Formation, structure, properties of chitosan aspartate and metastable state of its solutions for obtaining nanoparticles

Abstract

Chitosan (200 kDa) dissolution in an aqueous solution of L-aspartic acid, physicochemical properties and features of the resulting chitosan salt were studied by conductometry, potentiometry, viscometry, turbidimetry, IR and NMR spectroscopy, and X-ray diffractometry. Chitosan aspartate is a water-soluble hydrated polymorph exhibiting properties of a cationic polyelectrolyte with an effective macromolecular coil radius 60–75 nm. The specific conductivity, dielectric constant, viscosity and pH of the chitosan – L-aspartic acid – water system change over time after preparation due to counterion-polycation association to form ion pairs, multiplet structures, and their subsequent aggregation. As a result, nanoparticles (40–90 nm) are formed after ~24 h, microparticles (0.6–1.4 μm) are after ~48 h, and precipitation occurs after 72–96 h. The precipitated phase is a water-insoluble chitosan salt with a developed system of H-bonds and high crystallinity degree. Chitosan nanoparticles have high biocompatibility and the ability to accelerate the proliferative activity of epithelial cells. HypothesisIon pairs and multiplets are formed in the chitosan – L-aspartic acid – water system due to counterion association, which leads to phase segregation of the polymer substance at the level of nanoparticles and microparticles.