Examination of ligand-ligand interactions by fast atom bombardment mass spectrometry

Abstract

The fast atom bombardment mass spectra of mixtures of peptide ligands exhibit well-defined peaks corresponding to protonated molecular Ions of ligand complexes. Quantitative selectivity in complex formation between ligands is indicated. A split-probe-tlp experiment has been designed in which individual ligand solutions are placed one on each half of the probe tip and exposed simultaneously to the atom beam. In systems where complexatlon requires interaction at several sites, no protonated complex formation is observed under these conditions. Complexes formed by simple single-site ionic Interactions, on the other hand, are readily formed in this system. The data suggest that complexatlon Is, at least in part, the result of solution (or possibly selvedge-induced) interactions as opposed to a vapor-phase phenomenon.

Molecular recognition and supramolecular chemistry in the gas phase

“…Several studies have addressed the possibility of saltbrigded structures in solvent-free environment and the related question of the formation of gaseous zwitterions-a question of vital importance for mass spectrometric experiments the aim at the secondary and tertiary structure of proteins or even non-covalent complexes between the peptide or protein and a substrate (Michaud et al, 1990). Also, salt-bridge mechanisms have been invoked to explain the pathway of peptide fragmentation reactions in sodiated (Lee et al, 1998b) or multiply protonated peptides and in the inhibition of certain H/D exchange reactions (Lee et al, 1998a).…”

N‐Myristoylethanolamine–cholesterol (1:1) complex: first evidence from differential scanning calorimetry, fast‐atom‐bombardment mass spectrometry and computational modelling

“…In order to further investigate the interaction between NMEA and cholesterol, we carried out fast‐atom‐bombardment mass spectrometric studies. Due to the soft ionization technique employed, FAB‐MS is particularly suited for the investigation of complexes that are held by relatively strong hydrogen bonds [18–20]. FAB mass spectrum of a 1:1 (mol/mol) mixture of NMEA and cholesterol, prepared in the same manner as for the DSC studies, is given in Fig.…”

Evidence for the direct desorption of crown ether-metal ion complexes in liquid secondary Ionization Mass Spectrometry

“…Although an effort was made to eliminate the possibility for cross-contamination between the split tip for both experiments, the possibility of adsorption of a volatile ligand from one side of the split probe onto the adjacent liquid matrix, followed by sputtering back into the vacuum, could not be ruled out. A later divided probe experiment conducted by our group [21] described significant differences in the relative ion abundances of crown ether-metal complexes when comparing data from a split probe (alkali metal on one half and crown ether on the other half) with singleprobe (alkali metals are mixed with crown ether on a single probe) experiments. Adsorption of the crown ether solution, followed by sputtering of the mixed complexes would essentially be a mixed solution phenomenon.…”

“…In the three split-probe studies mentioned [19][20][21], the noncovalent complex ion abundance that originates from gas-phase interactions (split probe) were always considerably lower than those intensities that arise from mixed solutions on a single probe. The quantitative extent of gas-phase reactions could not be determined.…”