Kinetics Study of Vitamin A Precursor Synthesis by Immobilized Lipase-Catalyzed Regioselective Monoacetylation in n-Hexane

Abstract

Vitamin A is an essential nutrient element in animal and human growth, which is usually produced by partially acetylating and transforming retinyl diol. The lipase-catalyzed mono-acetylation can obtain pure monoacetate compared with the classical chemistry process. In the current work, the synthesis of vitamin A precursor of Candida antarctica lipase B catalyzed by regioselective monoacetylation of primary hydroxyl of diol in n-hexane was studied. The reaction rate could be described in terms of the Michaelis-Menten equation with a Ping-Pong Bi-Bi mechanism and competitive inhibition by both substrates. A kinetic model was developed, and the apparent kinetic parameters were calculated as: Vmax =8.45 mmol/ (L•h); K m, vinyl =0.997 mmol/L; K m, diol =161.28 mmol/L; K i, diol =287.32 mmol/L; K i, monoacetate=18.13 mmol/L; and K I, diol =427.40 mmol/L. The current study indicates a competitive enzyme inhibition of highly concentrated diol during lipase-catalyzed acetylation reaction. When the diol concentration in the medium was low, there was a good conformity between the experimental and simulated values with 4.73% average relative error.