The structures and properties of anionic tryptophan complexes.

The physicochemical properties of [Trp-H] and [TrpCl] (n = 1, 2) have been investigated in a combined computational and experimental infrared multiple dissociation (IRMPD) study. IRMPD spectra within the 850-1900 cm region indicate that deprotonation is localized on the carboxylic acid moiety in [Trp-H] clusters. A combination of hydrogen bonding and higher order charge-quadrupole interactions appear to influence cluster geometries for all investigated systems. Calculated global minimum and low energy geometries of [TrpCl] and [TrpCl] clusters favour coordination of the halide by the indole NH. [Trp-H] and [TrpCl] exhibit additional π-π interactions between the heterocyclic side chains.