Kinetic aspects of ultrasound-accelerated lipase catalyzed acetylation and optimal synthesis of 4'-acetoxyresveratrol.

Ultrasonic assistance of lipase (Candida antarctica; Novozym (R) 435) catalyzed synthesis of 4'-acetoxyresveratrol from resveratrol and vinyl acetate was investigated. Response surface methodology and a three-level-three-factor Box-Behnken design were adopted to evaluate the effects of synthesis variables, including reaction time (4-12 h), enzyme amount (2500-4500 PLU), and ultrasonic power (90-150 W) on the percentage molar conversion of 4'-acetoxyresveratrol. Based on ridge max analysis, the optimum conditions for synthesis were: reaction time 10.78 h, enzyme amount 5492 PLU, and ultrasonic power 147.8 W. With ultrasound assistance, not only the phenolic compound acetylation time decreased, but also a high yield (95.2%) was achieved. The reaction kinetic model agreed with Ping-Pong mechanism, and the apparent kinetic constant V'(m)/K-2 ratio related to enzyme performance was 2.4 times higher in the ultrasound-assisted reaction than in the mechanical-mixing reaction. The apparent kinetic constant K-2 indicated that ultrasound enhanced the vinyl acetate affinity to the enzyme. The simplified Ping-Pong kinetic model was employed to simulate 4'-acetoxyresveratrol production in batch reaction. It was found that a good prediction existed between the fitting results and the experimental data. (c) 2012 Elsevier B.V. All rights reserved.