Mechanistic investigation of intracluster proton transfer from p- hydroxybenzoic acid to peptides

Abstract

The mechanism of photoinitiated intracluster proton transfer from the laser desorbed proton donor, p-hydroxybenzoic acid, to vari ous co-desorbed, non-chromophoric peptide proton acceptors has been investigated. Both laser power and wavelength-dependent data are presented which suggest a mechanism of cluster proton transfer initiated by two-photon ionization of the p-hydroxybenzoic acid. The mass spectra resulting from the photoinitiated cluster proton transfer reaction are shown to contain ion signals from both the protonated peptide parent molecule and peptide fragments. Examination of the specific fragment ions observed and fragment ions produced from a series of complementary dipeptide pairs suggests that the fragment ions result from peptide activation during the cluster proton transfer reaction. Furthermore, N-terminal protonation of the peptide proton acceptors is suggested in the absence of arginine or histidine residues.