AGGREGATION, HYDROGEN-BONDING AND THERMODYNAMIC STUDIES ON BOC-VAL-VAL-ILE-OME TRIPEPTIDE MICELLES IN CHLOROFORM

Evidence for micelle formation of Boc-Val-Val-lle-OMe (Boc = tert-buty loxycarbonyl) tripeptide (1), in chloroform has been obtained from IR and Raman scatter fluorescence spectroscopies. The critical micelle co ncentrations (c.m.c.s) of this peptide, obtained by these techniques, correlate well. It has been found that the micelle formation of the pe ptide in chloroform is hindered by increasing temperature. The aggrega tion numbers of the peptide have also been determined to be almost ind ependent of temperature. The Delta(m)G(-), Delta(m)H(-), Delta(m)S(-) and Delta(m)C(p) values have been estimated. Results from the above th ermodynamic parameters indicate that the driving force for micellizati on of the tripeptide 1 in chloroform is entirely enthalpic in nature a nd the aggregates of the peptide in chloroform are ordered. The IR spe ctra of the peptide in the pre- and post-micellar regions were analyse d; 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 inc reased as a function of peptide concentration after attaining c.m.c.