Enzymatic carbon-carbon bond formation in water-in-oil highly concentrated emulsions (gel emulsions)

Water-in-oil (W/O) highly concentrated emulsions (gel emulsions) of water/C14E4/aliphatic hydrocarbon systems were investigated as reaction media for the aldolic. condensation of dihydroxyacetone phosphate (DHAP) with acceptor aldehydes such as phenylacetaldehyde (1) and benzyloxyacetaldehyde (2), catalyzed by D-fructose-1,6-bisphosphate aldolase from rabbit muscle (RAMA). Prior to any enzymatic reaction, both the formation and stability of the W/O gel emulsions in the presence of reactants were assessed. It was found that the aldehydes improved greatly the kinetic stability of W/O gel emulsions at 25 degreesC by decreasing the hydrophile-lipophile balance temperature (T-HLB) of the water/C14E4/aliphatic hydrocarbon systems. Interestingly, the stability of RAMA in W/O gel emulsions was improved by 7- and 25-fold compared to that in aqueous medium or conventional dimethylformamide/water 1/4 v/v mixture, respectively. It was found that the equilibrium yields and enzymatic activity depended on both the aldehyde partitioning between the continuous and dispersed phases and the water-oil interfacial tension. The highest enzymatic activities were achieved in W/O gel emulsion systems with the lowest water-oil interfacial tension. The equilibrium yield depended on the water-oil interfacial tension for the hydrophobic phenylacetaldehyde, and on the partition coefficient for the hydrophilic benzyloxyacetaldehyde. Optimum equilibrium product yields (65-70%) were achieved at either the lowest water-oil interfacial tension or partition coefficient values.