EXAMINATION OF LIGAND-LIGAND INTERACTIONS BY FAST ATOM BOMBARDMENT MASS-SPECTROMETRY

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-tip 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 complexation 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 complexation is, at least in part, the result of solution (or possibly selvedge-induced) interactions as opposed to a vapor-phase phenomenon. © 1990, American Chemical Society. All rights reserved.