The Au(n) cluster probe in secondary ion mass spectrometry: influence of the projectile size and energy on the desorption/ionization rate from biomolecular solids.

A Au-Si liquid metal ion source which produces Au(n) clusters over a large range of sizes was used to study the dependence of both the molecular ion desorption yield and the damage cross-section on the size (n = 1 to 400) and on the kinetic energy (E = 10 to 500 keV) of the clusters used to bombard bioorganic surfaces. Three pure peptides with molecular masses between 750 and 1200 Da were used without matrix. [M+H](+) and [M+cation](+) ion emission yields were enhanced by as much as three orders of magnitude when bombarding with Au(400) (4+) instead of monatomic Au(+), yet very little damage was induced in the samples.

252Cf-plasma desorption mass spectrometry analysis of lipids A obtained by an elimination reaction under mild conditions.

Lipids A are the hydrophobic domains of bacterial endotoxic lipopolysaccharides. Since they are responsible for most of the biological activities (both pathogenic and beneficial) of endotoxins, the characterization of their structure is crucial to the understanding of their mode of action. However, the inadequacy of existing methods for preparing certain lipids A has prompted us to devise a new, mild procedure which gives intact products.

Plasma desorption mass spectrometry of two synthetic sarafotoxins: side reactions and characterization of the intermediates.

Sarafotoxins (SRTXs) form a family of toxic and potent vasoconstrictor peptides of 21 amino acids and two disulfide bonds. They are present in the venom of the burrowing asp Atractaspis engaddensis. We have made two derivatives of the amino acid sequence of SRTX-b, one of the most potent isotoxins, in the solid phase.

Influence of sequence on the fragmentation of serine- and threonine-containing peptides in 252Cf-plasma desorption mass spectrometry.

The molecular weights of four linear synthetic peptides, fragments of a snake alpha-neurotoxin, were measured by 252Cf-plasma desorption mass spectrometry. The fragmentation phenomenon observed at the level of serine and/or threonine residue with a concomitant ion/fragment association is reported for a group of two peptides (B and D) in contrast with the group (A and C) in spite of the high ratio of serine and threonine, namely peptide A. The propensity for specific fragmentation of peptide D seems to be correlated to the repetitive sequence, (Gly-Ser)2.

Identification of dekamycin antibiotics.

Dekamycin was isolated from strain DK5 of Streptomyces fradiae, and purified by ion-exchange column chromatography. Excellent separation of N-acetylated derivatives of the antibiotic mixture was achieved by two different methods, flash chromatography and high-performance liquid chromatography. Mass spectrometry (252Cf plasma desorption mass spectrometry, fast atom bombardment) for the analysis of N-acetyldekamycins (neomycin B, neomycin C, neamine and ribostamycin) was mainly used to confirm the molecular weight of a structure deduced by 1H and 13C NMR analyses.