Kinetic Investigation Of Lipase-catalyzed Esterification In Non-aqueous Solvent

Lipase catalyze reactions is a new biosynthesis method in recent yeas. Compare withchemical process, lipase-catalytic method has the advantages of environmental protection andhigh efficiency. With more studies of enzyme-catalyzed esterification reaction in organicphase, more and more reports of reaction kinetics are also increasing. Many papers suggestthat the kinetics of enzymatic esterification agree with Ping-Pong Bi-Bi mechanism. Thisessay includes two aspects, researching the kinetics of lipase-catalyzed synthesis of oleic acidglyceride and L-ascorbic acid ethyl ester, respectively.First, we synthesize glyceryl oleate in organic solvent with oleic acid and glycerinum,immobilized lipase TLIM as catalyst. The mechanism and kinetic of this reaction are studied.The results showed that the reaction in acetone abides by the Mechaelis-Menten equation andfollows Ping-Pong Bi-Bi mechanism without inhibition by both substrates.Second, kinetics and thermodynamics of lipase-catalyzed synthesis of L-ascorbic acidethyl ester in acetone were investigated by using vinyl acetate as acyl donor. The resultsshowed that L-ascorbic acid could generate inhibition effect on lipase activity. A suitablemodel, Ping-Pong Bi-Bi mechanism having substrate inhibition, was thus introduced todescribe the enzymatic kinetics. Furthermore, the kinetic and thermodynamic parameterswere calculated from a series of experimental data according to the kinetic model. Theinhibition constant of L-ascorbic acid was also obtained, which seemed to imply thatenhancing reaction temperature could depress the substrate inhibition. Besides, the activationenergy values of the first-step and the second-step reaction were estimated to be37.31and4.94kJ/mol, respectively, demonstrating that the first-step reaction was the rate-limitingreaction and could be easily improved by enhancing temperature.