Esterification of hydrophobic substrates by lipase in the cyclodextrin induced emulsion reaction system

Cyclodextrin (CD), a doughnut-shaped molecule having a hydrophilic surface and hydrophobic interior, can form inclusion complexes with various hydrophobic guest molecules inducing them into the emulsion state. The CD-induced emulsion reaction system was applied to the esterification between the hydrophobic oleic acid as the carboxylic acid and n-butanol as the alcohol catalyzed by lipase. The rate and yield were substantially increased in the CD-induced emulsion reaction system. The optimal reaction condition and the kinetic constants of the esterification reaction were determined. The enhancing mechanism was investigated through comparing the microscopic observation of the reaction mixtures, the inclusion complex formability, and the distribution of substrates, product and lipase at aqueous phase and CD-induced water immiscible phase in the CD-induced emulsion reaction system. The increase seems to have been caused by three reasons, the increased accessibility of lipase due to the emulsion formation, the shift of the equilibrium to the product formation side through the decrement of the affinity of butyl oleate with lipase, and the activation of lipase adsorbed on interface of oil-droplets in CD-induced water immiscible phase.