Study of the Mechanism of Lipase-Catalyzed Methanolysis of Sunflower Oil in tert-Butanol and Heptane

Abstract

Objectives: tert-Butanol has been reported to be a novel reaction medium for lipase-catalyzed biodiesel production due to its ability to eliminate negative effects of excess methanol, yet the molecular basis has remained to be solved. Methods: In this study, we investigated the effect of tert-butanol on the mechanisms of biodiesel production catalyzed by two different immobilized lipases from Candida antarctica lipase B (Novozym 435) and from Thermomyces lanuginosus lipase (Lipozyme TL IM). For comparison, similar experiments were also carried out in heptane. Results: In tert-butanol, the ping-pong bi-bi mechanism represents the kinetic data of both Novozym 435- and Lipozyme TL IM-catalyzed reactions and no methanol inhibition of lipase activities occurs. On the other hand, in heptane, the kinetic model of Novozym 435- catalyzed reaction agrees with the ping-pong bi-bi with alcohol inhibition mechanism. Whereas the kinetic model of Lipozyme TL IM-catalyzed reaction obeysping-pong mechanism at low methanol (<= 200 mM); it shows ping-pong mechanism with alcohol inhibition at high concentrations of methanol (>= 300 mM). Conclusion: These results demonstrate that tert-butanol alters the mechanisms of lipase-catalyzed reactions, presumably by causing conformational changes on the enzyme structure, which also eliminates inhibition by methanol.