Influence of the reaction medium on enzyme activity in bio-organic synthesis: behaviour of lipase from Candida rugosa in the presence of polar additives.
Lipase from Candida rugosa immobilized on Celite was employed as the biocatalyst in order to examine the effect of the reaction medium upon enzymic activity and selectivity. As the model reaction, transesterification between tributyrin and pentan-2-ol in iso-octane (2,2,4-trimethylpentane) was chosen. A small amount of water (0.05%, v/v) was added to the reaction medium. Enhanced transesterification yields and increased selectivity of the lipase could be obtained by manipulating the microenvironment of the catalyst. Addition of 0.2% NN-dimethylformamide allowed a 93% higher ester yield compared with that obtained when no extra addition was made. Under the same conditions, the ratio of the amount of transesterification product over the amount of hydrolysis product after 48 h, became 52% higher than the ratio determined in the absence of additives. It was concluded that addition of compounds that have low logP3 (P is the partition coefficient in the octanol/water two-phase system) values and high dielectric constant was advantageous in order to favour transesterification over hydrolytic processes.