Charge and Temperature Effects on Hydrated Tryptamine Cluster Ions

Abstract

Infrared photodissociation spectra of M(+)(tryptamine)(H(2)O)(0-3)Ar(0-1) (M = Na, K) are presented here to demonstrate the role of charge and temperature in directing the conformation of tryptamine, a derivative of the amino acid tryptophan. All of the cluster ions discussed here are built from the two high-energy tryptamine conformers that have never been previously observed in neutral gas-phase studies. The Na(+) or K(+) provides a positive charge that stabilizes the Gpy(in) and Gph(in) conformers. DFT calculations are used to identify stable conformers and their corresponding harmonic vibrational frequencies in the CH, NH, and OH stretching regions, which aid in the interpretation of the experimental spectra. In some cases this interpretation is fairly straightforward by using the global minimum-energy structures. The more complex spectra associated with the argonated cluster ions suggest that high-energy isomers, trapped during the cluster ion formation process, are also present.