Effect of the Composition of an Esterification Mixture on the Acid Properties of Gel-Forming Phosphorylated Polysaccharides

The physicochemical and biological properties of hydrogels based on starch, dextran, and cellulose phosphates synthesized in orthophosphoric acid–tributyl phosphate–phosphorus(V) oxide and orthophosphoric acid–urea systems are studied. It is found the apparent first step ionization constants of phosphate groups lie in the range of 2.5–2.9 and are virtually independent of the nature of the initial polysaccharide, the means of esterification, and the concentration of functional groups. It is concluded that the differences between the potentiometric curves of the titration of weakly acidic groups are due to the presence of polysaccharide phosphates. Carbamate groups contribute to the formation of a more cross-linked structure of hydrogels, making it difficult to ionize phosphate groups in the second stage. It is established that gel-forming phosphorylated polysaccharides exhibit antitumor activity.