Synthesis of pH-Responsive Natural Polymers

This proposal concerns the synthesis of pH-responsive polymers derived from natural polymers, which display variations in physical properties, such as solubility and swellability, depending on the pH of the medium and may be potentially useful for the oral delivery of drugs. Natural polymers (polysaccharides) such as Chitosan, Starch, and Cellulose have prospective pharmaceutical applications because of their low toxicity, biocompatibility, and exceptional biodegradability. However they may need to be further modified for some unique applications such as the oral administration of drugs. Among various approaches to modify the properties of polysaccharides, derivatization is a convenient method to add new chemical functionality with minimum degradation of their initial properties. For example, introducing polar functional groups such as carboxy (COOH) not only modifies the bioadhesive properties of these polymers but also leads to pH-sensitive response. In the present proposal, pH-sensitive polymers derived from Chitosan, Starch, and Cellulose with carboxy group will be prepared by coupling the hydroxyl (-OH) functional groups of the polysaccharides with the amino (-NH2) group of the selected amino acids (Glycine, Aspartic acid, Glutamic acid) and their pH-responsive behaviour or phase transitions will be compared as a function of pH. The pKa values of the selected amino acids are 2.34, 3.65, and 4.25, respectively, so it is expected that the modified polysaccharides will display pH-dependent solubility behaviour (insoluble under acidic conditions and soluble under basic condition) as a function of the specific amino acid used in their modification.