Influence of carboxyl anion on the dissolution of chitosan in cholinium-based ionic liquids

Abstract

Chitosan can be applied in because of its excellent antimicrobial activity and abundant bio renewable and biodegradable resource. To better utilize this kind of native polysaccharide, it is still necessary to develop an efficient chitosan solvent system. Tn present study, 6 kinds of novel choline carboxylate ionic liquids (ILs) were developed. The solubility of chitosan in these H2O-ILs with different molar ratio were measured at 25 °C. The effect of the carboxylate anion of the ILs on chitosan solubility was estimated and found that the solubility of chitosan in the H2O-IL increased with the increasing of alkyl chain length in the anion. Moreover, the H2O-IL solution would not able to dissolve chitosan because the proton H was alternated by employing NH2 or OH group. The H2O-[Ch][CH3CH2CH2COO] (Rmol=6:1) solvent system exhibits highly efficient capacity for the dissolution of chitosan, and the solubility of chitosan reached up to 20.8 wt.%. From NMR measurement, these results could be explained by the possible interaction between carboxylate anion and chitosan and the strong hydration of the carboxyl group in the IL, suggesting that anionic structure have a significant impact on the dissolution of chitosan in the H2O-IL solvent system. Altogether, these results would provide an important evaluation indicator for screening the most suitable solvent system of chitosan.