Aggregation, hydrogen bonding and thermodynamic studies on Boc-Val-Val-Ile-OMe tripeptide micelles in chloroform

Abstract

Evidence for micelle formation of Boc-Val-Val-Ile-OMe (Boc =tert-butyloxycarbonyl) tripeptide (1), in chloroform has been obtained from IR and Raman scatter fluorescence spectroscopies. The critical micelle concentrations (c.m.c.s) of this peptide, obtained by these techniques, correlate well. It has been found that the micelle formation of the peptide in chloroform is hindered by increasing temperature. The aggregation numbers of the peptide have also been determined to be almost independent of temperature. The Δ_mG^⊖, Δ_mH^⊖, Δ_mS^⊖ and Δ_mC_p values have been estimated. Results from the above thermodynamic parameters indicate that the driving force for micellization of the tripeptide 1 in chloroform is entirely enthalpic in nature and the aggregates of the peptide in chloroform are ordered. The IR spectra of the peptide in the pre- and post-micellar regions were analysed; there is no change in the intensity of the intermolecular hydrogen-bonding pattern for the peptide in the monomeric and micellar states. However, the intensity of the solvent-exposed —N—H stretching band increased as a function of peptide concentration after attaining c.m.c.