Chiral epoxide production using mycobacterium solubilized in a water-in-oil microemulsion

The application of many biotransformation processes is limited because the substrates/products are poorly water soluble, can be further metabolized, or are inhibitory. Hence non-aqueous media (e.g. two-phase systems, low water environments) are being examined to determine whether they can be used to overcome these problems. One novel approach is to encapsulate whole cells in water-in-oil (w/o) microemulsions (reverse micelles). In this study we have investigated the influence of key system parameters on system stability and epoxidation activity of Mycobacterium M156 cells in reverse micelles comprised of a mixture of Tween 85 and Span 80 (10-20 w%, with an hydrophilic/lipophilic balance [HLB] of 10 and a weight ratio of Tween 85 to Span 80 = 5.7) in n-hexadecane. It was found that the minimum allyl phenyl ether (APE) concentration required in the bulk hexadecane solvent phase for epoxidation to occur was 15 mM, whereas the minimum molar ratio of water to surfactant (W(0)) was 35. The optimum epoxidation rate achieved was 3.8 nmol/mg dwt-min with an APE concentration of 50 mM, and a W(0) of 50, with an enantiomeric excess (ee) of 86%. However, epoxidation was found to terminate approximately 3 h after initiation, and the causes for this were postulated to be either: the deleterious effect of the solvent on the Mycobacteria; inactivation of the energy generating system; an insufficient energy supply, or; the instability of the monooxygenase enzyme. It was concluded that on balance emulsion systems are not an economically viable system for producing phenyl glycidyl ether (PGE).