Synthetic applications of enzymes entrapped in reverse micelles & organo-gels

The reverse micellar medium consists of tiny water droplets stabilized by surfactants in a bulk water-immiscible, organic solvent. The solutions are optically transparent and almost any enzyme can be solubilized in reverse micelles without loss of its specific activity. Reverse micelles provide a unique microenvironment for enzymes to react with water insoluble or poorly water soluble compounds present in the organic phase. It is possible to use even multienzyme systems to carry out a sequence of transformations. The presence of surfactant in the medium helps to overcome diffusion resistance and enzymes entrapped in hydrophilic gels such as polyacrylamide or calcium alginate can also be used for biotransformation of hydrophobic substrates and recycled several times. The solubilization of gelatin in reverse micelles to form organogels and solubilization of microbial cells in water-in-oil microemulsions without loss of viability have opened up new possibilities. Entrapped enzymes in such organogels or 'gelozymes' can be used in organic solvents without the use of surfactant, simplifying the workup procedure. Enzymatic reactions requiring co-factors such as reduction with alcohol dehydrogenase and epoxidation with monooxygenase can be carried out with whole cells. This is review discusses various applications of enzymes entrapped in reverse micelles and organogels for resolution of amino acids, peptide synthesis, reduction of prochiral ketones, synthesis of glycerides and chiral intermediates useful in production of agrochemicals and pharmaceuticals. The possibilities of substrate isolation, surfactant reuse and enzyme recycling with the help of bioreactors are also discussed.