Novel self-aggregates of chitosan oligosaccharide grafted stearic acid: preparation, characterization and protein association.

A novel hydrophobically modified chitosan oligosaccharide (CSO) containing 5.4 stearic acid (SA) groups per 100 anhydroglucose units was synthesized by an 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC)-mediated coupling reaction. The purified copolymer was structurally characterized by IR spectroscopy. Characteristics of self-aggregates of the amphiphilic copolymers were studied by fluorescence spectroscopy and dynamic light scattering. The critical aggregation concentration (cac) value of the self-aggregates in aqueous solution was determined by measuring the fluorescence intensity of pyrene as a fluorescent probe. Mean diameter of self-aggregates in pH 7.0 PBS was 25.0 +/- 14.7 nm with a unimodal size distribution. The diameter, as well as the zeta potential of self-aggregates increased when the pH value of dispersion medium decreased. Bovine serum albumin (BSA) was further enveloped in the interface of different single self-aggregate and formed nanoparticles. The size of BSA-loaded stearic acid modified CSO nanoparticles depended on the pH values of the dispersed aqueous vehicle, and the size diminished when the pH values of the dispersed aqueous vehicle decreased, whilst, the BSA encapsulation efficiency enhanced. The nanoparticles were characterized by Transmission Electron Microscopy (TEM). BSA release from stearic acid modified CSO nanoparticles decreased when the pH values of the delivery media decreased, in the range from 7.2 to 5.8.