PROTON MOBILITY IN PROTONATED AMINO-ACIDS AND PEPTIDES

The MD+ ions of a variety of amino acids and small peptides have been prepared using CD4 and (CD3)(2)CO as chemical ionization reagents. Usi ng tandem mass spectrometry the fragmentation reactions of these MD+ i ons have been studied, both those occurring unimolecularly on the meta stable ion time scale (CD4 CI) and those occurring following collision al activation ((CD3)(2)CO CI). The results show that the added DC has undergone extensive interchange (leading to H/D scrambling) with all l abile hydrogens including carboxylic hydrogens, hydroxylic hydrogens, amidic hydrogens and amino hydrogens. The results indicate that the pr oton added to amino acids and simple peptides is very mobile and sampl es all positions bearing labile hydrogens prior to fragmentation of th e protonated species. (C) 1997 Elsevier Science B.V.