Vibrational spectra and conformations for chiral opiates in changing solvents

Abstract

Vibrational spectra for chiral isomers of the neuropeptide Dermorphin are measured and analyzed in different solvents using FT-IR, Raman spectroscopy and computational means. This is in order to understand the effect that different solvents have on the corresponding spectra of peptides with chiral (L,D) amino-acid isomers. The D-Alanine form of particularly Dermorphin is many times more potent than the L-Alanine form, which we attribute predominantly to the influence of the solvents. The solvents investigated are H₂O/D₂O, DMSO and chloroform. They were chosen due to their varied polarity. The study is an experimental complement to the theoretical studies of the structure of Dermorphin and its docking to the µ (mu)-Receptor. The conclusions about the restrictions of the conformational space and the dynamical degrees of freedom are being assessed by vibrational spectroscopy. The main results derived from the experimental spectra of Dermorphin L/D-Alanine in various solvents, is the pronounced difference between the chiral forms, especially seen in the water solvent due to the strong polarity shift resulting from mutating the second position of the peptide from an L- to a D-Alanine.

Keywords:

• Infra-red spectroscopy
• Fourier transform spectroscopy
• Raman spectroscopy