With the advent of electrospray ionization, mass spectrometry has become an invaluable tool for the study of biological molecules, not
just in the analysis of complex mixtures, as in proteomics, but in the gas-phase structures and properties of the gas-phase biological ions.
Unfortunately, by its nature, mass spectrometry is not well-suited for the investigation of neutral states of biological molecules. An important
question for neutral biological molecules involves the gas-phase structures, and how they are influenced by solvent. For example, isolated
gaseous amino acids are generally predicted to have canonical structures, distinct from the zwitterionic structures encountered in the
In our work, we have developed an approach for investigating the canonical structures of amino acids, by using a robust charge center
remote from the amino acid moiety as in sulfonated phenyl alanine (PheSO3-). By using this approach, we have been able to show that the
dissociation of the gaseous amino acid occurs by loss of ammonia, and decarboxylation, the predominate process in condensed-phase, does not occur.
Ion spectroscopy confirms the canonical structure of the amino acid moiety, and that the dissociation of PheSO3- results in formation of
an alpha-lactone. PheSO3- can also be incorporated into peptides, allowing for the investigation of canonical dipeptides, including dipeptides
involving Gly and Pro. We compare their dissociation behavior with those of other peptides with charges on the sidechains, like HisAla.