A. B. Shipovskaya

Phase processes and energetics of spontaneous change in the dimensions of acetate fibers in nitromethane vapors

The phenomenon of cyclic change (elongation and contraction) in the dimensions of acetate filaments and monofibers in the vapors of nitromethane as a specific solvent is quantitatively described. An algorithm for calculating the energy characteristics of the deformation, including the specific work, is developed. The longitudinal viscosity is estimated according to the deflection of a horizontally stretched sample. It is shown that the stereomeric structure of the polysaccharide is altered in the process of cyclic change in the filament dimensions, as is confirmed by reversal of the sign of specific optical rotation. The resultant data are interpreted in terms of phase (amorphous vitreous versus liquid-crystal states) and conformational transitions.

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.

Preparation and Properties of 3D Chitosan Microtubes

The preparation of 3D chitosan microtubes from polymer solutions in citric and lactic acids by the wet and dry molding methods is described. The mechanism of formation of the insoluble polymeric layer constructing the walls of these microtubes is characterized. The microtubes obtained from chitosan solutions in citric acid are found to have a fragile porous inner layer. For those obtained from chitosan solutions in lactic acid the morphology, elastic-deformation properties, physicomechanical properties, and biocompatibility were assessed. These samples have smooth outer and inner surfaces with no visible defects and high values of elongation at break. The strength of the microtubes obtained by the dry method is much higher than in the case of the wet one. A high adhesion and high proliferative activity of the epithelial-like MA-104 cellular culture on the surface of our microtubular substrates in model in vitro experiments were revealed. Prospects of using chitosan microtubes as vascular prostheses are suggested.

Influence of Physical and Chemical Modification on the Optical Rotatory Dispersion and Biological Activity of Chitosan Films

The optical and bactericidal properties of acetic and basic chitosan films were studied. By the ORD technique, we found that these films differed in the values of their specific optical rotation and of their rotary and dispersive constants. A sign inversion of was observed when the acetic chitosan films were heat-treated. The bactericidal activity of the initial and dehydrated acetic films was analyzed, and their moisture content and optical and biological activities were compared.

Optical activity of the anisotropic solutions of cellulose acetates in mesophasogenic solvents

The optical activity of the cholesteric liquid crystalline phases of solutions of cellulose diacetate in nitromethane and dimethylsulfoxide was studied. These systems exhibited optical activity anisotropy (i.e. the value of the specific optical rotation [α] varied with the orientation of the specimen). The contributions of the isotropic component and the anisotropic components of [α] were identified. The harmonic decomposition of the anisotropic component identified the separate contributions from the primary and secondary structures of the polymer and from the supramolecular twisted helicoidal structure of the cholesteric phase.

Effect of molecular mass on the optical activity of chitosan

The optical activity of chitosan has been examined by the optical rotary dispersion method in a wide molecular mass range, beginning from low-molecular analogs of the monomer unit and oligomers. In the spectral range from 300 to 710 nm, all samples demonstrate smooth curves of the optical rotary dispersion. For the polymers and oligomers, these curves lie in the region of negative values of specific optical rotation [α], while for monosaccharides, these curves are in the positive region. High-molecular-mass samples are characterized by maximal −[α] values that are practically independent of molecular mass. For partially depolymerized samples with M < 2 × 105 and for oligomers, the smaller the molecular mass of the sample, the greater the decrease in the modulus of −[α]. The passage to D-glucosamine chlorohydrate and to N-acetyl-D-glucosamine is characterized by inversion of the sign of rotation and achievement of high +[α] values.

New information concerning spontaneous elongation of acetate fibers

The ability of acetate fibers to experience spontaneous changes in their linear dimensions under the action of vapors of aprotic, amphiprotic, and protic solvents, which are widely used in scientific studies and engineering practice, has been investigated. In the vapor phase of solvents that are able to produce the lyotropic LC phase in cellulose derivatives, the phenomenon of spontaneous elongation of fibers has been discovered. This phenomenon has been observed for both cellulose diacetate and triacetate yarns, and their elongation can achieve ∼ 120–180%. In some systems, one can observe the reverse process that represents a spontaneous contraction of the sample after its self-elongation in solvent vapor. To study the above phenomena, a well-known system based on cellulose acetate and nitromethane is considered to be a reference system. The phenomenon of spontaneous elongation is proposed for use as a test for estimating the ability of the (cellulose ether)-solvent system to experience LC ordering.

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.

Modification of cellulose acetates for preparing chiral sorbents

Modification of cellulose acetates via sorption-desorption of vapors of mesogenic solvents in which the polymer forms a lyotropic liquid crystal phase and of mixtures of these solvents with water leads to the formation of a new chiral structure of the polymeric sample. This is manifested in a significant change in the value and even sign of the specific optical rotation of the polysaccharide system. The sorbents based on cellulose acetates that have been modified by such treatment exhibit specific affinity for definite optical antipodes. When a racemic mixture of L- and D-isomers of amino acids is passed through this sorbent, it acts as a chiral filter owing to “steric recognition” of one of the enantiomers, so that the filtrate contains an optically pure product (isomer). The revealed effects served as a basis for the development of a new procedure for preparation of optically pure stereoisomers of chiral products.

Preparation of water-soluble chitosan derivatives by modification of the polymer in vapors of monobasic acids

Sorption of vapors of monobasic acids and of vapors over their solutions of various concentrations by high-molecular-weight chitosan was studied. The dependence of the degree of the vapor sorption by the polymer on the acid solution concentration, chitosan molecular weight, and sorption temperature was determined. Watersoluble chitosan derivatives were obtained. The hydrodynamic properties of aqueous solutions of the modified samples were examined.