A feasible approach to tune the interaction of chitosan with sodium dodecyl sulfate.

Interaction of binary chitosan/nonionic surfactant (NIS) system with sodium dodecyl sulfate (SDS) in aqueous solution is described using turbodimetry, light scattering, electophoretic mobility and cryogenic electron microscopy. The formation of insoluble CHI/SDS complexes is weakened with a decrease in molecular weight of chitosan and critical micelle concentration of NIS as well as with an increase in NIS concentration. Soluble chitosan/NIS complexes absorb SDS molecules until the charge of mixed chitosan/NIS/SDS complexes reaches a critical value that depends on chitosan molecular weight followed by aggregation of primary electrostatic complexes via hydrogen bonding to complex nanoparticles. In contrast to formation of asymmetric swarm-like structures in the binary chitosan/SDS system, the aggregation of complex nanoparticles in the ternary chitosan/NIS/SDS system occurs by a head-to-tail binding mechanism with formation of elongated filamentous microstructures. The finding can be promising for preparation of microbiologically stable pharmaceutical and cosmetic compositions and drug delivery systems containing mixed surfactants.

Molecular features of the interaction and antimicrobial activity of chitosan in a solution containing sodium dodecyl sulfate.

Molecular interaction of chitosan with sodium dodecyl sulfate (SDS) is a more complicated process than it has been imagined so far. For the first time it has been shown that the shorter chitosan chains are, the more preferably they interact with the SDS and the larger-in-size microparticles they form. The influence of ionic strength, urea and temperature on microparticles formation allows interpreting the mechanism of microparticles formation as a cooperative electrostatic interaction between SDS and chitosan with simultaneous decrease in the surface charge of the complexes initiating the aggregation of microparticles. It is shown that hydrogen bonding is mainly responsible for the aggregation while hydrophobic interaction has a lesser effect. Chitosan demonstrates a high bacteriostatic activity in the presence of SDS in solution and can be promising for preparation of microbiologically stable pharmaceutical hydrocolloids, cosmetic products and chitosan-based Pickering emulsions containing strong anionic surfactants.