Synthesis of pH-Responsive Natural Polymers-Phase II

This proposal is the continuation of the previously approved project ?Synthesis of pH-Responsive Natural Polymers? (IG/SCI/CHEM/14/03) awarded in February 2014. Preliminary results demonstrated the success of the synthetic pathway for the synthesis of pH responsive polymer. Based on the preliminary results, technical support and supervision was provided to evaluate the synthesized products and writing undergraduate project report. However, writing manuscript for publication or conference presentation is in pending, as further investigations are required using different amino acid precursors and natural polymers (polysaccharides) such as Chitosan, Starch. Therefore, in order to reach a meaning full conclusion, further investigation on the preliminary results is purposed and will be conducted during 2017-19. This investigation required purchasing of different amino acids precursors, other reagents, consumable chemicals, research visit to the collaborator?s lab and possible conference presentation and publication. Summary of the previously approved project is restated here for review.Previous proposal was 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 previous proposal, it was proposed that pH-sensitive polymers would be derived from Chitosan, Starch, and Cellulose with carboxy group moiety and would 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 would 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. However only cellulose and glutamic acid were investigated (only synthesis) and their pH-responsive behaviour was barely investigated.The current proposal is concern the synthesis of pH-responsive polymers by derivatization of Starch, Chitosan, with other amino acids for example (Aspartic acid, Glycine) to produce both free carboxy group (-COOH) and amino group (-NH2) moieties and investigate their pH-responsive behaviour as a function of pH and compare the result with the previous finding.