Abstract
Ionic liquids (ILs) as neoteric solvents and microwave irradiation as alternative energy source are becoming
two important tools for many enzymatic reactions. However, it is not well understood what properties
of ILs govern the enzyme stabilization, and whether the microwave irradiation could activate enzymes
in ILs. To tackle these two important issues, the synthetic activities of immobilized Candida antarctica
lipase B (Novozyme 435) were examined in more than twenty ILs through microwave heating. Under
microwave irradiation, enhanced enzyme activities were observed when the enzyme was surrounded
by a layer of water molecules. However, such enhancement diminished when the reaction system was
dried. To understand the effect of IL properties, the enzyme activities under microwave irradiation were
correlated with the viscosity, polarity and hydrophobicity (log P) of ILs, respectively. The initial reaction
rates bear no direct relationship with the viscosity and polarity (in terms of dielectric constant and EN
T ) of ILs, but have a loose correlation (a bell curve) with log P values. The enzyme stabilization by ILs was
explained from aspects of hydrogen-bond basicity of anions, dissolution of the enzyme, ionic association
strength of anions, and substrate ground-state stabilization by ILs.