The origin of enzyme deactivation in ILs was studied by comparing enzyme activity in different ILs. The effect of IL chemical composition, structure, and

functionalization were studied to design new ionic liquids suitable for cellulose dissolution and cellulase activity. It was found that ionic liquids with a higher molecular weight would maintain enzyme (lipase) activity at a high level. Adding a longer alkyl chain on the imidazolium cation would accomplish that, but this would lead to a higher viscosity, which has a negative effect on cellulose disso­lution. To reduce the viscosity, the long alkyl chain was substituted by oxygenated chains, such as poly(ethylene glycol) and poly(propylene glycol). A long oxy­genated chain reduced the cellulose solubility, so an optimum chain length was determined to maintain both the cellulase activity and cellulose solubility high. The imidazolium cation with the best overall performance was derived from tri­ethylene glycol monomethyl ether. The oxygen atoms introduced are believed to form hydrogen bonds with cellulose, facilitating its dissolution. Adding a longer alkyl or oxygenated chain on the other side of the imidazolium cation led to a significant decrease in cellulose solubility, which was attributed to the reduction of hydrogen bonding with cellulose due to steric hindrance. The acetate anion led to higher cellulase activity and cellulose solubility than the chloride anion [135].