Peptide aggregates: a novel model system to study self-assembly of peptides

Ordered aggregates of Val-Leu-Pro-Phe, tetrapeptide 1, have been found in aqueous solutions. Evidence for the formation of aggregates for the above peptide was obtained by conductometric, pH metric, UV and fluorescence spectroscopic techniques. Values of critical micelle concentration (CMC) for the above peptide obtained by these methods are in good agreement with each other. The formation of organized aggregates of the peptide is favoured upon increasing the temperature (viz. the process of aggregation is endothermic). The aggregation number has been determined at different temperatures. Values of delta G0m, delta H0m, delta S0m and delta C0p have also been estimated. Binding studies with the 8-anilinonaphthyl sulfonic acid (ANS) and pyrene indicate that the interior of the aggregate is nonpolar. There are two processes with regard to the change of thermodynamical parameters like delta G0m, delta H0m, delta S0m, delta C0p and aggregation number (N). In the first process (from 5 degrees C to 40 degrees C) the driving force for aggregation seems to be the positive entropy because of water release due to intermolecular association of ionic moieties. The second process (from 40 degrees C and above) is due to intramolecular ionic interaction. The chemical shifts of the amide protons of the peptide have been presented in the light of inter- and intramolecular hydrogen-bond formation, and forces implicated in aggregation for both the first and second processes.