SYNTHESIS AND PROPERTIES OF MODIFIED XANTHAN GUM

Xanthan gum is widely used as a stabilizing, emulsifying, thickening agent in pharmacology, medicine, food, oil, paint, textile, perfume, mining and agriculture. For food purposes, potassium, sodium or calcium salts of xanthan formed by carboxyl groups of glucuronic acid and pyruvate group are used. Currently, xanthan gum is not produced on an industrial scale in Russia. There are repeated attempts to create industries in various regions of the country. The paper synthesizes hydrophobized acetylated xanthan gum derivatives with different degrees of substitution. Physical-chemical and colloidal-chemical properties of initial and modified gum are compared by methods of viscosimetry, tensiometry, IR spectroscopy. The point of zero charge of xanthan gum is determined.. Change of macromolecule conformation depending on pH of aqueous solution and preliminary dewatering is shown. Delamination temperatures of initial and modified forms of xanthan gum were determined. The critical micelle formation concentration of the modified gum is 0.2%. At this concentration, the surface activity of the gum is 6.1 and 7.9 mJ m/kg when replacing two and five hydroxo groups, respectively. The possibility of using modified xanthan gum as a binder for obtaining fuel pellets with improved operational properties and calorific value is shown.

CONFORMATIONAL CONDITIONS OF CHITOSAN MACROMOLECULES AND THEIR INFLUENCE ON THE EFFICIENCY OF CHITOSAN POLYMERIZATION PROCESS WITH 2-HYDROXYETHYL METHACRYLATE AND N-VINYLPYRROLIDONE

Modification of chitosan with biocompatible synthetic polymers is important for the development of biodegradable medical materials with a tailor-made complex of properties. The issue of the influence of a polysaccharide macromolecule conformation on the synthesis and properties of the hybrid products remains acute. Conformational transitions of chitosan and their influence on the process of grafted polymerization of 2-hydroxyethyl methacrylate and N-vinylpyrrolidone onto the polymer and the properties of their copolymers were studied. To interpret the peculiarities of chitosan solutions properties, their viscosity was identified by the method of rotational viscometry; conformational transitions of the polymer polysaccharides were investigated by the method of spectrophotometry; dimensional characteristics of the polymer particles were assessed by the method of dynamic light scattering. Copolymers were characterized by the methods of IR-spectroscopy and gelpenetrating chromatography. Helix-coil conformational transition of the chitosan macromolecule was pH and temperature-sensitive. The effective size of the chitosan macromolecules for helix conformation was 14-35% larger than for the coil conformation. The grafted copolymer yield (98%) was significantly higher in the solutions of chitosan, where its macromolecules were in the coil conformation. The obtained results allow the researchers to create optimal conditions during the development of the copolymer-based biomedical materials with improved characteristics.

Light Scattering and Viscosimetric Studies on DNA after the Photoreaction with Some Furocoumarins

The light scattering measurements and the viscosimetric “i-assay” performed on native DNA solutions before and after irradiation at 3655 Å in the presence of furocoumarins show that the C4-cycloadditions of furocoumarins to the 5,6-double bond of the pyrimidine bases of DNA, which take place in the photoreactions, produce neither breakages of the polynucleotide chains nor relevant modifications of the macromolecule conformation.