Self-assembly of the mixed systems based on cationic surfactants and different types of polyanions: The influence of structural and concentration factors

Abstract

Mixed systems based on cationic surfactants with a cyclic head group (morpholinium bromide (Mor-16) and triphenylphosphonium bromide (TPPB-16)) and pH-dependent polyanions with different natures (polyacrylic acid (PAA) and bovine serum albumin (BSA)) were formed. The critical aggregation concentration, sizes, zeta-potential, solubilization capacity, aggregation number of the mixed systems were determined by the complex of modern, complementary physicochemical methods. It has been shown that the nature of the polyanions and the head group of surfactant play important role in the formation of complexes. By several methods it has been shown that the addition of PAA to Mor-16 solution leads to a significant decrease in the CAC compared to single surfactant by one to two orders of magnitude, while the addition of fixed amount of BSA to Mor-16 system does not affect the aggregation threshold. For mixed PAA-TPPB-16 system only slight changes in CAC value compared to CMC of single TPPB-16 system were revealed by different techniques. The particle size in the mixed BSA-surfactant systems is about 10 nm, while in PAA-surfactant systems the size is determined by the nature of the surfactant head group. By the synchronous fluorescence method it has been shown that the interaction of BSA with surfactant occurred through the tryptophan residues of BSA. The presence of aromatic ring in the surfactant structure can be a key factor in increasing the binding efficiency in the surfactant-BSA systems.