Chitosan functionalization with a series of sulfur-containing -amino acids for the development of drug-binding abilities

摘要

Chitosan (Chi; 0.5g) in 69.66mM aqueous acetic acid was mixed with 312.4mM methionine (methi) at 0.01mL/s to disperse and cause optimum collisions for supporting condensation reactions through NH2 of Chi and COOH groups of methi. The functionalized chitosan (f-Chi) product with methi developed an amide bond, which was represented as methi-functionalized chitosan [Chi-NHC(O)-methi]. Both the 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and Dean-Stark methods were followed for Chi functionalization. Sulfonation with chlorosulfonic acid in a dimethylformamide medium was conducted at 90 degrees C and 750rpm with an approximately 72% yield. The Chi-NHC(O)-methi was characterized by H-1-NMR spectroscopy and Fourier transform infrared stretching frequencies. The onset temperature of 280 degrees C recorded by thermogravimetric analysis/differential scanning calorimetry analysis, confirmed the high stability of the covalent bonds in Chi-NHC(O)-methi. The synthesis was repeated with other series members of sulfur (S) atoms containing -amino acids: homocysteine, ethionine, and propionine. The shielding of terminal CH3 was enhanced on elongation of the terminal alkyl chain in the case of propionine. The peak for the NH2 of Chi at a value of 4.73ppm shifted to 5.36ppm in Chi-NHC(O)-methi because of the involvement of NH2 in NHC(O). Theoretically, the value of NH2 of Chi was 5.11ppm, with a difference of 0.38ppm as compared to the experimentally determined value of 4.73ppm. Additionally, a new peak at a value of 3.26ppm also confirmed Chi functionalization. (c) 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46000.