Charge and Temperature Dependence of Biomolecule Conformations: K~+Tryptamine(H_2O)_(n=0=1)Ar_(m=0=1) Cluster Ions

摘要

In this report, we detail the role of charge and temperature on the conformation of tryptamine (Tryp)-an analogue of tryptophan and the neurotransmitter serotonin-and the Tryp-water complex. Seven of the nine tryptamine conformers have been experimentally observed. The minimum-energy structure, Gpy(out), locates the NH_2 group gauche with respect to the pyrrole ring and its lone pair oriented away from the π cloud. In the Tryp-water complex, only the Gpy(out) conformer is experimentally observed. As the natural environment for neurotransmitters and amino acids includes a relatively high potassium cation concentration (～150 mM intracellular), a more accurate model for conformer selectivity should consider electrostatic influences. As Williams and co-workers have demonstrated, the presence of a cation can significantly alter the conformation of a biomolecule. However, the exact conformations cannot be predicted a priori, as many can be close in energy, and in the cases of lysine and glutamine, the M~+(amino acid) structure was also alkali ion-dependent.