Submitted to: Carbohydrate Polymers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 1, 2006
Publication Date: November 2, 2006
Citation: Biswas, A., Shogren, R.L., Stevenson, D.G., Willett, J.L., Bhowmik, P.K. 2006. Ionic liquids as solvents for biopolymers: acylation of starch and zein protein. Carbohydrate Polymers. 66:546-550. Interpretive Summary: In this work, we sought to find an inert solvent for biopolymers, such as starch and zein, so that they can be reacted in homogenous reaction media. This would enable us to improve the biopolymers properties by modifying them with many reagents that would have been impossible otherwise. To our knowledge, there is no prior report of the use of ionic liquid (IL) as solvent for starch and zein. ILs are a new class of non-volatile, non-flammable, non-toxic and environs friendly solvents. Our goal is to investigate the solubility and reactions of biopolymers in ionic liquid. We have found that biopolymers, such as starch and zein, are soluble in IL, 1-butyl-3-methylimidazolium chloride. Similarly, zein protein solution in ionic liquid reacted to give benzoate ester. In this work, we have demonstrated for the first time that IL could be used as a solvent for the chemical modifications to biopolymers. This IL method that we discovered would help the starch/zein ester manufacturers to prepare starch or zein acetate in an environment friendly way. IL could be recycled easily and this method eliminates the use of hazardous solvents.
Technical Abstract: Biopolymers such as starch and zein were found to be soluble at 80 deg C in ionic liquids such as 1-butyl-3-methylimidazolium (BMIMC1) and 1-buytl-3-methylimidazolium dicyanamide (BMIMdca) in concentration up to 10% (w/w/). Higher concentrations of biopolymers in these novel solvents resulted in solutions with too high viscosity to stir. Solutions of both starch and zein in BMIMC1 were acylated with anhydrides in presence of pyridine to give acetyl starch and benzoyl zein with various degrees of substitutions. Without pyridine the acylation reaction did not proceed. 1H NMR and IR spectroscopies were used to determine the degree of substitution of starch. Viscosity studies indicated that the starch underwent slight reduction in molecular weight during the course of acylation. Starch was also soluble in other non-conventional solvents such as choline chloride/oxalic acid and choline chloride/ZnCl2. However, zein was insoluble in these solvents.