Conformational flexibility in small biomolecules: tryptamine and 3-indole-propionic acid

A combined experimental and theoretical study is used to probe the conforma tional preferences of two flexible tryptophan analogs, tryptamine (TRA) and 3-indole-propionic acid (IPA). Resonant ion-dip infrared spectroscopy prov ides infrared spectra of single conformations of these molecules free from interference from one another. Density functional theory Becke3LYP calculat ions are used to predict relative energies for the conformers, while relaxe d potential energy scans determine the barrier heights separating the minim a. The different forms of the potential energy surfaces along the flexible coordinates for the two molecules provide a coherent explanation for the ob served conformational preferences. (C) 2001 Elsevier Science B.V. All right s reserved.