Micelle formation of Tyr-Phe dipeptide and Val-Tyr-Val tripeptide in aqueous solution and their influence on the aggregation of SDS and PEO–PPO–PEO copolymer micelles

The aggregation properties of Tyr-Phe dipeptide and Val-Tyr-Val tripeptide were studied in aqueous solution and in the presence of SDS and SDS–polymer environments using UV–visible, surface tension, fluorescence and circular dichroism (CD) techniques. Both the peptides formed micelles. The cmc values obtained for dipeptide and tripeptide are 2 × 10−5 and 4 × 10−5 M, respectively in aqueous solution at 25 °C. The presence of additives (SDS and polymer) hindered the micelle formation of peptides. The cmc values obtained by various methods are in good agreement with each other. Effect of peptides on the aggregation properties of SDS also was investigated. The cmc of SDS was decreased in presence of peptides and were reduced with increase in temperature. Using monophasic micellization concept, the association constant (KA) for the SDS–peptide mixed micellar systems was determined. Using biphasic model, the thermodynamic parameters viz; ΔG°m, ΔH°m and ΔS°m for SDS–water and SDS–peptide–water mixed micellar systems, the standard free energy for transfer of SDS from aqueous to peptide additive environments were estimated at various temperatures. These results suggest that the SDS is more stable in micellized form in the SDS–water–peptide ternary systems compared to the situation in the corresponding SDS–water binary systems.