Physicochemical properties of aqueous solutions of L-aspartic acid with and without addition of chitosan have been studied by conductometry, potentiometry, refractometry, tensiometry, and viscosimetry. It has been shown that aspartic acid molecules take a cyclic configuration stabilized by hydrogen bonds in aqueous solution at c > 0.04 g/dL (298 K). The interaction of chitosan with aspartic acid results in the formation of the polymeric salt that dissociates in aqueous solution to give chitosan polycation [~(NH₃)⁺] and aspartate counterions. The addition of chitosan to solutions of L-aspartic acid results in progressive increase in the surface tension, absorbance, and refractive index as well as the change in hydrodynamic properties of the macromolecules. The polymeric salt exhibits polyelectrolyte properties in dilute aqueous solutions. The increase in temperature impairs the thermodynamic quality of the solvent for chitosan leading to the shrinkage of the polymer coils and, hence, to the decrease in the intrinsic viscosity of the system.

Conditions for obtaining L-aspartic acid solutions of chitosan were considered: dissolution of the polymer with the formation of chitosan aspartate occurs in pH range of 3.6–3.8 at a minimum stoichiometric ratio of [acid]/[chitosan (−NH₂)] ∼ 0.43. The hydrodynamic, electrochemical, optical and biological properties of aqueous solutions of chitosan aspartic acid salt are investigated. It has been established that macromolecules of polymeric salt exhibit properties of a polyelectrolyte with a partially compensated charge in an aqueous medium. Huggins constants and temperature viscosity coefficients were calculated, which indicate an increased rigidity of the chitosan macrochain in the studied solutions and deterioration in the polymer—solvent interaction with increasing temperature. Chitosan aspartate powders in the form of lamellar microparticles with fractal ordering were isolated. Low biocompatibility and antibacterial activity of the polymeric salt are demonstrated, which allows recommending the production of biomedical products on its basis.