| H/D exchange reactions have been studied with the aim of developing methods for counting the number of active hydrogens of various classes of compounds. Such reactions of protonated aromatic amines and protonated amino acids and oligopeptides with ND$sb3$ have been carried out, in the gas phase, in the quadrupole collision cell of a hybrid BEqQ mass spectrometer.;In general, all active hydrogens of protonated aromatic amines are observed to exchange. In certain cases, however, the exchange of extra hydrogens has been observed. This has been determined to be partly due to the interchange of ring and amine hydrogens. The exchange of extra hydrogens is more significant for meta-substituted compounds whose ring- and N-proton affinities are similar. The extent of exchange has been found to be dependent on the site of protonation, which varies depending on whether the ion is formed in the solution phase (FAB) or in the gas phase (CI). Mechanisms for the exchange reactions are suggested. It is concluded that both the kinetic energy and the internal energy of the ions must be collisionally dissipated before reactive collisions occur.;Facile exchange of all active hydrogens has been observed for most amino acids, although certain exceptions have been noted. For example, the amino acids histidine, tyrosine, glutamine and asparagine did not exchange all active hydrogens with equal facility whereas protonated arginine underwent only limited exchange. Mechanisms for the exchange are proposed. All active hydrogens of protonated di- and tri-peptides whose residues consist of simple amino acids exchange readily. The extent of change is independent of the order of the amino acid residues within the di-peptides studied, except in the cases of Gly-Gln and Gln-Gly. Peptides of which arginine is a residue, however, do not exchange well.;The fragmentation channels followed by several protonated amino acids have been investigated through high energy (HE) and low energy (LE) collision induced dissociation (CID) studies, using the same mass spectrometer. Mechanisms for the fragmentation reactions are presented. |
