A comprehensive study was performed on the supramolecular ordering and optical properties of thin nanostructured glycerohydrogel sol-gel plates based on chitosan L- and D-aspartate and their individual components in the X-ray, UV, visible, and IR ranges. Our comparative analysis of chiroptical characteristics, optical collimated transmittance, the average cosine of the scattering angle, microrelief and surface asymmetry, and the level of structuring shows a significant influence of the wavelength range of electromagnetic radiation and the enantiomeric form of aspartic acid on the functional characteristics of the sol-gel materials. At the macrolevel of the supramolecular organization, a complex topography of the surface layer and a dense amorphous–crystalline ordering of polymeric substances were revealed, while at the nanolevel, there were two forms of voluminous scattering domains: nanospheres with diameters of 60–120 nm (L-) and 45–55 nm (D-), anisometric particles of lengths within ~100–160 (L-) and ~85–125 nm (D-), and widths within ~10–20 (L-) and ~20–30 nm (D-). The effect of optical clearing on glass coated with a thin layer of chitosan L-(D-)aspartate in the near-UV region was discovered (observed for the first time for chitosan-based materials). The resulting nanocomposite shape-stable glycerohydrogels seem promising for sensorics and photonics.

A comprehensive study of the structure, properties and biological functionality of salt chitosan complexes with L- and D-aspartic acid (AspA) was carried out. It has been established that these polymer salts differ in their spatial organization, chirooptic characteristics, surface charge and macrocoil size. In experiments in vitro on a wide range of biological objects (unicellular algae, planktonic crustaceans, aerobic bacterial microorganisms, cell cultures and test plants), it was found that the chitosan salt with D-AspA exhibited the best biological activity. The results obtained confirm our hypothesis that the biological homochiral hierarchy principles are most consistent with the chitosan (D-aminoglycan) derivatives with the D-antipode of the acid.

The paper considers the formative processes of chiral nano- and microparticles in solutions of D-aminoglucan chitosan (CS) in L- and D-aspartic acid (AspA) by means of the counterionic condensation of components and the stabilization of particles by a polysiloxane shell. The effect of the L- and D-enantiomers of AspA on the structure, size, shape, and zeta potential of nano(micro)particles was studied using IR spectroscopy, dynamic light scattering, and electron and optical microscopy. It was found that chiral particles of CS·L-AspA and CS·D-AspA are non-toxic, hemo- and biocompatible, and exhibit high growth-stimulating activity in the test plants, with the best effect observed for homochiral D-glucan–D-AspA particles.

In the traditional method of removing excess acid used to obtain the salt form of chitosan, not only a reaction with neutralizing bases proceeds, but also partial deprotonation of macrochains. Since charged amino groups are responsible for the biological activity of the aminopolysaccharide, it seems important to develop methods for optimizing the acid–base composition of a chitosan-containing system without proton elimination. The paper presents the results of our study on the removal of non-stoichiometric aspartic acid from an aqueous dispersion of chitosan aspartate nanoparticles obtained by in situ self-assembly during counterion association on charged polymer chains and stabilized by a polysiloxane shell coating using isohydric and isothermal crystallization approaches. It is shown that a temperature decrease in the range of 50–4°C in combination with water distillation by 50–85% leads to supersaturation of the nanodispersion and crystallization of the poorly soluble component of the dispersion medium with precipitation. The influence of the acid/polymer molar ratio (1.3–1.7 mol/mol of NH2) in the target substance of the dispersed phase, the cooling rate (10 and 30°C/h) and the dispersion concentration degree (50–85%), as well as the temperature (22±2 and 4°C) and holding time (1–200 days) on the morphostructure, chemical composition, crystalline ordering and quantitative yield of the solid phase has been estimated. The correspondence of the air-dry form of the isolated precipitate to crystals of the zwitterionic form of aspartic acid has been proven by IR spectroscopy, X-ray structural analysis, dialysis, potentiometry and gravimetry. It has been found that the most optimal option for preparative removal of non-stoichiometric double bipolar ions is the concentration of nanodispersion by 85% followed by supercooling from 50 down to 4°C at a rate of 10°C/h. The developed approach to combining isohydric and isothermal crystallization of non-stoichiometric aspartic acid has been successfully tested on moderately concentrated solutions of the complex salt of chitosan hydrochloride–aspartate.

Chitosan (CS) with a viscosity-average molecular weight of 200 kDa and a deacetylation degree of 82 mol%, produced by Bioprogress Ltd. (RF) has been used in this work. Aqueous solutions of enantiomeric salt complexes of CS with L- and D-aspartic acid (AspA) have been obtained at an equimolar CS:AspA ratio, in terms of amino groups. Powders of CS·L-(D-) AspA salts have been isolated from the corresponding solutions by evaporation of water and stored in a desiccator at zero humidity. It has been established that under such conditions a water-soluble salt form of the polymer with lamellar light beige particles 0.05–1.0 mm in size is formed. Using the methods of elemental analysis, IR and NMR spectroscopy, and X-ray diffractometry, the chemical interaction of CS with L-(D-)AspA in aqueous solution and condensed state has been evaluated, and the chemical structure and supramolecular ordering of these enantiomeric salts have been studied. It has been established that, according to the classification of K. Ogawa et al., the formula unit CS·L-(D-)AspA corresponds to non-hydrated salts of type I, in which water molecules are replaced by acid anions. IR spectroscopy confirmed the donor--acceptor polymer–acid interaction and revealed a developed system of intermolecular and intramolecular contacts. One- and two-dimensional NMR spectroscopy showed the interaction of pairs of atomic nuclei between H3–H6 of the polymer and 2Hβ or Hα of the acid, H1 or H2 and Hα, H1 and H3–H6, due to the spatial proximity of protons in repeating monomer units, in the “bend” chain segments removed along the chain, and in neighboring macromolecules. For CS·L-AspA, additional resonances have been identified between H2 and H3–H6 of the polymer, for CS·D-AspA these have been between H1 or H 2. X-ray diffractometry has revealed a highly ordered orientation of macrochains and a high crystallinity degree, untypical for CS salts. The salt complex CS·D-AspA, in contrast to CS·L-AspA, is characterized by a smaller amount of crystallization water, a more ordered supramolecular structure, and a more developed system of intermolecular and intramolecular contacts.