormone (named Lom-AKH-III) was isolated from the glandular lobes of the corpora cardiaca of Locusta migratoria. At the N-terminus it is blocked by a 5-oxoproline (pyroglutamic acid) residue (less than Glu). After enzymatic deblocking, the amino acid sequence of the N-terminus was partly established by automatic Edman degradation to be [less than Glu]-Leu-Asn-Phe-Thr-Pro-. Fast-atom-bombardment spectrometry (FAB-MS) revealed that the new hormone is an octapeptide, which is amidated at the C-terminus, and has a relative molecular mass of 1072. Based on the FAB-MS data the complete sequence is less than Glu-Leu-Asn-Phe-Thr-Pro-Trp-Trp-NH2, which was confirmed by chemical synthesis. All characteristics from HPLC, FAB-MS and biological activity of the natural hormone and the synthetic peptide appeared to be identical. Although the structure of this new hormone resembles that of Lom-AKH-I (less than Glu-Leu-Asn-Phe-Thr-Pro-Asn-Trp-Gly-Thr-NH2), its amino acid sequence points to a completely different route for its biosynthesis, involving a third prohormone. High-[K+]-containing media can cause release of all three adipokinetic hormones in vitro. Interestingly, the new hormone is absent in another locust species. Schistocerca gregaria. Based on in vitro biosynthesis experiments the turnover for this hormone is very high, suggesting an important physiological function. Locusta migratoria is the first insect species in which three different adipokinetic hormones have been demonstrated.

Studies in cluster ion formation. Part III. Collision-induced dissociation of the cluster ions of tetraalkylammonium halide salts

The collision-induced fragmentation of the cluster ions of tetraalkylammonium halide salts observed in fast atom bombardment spectrometry is consistent with the elimination of neutral molecules and the degree of fragmentation depends on the salt concentration in the matrix. The collision-induced dissociation (CID) spectra recorded from different concentrations of salt solutions have been compared and the effect of concentration on the stabilities of the cluster ions is discussed. In addition, the influence of the cation and anion size on the CID of both negative and positive cluster ions has been studied and the occurrence of anomalous ion intensity regions explained.