Paul G. Wenthold
Purdue University, USA
Title: Mass Spectrometric Investigation of the Decomposition of Canonical Structures of α-Amino Acids
Biography
Biography: Paul G. Wenthold
Abstract
The decomposition of canonical structures of α-amino acids has been investigated by using charge remote fragmentation. Neutral amino acids in condensed-phase have zwitterionic structures and are non-volatile, which makes gas-phase studies difficult. Previously reported mass spec studies of amino acids generally utilize ionization (protonation, deprotonation, metallation) of the amino acid group. In this work, we describe studies of amino acids where the ionization occurs away from the α-amino acid moiety. Therefore, we report studies of para-substituted phenylalanine derivatives, where the substituents are either a sulfonate (SO3ï€) or trimethylammonium (NMe3+) group. For both ions, we find that the main dissociation pathway involves loss of ammonia to form an α-lactone. For the sulfonate, loss of ammonia is the only dissociation pathway, whereas loss of CO2 is also observed for the ammonium derivative, indicating an effect of charge polarity on the dissociation. The dissociation processes of the α-lactones have also been examined, and are also found to be dependent on the charge polarity, which is readily explained in terms of benzylic positive charge character in the decomposition transition state. We have also examined the effect of solvation on the dissociation, and found that while addition of a single water does not change the reaction, dramatic changes are observed upon addition of two solvent molecules, which indicates interaction between the solvent and the amino acid group.