ABSTRACT

Enzyme Activity ........................................................................... 91 3.14 Ionic Liquids (ILs) as Solvents ................................................... 91 3.15 Effect of Hydrophobicity of Ionic Liquid On Enzymes .............. 91 3.16 Effects of Cation and Anion Types of Ionic Liquids.................... 92 3.17 Biocatalysis in Mixture Solvents of Organic Solvent

and Ionic Liquid ........................................................................... 93 3.18 Summary ...................................................................................... 93

3.19 Review Questions ........................................................................ 94 Keywords ................................................................................................ 95 References ............................................................................................... 95

3.1 INTRODUCTION

The environment inside the cells is mixed, with hydrophilic in some parts and hydrophobic in other parts of the cell. Thus, enzymatic reactions outside the cell have been performed in buffered aqueous phase. One of the most challenging subjects of study in applied biocatalysis is the use of reaction media that are significantly less polar than water. The interest in the use of such nonconventional media has grown immensely after the recognition that biocatalysts such as enzymes, cell organelles and whole cells are active in all kinds of nonconventional media such as organic solvents, gases, and even supercritical fluids. The application of biocatalysts in these nonconventional media is very attractive in organic synthesis routes that desire the advantageous characteristics of biocatalysts such as high substrate specificity and that involve substrates and products that are poorly soluble in water. When water is one of the products of the synthesis reaction, the application of these media is even more attractive, because the equilibrium may be shifted in favor of the synthesis by lowering the water activity or by altering the partitioning behavior of the substrates and products between the relevant phases. Other reasons to justify the use of nonconventional media are [1]:

• Increased solubility of nonpolar substrates and products. • Shift in thermodynamic equilibria in favor of synthetic reactions. • Reduction in water activity leads to reduction of water-dependent

side reactions. • Reduction of substrate and/or product inhibition. • Enables manipulation of the stereo and regioselectivity of an enzy-

mic biocatalyst.