O. N. Malinkina

Optical activity of solutions and films of chitosan acetate

The optical activity of solutions, oligomers, and films of chitosan acetate in a molecular weight (М) range of 660—640 000 g mol–1 was studied by the optical rotation dispersion method. Monotonic dispersion curves lying in the range of negative values of specific optical rotation [α] are observed for all samples in a wavelength range of 300—700 nm. The absolute value of [α] decreases as the degree of polymerization decreases for solutions of chitosan acetate. Three regions are observed on the dependence [α] = f(logМ): constant [α] values for solutions of highmolecular-weight chitosan samples, their relatively weak change for low-molecular-weight samples, and a sharp change for oligomers. The transition to the low-molecular-weight analog of the monomeric chitosan unit, d-glucosamine, is characterized by the inversion of the rotation sign as high positive values of [α] are attained. The nontrivial for high-molecular-weight compounds dependence [α] = f(logМ) was established for chitosan acetate films: the module of [α] of the films increases with a decrease in the degree of polymerization. It is shown that the module of optical activity of the studied samples is determined by the mobility of structural units of oligomer, polymer, or film. It is found by X-ray diffractometry that differences in optical activity of the solutions and films are due to restriction of the mobility of macromolecular segments during the formation of high-molecular-weight chitosan films and incomplete relaxation processes of film systems to the state of energetically favorable conformations.

Formation and pharmacological activity of silicon—chitosan-containing glycerohydrogels obtained by biomimetic mineralization

The biomimetic sol—gel synthesis of silicon—chitosan-containing glycerohydrogels was carried out using silicon tetraglycerolate as a precursor. It was found that chitosan accelerates gel formation in weakly acidic media. In more acidic media, the kinetics of the process changes according to the curve with a maximum, which can be attributed to different mechanisms of silanol condensation before and after the isoelectric point. The investigated silicon—chitosan-containing glycerohydrogels exhibit antibacterial, anti-inflammatory, and wound healing activity. The synthesized hybrid glycerohydrogels are promising materials for biomedical applications.

Optical activity of films based on chitosan of various molecular masses and modifications

The effect of chemical (polysalt → polybase reaction) and physicochemical (heat and vapor processing) modifications of the films of chitosan of various molecular masses and prehistories on the optical activity of the polysaccharide is studied. For both of the chitosan chemical modifications, the following dependence that is nontrivial for high-molecular compounds is established: [α] = f(log\({\bar M_\eta }\) ); as the degree of polymerization decreases, the modulus of [α] of the films increases. The X-ray diffraction study shows that the differences in the optical activity of the samples with different \({\bar M_\eta }\) are caused by a restriction in the mobility of the macromolecular sections upon formation of the films of high-molecular chitosan and incompleteness of the relaxation processes of the film systems to the state with energetically favorable conformations. The comparison of humidity and optical and biological activities of the initial and dehydrated chitosan films is performed. The chitosan films in the salt modification feature moderate bactericidal activity, which decreases with an increase in \({\bar M_\eta }\) of the polymer. The thermal processing of the salt modification reduces the antibacterial action; a conversion to the base form is accompanied by the loss of bactericidal activity.

Optical rotatory dispersion and circular dichroism of the films based on chitosan in the form of polysalts and polybases

The surface morphology and optical activity of films based on chitosan in different chemical forms were investigated by methods of scanning electron and atomic force microscopy, spectropolarimetry. These film samples are used as substrates for optical waveguides, sorption material and as substrates for cell culturing tissue-engineering and scaffold constructions. The essential differences in the structural and morphological relief of thin films from chitosan of different chemical forms are established. It was found that the spectra of optical rotatory dispersion and circular dichroism of films of chitosan in the form of polysalts and polybases are significantly different in absolute values of the optical rotation of the plane and circularly polarized light.

Investigation of the surface morphology of biocompatible chitosan-based hydrogels and xerogels

Our biocompatible hydrogel systems obtained by the sol-gel technqiue and based on chitosan and silicon polyolates are promising for medical and biological applications. The surface microrelief of these sol-gel materials (hydrogels and xerogels) based on chitosan and silicon tetraglycerolate was explored by AFM and SEM. A significant influence of the component ratio in the mixed system on the morphology and surface profile of the hydrogels and xerogels prepared therefrom was established. An increased content of the structure-forming component (chitosan) in the system was shown to increase the roughness scale of the hydrogel surface and to promote the porosity of the xerogel structure.

Influence of Chitosan Ascorbate Chirality on the Gelation Kinetics and Properties of Silicon-Chitosan-Containing Glycerohydrogels

The influence of the chirality of chitosan ascorbate on the gelation kinetics and the properties of hybrid silicon-chitosan-containing glycerohydrogels were studied with a deep estimation of the stereospecificity of chitosan polysalts with l- and d-ascorbic acid diastereomers and their biological effects. It has been established that l- and d-diastereomerically enriched chitosan ascorbates are characterized by a positive Cotton effect and differ in the wavelength of the maximum of the dichroic band (250 and 240 nm), as well as in the values of its specific ellipticity (21.8 × 105 and 39.2 × 105 deg·mL·dm−1·g−1), the sign of specific optical rotation (+ and −), the type of dispersion curves (anomalous and smooth), as well as the condensed phase morphology (anisodiametric particles with optical anisotropy and confocal domains of spherical shape, respectively). In the biomimetic sol-gel synthesis of silicon-chitosan-containing glycerohydrogels using silicon tetraglycerolate as a precursor, it was found that chitosan d-ascorbate retarded gelation. Thin congruent plates obtained from the corresponding glycerohydrogels based on chitosan d-ascorbate have higher mechanical strength and elasticity under uniaxial stretching and lower values of Young’s modulus. It has been shown that the systems based on chitosan d-ascorbate show the greatest antibacterial activity against Staphylococcus aureus 209P and Escherichia coli 113-13 and significantly promote the viability of normal human dermal fibroblasts. The results of our assessment of the biological properties of chitosan polysalts are unexpected, since ascorbic acid exhibits biological activity as its l-isomer only.

Optical properties of chitosan in aqueous solution of L- and D-ascorbic acids

The optical properties of aqueous chitosan solutions in L- and D-ascorbic acids were studied by optical rotatory dispersion and spectrophotometry. The specific optical rotation [α] of all chitosan solutions tested was positive, in contrast to aqueous solutions of the ascorbic acid enantiomers, which exhibit an inverse relationship of [α] values. Significant differences in the absolute values of [α] of the chitosan solutions at polymer-acid ratios exceeding the equimolar one were found.

Usage of cellulose acetate membranes for the sorption-luminescence determination of pyrene in aqueous media

The applicability of cellulose acetate membranes (CAMs) as a solid matrix for the luminescence determination of pyrene in aqueous micellar solutions is shown. The effect of the concentrations of various surfactants, namely, anionic sodium dodecyl sulfate (SDS), cationic cetyltrimethylammonium bromide (CTAB), and nonionic polyoxyethylene (10) mono-4-isooctyl phenyl ether (TX-100), on the fluorescence of pyrene in aqueous micellar solutions before and after sorption preconcentration and in an adsorbed state on a CAM has been studied. It has been found that the fluorescence intensity of pyrene on the solid-phase matrix increases as a result of pyrene solubilization in surfactant hemimiceles formed on the sorbent surface. The highest degree of pyrene extraction on CAMs has been achieved in the presence of cationic CTAB micelles. The CAM has a negative surface potential (−31.5 ± 2.5 mV), which affects the hydrocarbon recovery. The degree of extractlion and the polarity index of a microenvironment of pyrene molecules in solutions decrease in the order CTAB → SDS → TX-100.