BACKGROUNDDeep eutectic solvents (DESs) have recently attracted widespread interests as new green solvents for (bio)chemical transformations. In this study, 24 DESs were prepared to study their effects on enzymatic performance: two cholinium salts (ChCl and ChAc) combined with four H-bond donors (HBDs) (urea, glycerol, acetamide, ethylene glycol) at three molar ratios. RESULTSIn DES-containing aqueous solution, Penicillium expansum lipase (PEL) can be activated and stabilized up to 2.4 times and 18.4 times its original values, respectively. When DESs were used alone as the reaction medium to produce biodiesel from Millettia pinnata seed oil, Novozym 435 enabled a better conversion than PEL, with a maximal yield obtained in ChAc/glycerol (1:2). These DES effects arise from the formation of DES rather than from the synergetic action contributed by each of its components. Preliminary toxicity tests on Hydra sinensis suggest that a DES may be less toxic than its components. CONCLUSIONDESs are viable solvents/cosolvents for lipase-catalyzed reactions, and both lipase activity and stability are affected by the choice of DES components (salts and HBDs) and their molar ratios. In both reaction systems above, the ChAc-based DESs were superior to the ChCl-based ones, while glycerol showed better compatibility with lipase than the other three HBDs tested. (c) 2013 Society of Chemical Industry