Solvent-dependent conformations of cyclic tetrapeptide. II

The solvent-dependent conformations of cyclo(-delta-Ava-L-Pro-)(2) were characterized by means of the H-1 and H-13 NMR, CD, and LR spectra. CD results in CH2Cl2, CH3CN, CH3-OH, and H2O indicated that the change in polarity of the solvent induces a reversible change in the conformation of cyclo(-delta-Ava-L-Pro-)a, revealed by the decrease of the negative peak near to 230 nm and then by the gradual appearance of a negative trough near to 210 nm. The NMR data in CD3Cl, CD2Cl2, CD3CN, and CD3OH confirmed that cyclo(-delta-Ava-L-Pro-)(2) has a C2 symmetric conformation consisting of all-trans peptide-bond backbones, in all solvents, and that the change in polarity of the solvent induces a difference in the rotational states of the Pro C-alpha-C=O single bond.