Formation of modified chitosan/carrageenan multilayers at silica: Molecular dynamics modeling and experiments

Physicochemical properties of modified chitosan were determined by molecular dynamics (MD) modeling and various experimental techniques. Several parameters of primary significance were evaluated such as the molecule contour length and the equivalent chain diameter. The MD-derived interaction energies between the modified chitosan and kappa-carrageenan chains showed that the parallel (aligned) orientation is preferred compared to the crossed one. Measurements of the diffusion coefficient and the electrophoretic mobility enabled determination of the electrokinetic charge of the modified chitosan molecule, which remained positive for pH up to 10 ensuring a large stability of its solutions. This facilitated formation of supported films on silica composed of consecutive layers of modified chitosan and kappa-carrageenan monitored in situ by the streaming potential measurements. It was confirmed that the film terminated by the kappa-carrageenan layer was significantly more stable than the film terminated by the modified chitosan. This behavior was quantitatively interpreted in terms of the ion pair approach considering the discrete interactions between the macroion chains adsorbed in different layers of the film. The obtained results have practical significance for devising efficient procedures of biocompatible macroion film formation, which can serve as a platform for proteins and bioparticles immobilization and as capsule shells in various drug delivery systems and antibacterial food packages.