Effects Of Ionic Liquids On Lipase Catalyzed Synthesis Of Amyl Caprylate In Nonaqueous Media

Enzymatic esterification in nonaqueous media has been widely used in foods, medicine and cosmetic industry. Regulation of solvent engineering is one of important tools in nonaqueous enzymatic catalysis. Ionic liquids, as one of new solvents for their unique properties, such as good thermal stability, special solubility, negligible vapor pressure and variable physical properties, especially its strong polarity hold the promise of regulating instrument in solvent engineering. In this paper, the role of ionic liquids in the synthesis of amyl caprylate catalyzed by lipase from R. miehi (RM IM) or from Candida Antarctica (Novozym 435) was investigated, assisted by microwave irradiation and conventional heating respectively. The main contents and results are as follows:1. The effect of [BMIM][PF6] on the initial reaction rate and reaction profile in the synthesis of amyl caprylate catalyzed by lipase RM IM in different organic solvents were studied. The trend of initial reaction rate with log P (2.0-5.1) in organic solvent in the presence of 1% [BMIM][PF6] was similar as that in organic solvent. The effect of [BMIM][PF6] on the reaction was only related to its addition rather than the solvent mixed with it.The fluorescence spectral analysis indicated that the conformational change coordinated to the change of enzyme activity. The initial reaction rate was decreased with the increase of the dosage of [BMIM][PF6] (1%-3% of caprylic acid, w/w) employed in the reaction in nonane. Further more, inhibition of different amount of [BMIM][PF6] on lipase RM IM was irreversible.2. The effects of [BMIM][PF6] on the optimum reaction temperature and operation stability of immobilized lipase RM IM were investigated. It was found that the optimum reaction temperature in nonane in the presence of 2% [BMIM][PF6] (60 oC ) was higher than that in nonane (50 oC ). Further more, the amount of 1% ionic liquid could improve operation stability of lipase RM IM.3. For ionic liquids with same cationic motie, the conversion of caprylic acid in nonane with 1% ionic liquid of PF6–was obviously higher than that in nonane with 1% ionic liquids of BF4–,Cl–. While for ionic liquids with same anionic motie, PF6–, the conversion of caprylic acid was decreased with the increasing of alkyl chain of imidazole ring. Microwave irradiation also improved the initial reaction rate in the presence of different ionic liquids.4. The effect of [BMIM][PF6] on the synthesis of amyl caprylate catalyzed by lipase Novozym 435 under microwave irradiation was studied. The effects of organic solvents with different log P and the addition of small amount of [BMIM][PF6] on reaction were investigated. The trend of initial reaction rate with log P (2.0-5.1) under microwave irradiation was similar as that under conventional heating in organic solvent. Microwave improved the lipase activity more obviously in polarer solvent. Addition of 2% [BMIM][PF6] didn't change the optimum water dosage (2% of caprylic acid, w/w). The initial reaction rate decreased first and then increased with the increase of the dosage of [BMIM][PF6](1%-8% of caprylic acid, w/w) in nonane under microwave irradiation. Applying the esterification in a ChemPower microwave reactor, microwave irradiation enhanced the reaction either in nonane or in nonane with [BMIM][PF6] (1% of caprylic acid, w/w).