Cellulase activity in imidazolium-based ionic liquids

Green alternatives to fossil-based fuels are very attractive and can be produced from cellulosic materials. Cellulose is the primary product of photosynthesis in plants and has immense importance as a renewable raw material. The production of biofuels starting from cellulose is gaining increasing attention and obviously implies the partial or total hydrolysis of cellulose: enzymatic processes are considered the most promising technology. Cellulases (EC 3.2.1.4) are the enzymes most commonly employed to selectively depolymerize cellulose in buffered aqueous solvents. Because of the very low solubility of cellulose due to its highly organized structure, enzymatic conversions proceed at very slow reaction rates. To improve the yield of fermentable monosaccharides, pretreatments of cellulose, such as thermal, chemical or physical treatment, have been applied to afford a better enzymatic conversion. Ionic liquids have been increasingly recognized as novel solvents for dissolution and pretreatment of cellulose. However, it was previously reported that ionic liquids efficiently solubilise cellulose but also often inhibit the enzymatic activity of native cellulases. The present study provides a useful comparison of the effect on stability and activity of four cellulases in two commercial imidazolium-based ionic liquids, namely 1-ethyl-3-ethylimidazolium diethylphosphate ([Emim][DEP]) and 1-ethyl-3-methylimidazolium acetate ([Emim][Ac]). The final aim of this investigation is to produce in one-step low molecular mass intermediates from cellulose, which could be successively used for further industrial modifications and/or applications.