Conformational determination of [Leu]enkephalin based on theoretical and experimental VA and VCD spectral analyses

Abstract

Conformational determination of [Leu]enkephalin in DMSO-d₆ is carried out using VA and VCD spectral analyses. Conformational energies, vibrational frequencies and VA and VCD intensities are calculated using DFT at B3LYP/6-31G* level of theory. Comparison between the measured spectra and the spectral simulations of the low energy conformations of the neutral species enable conformational determination of the molecule. In an earlier study, based only on VA spectroscopy, the results led to the conclusion that [Leu]enkephalin had only a single β-bend conformation of the neutral species in DMSO-d₆. The present work shows the importance of using VCD in addition to VA in determining the conformation of chiral molecules and which one of the examined three single β-bend structures is the most stable in DMSO-d₆.