Study On The Enzymatic Selective Synthesis Of Glycerides And Rule Of Acyl Migration In Ionic Liquids

Glycerides,such as monacylglycerol?MAG?,diacylglycerol?DAG?and triacylglycerol?TAG?are generally appilied in food,cosmetics and drug industries.Recently,organic solvent is one of important tools used in lipase-catalyzed synthesis of glycerides to selectively enrich single product.While compared with organic solvent,ionic liquids?ILs?has the advantage of lower saturated vapor pressure,good thermal stability and remaining liquid at room temperature.Especially its adjustable solvent properties hold promise of replacing organic solvent in lipase-catalyzed synthesis.In this paper,the direct lipase-catalyzed esterification of FFA and glycerol in ILs was studied to deduce the effects of ILs on selective enrichment of glycerides.And the optimization of synthesis reaction of MAG and DAG were studied respectively in different ILs.Finally,the influence of ILs on acyl migration kinetics of both DAG and MAG were investigated systematically.The main contents are as follows:Firstly,the correlation between IL properties and product selectivity or conversion was studied with the esterification of oleic acids and glycerol.EN T and Kamlet–Taft parameters were most likely the determining factors for glyceride selectivity.ILs with higher EN T and Kamlet–Taft values resulted in higher MAG content.ILs with higher log P and lower ? resulted in higher FFA conversion.ILs with higher log P,lower EN T and longer alkyl chains leaded to higher contents of TAG.High viscosity may reduce the reaction rate which could decrease the FFA conversion and change glyceride selectivity.Taking mole ratio into consideration,DAG could be selectively enriched in ILs with different polarity.All in all,ILs with higher polarity could lead to more content of higher polar glycerides.Secondly,the effect of FFA used as acyl donors on glyceride selectivity in ILs was studied.When same FFA was used as acyl donor,the effect of ILs on glycerides followed the rule of polarity.When different FFAs were used as acyl donors,the content of MAG and FFA conversion decreased with the increasing carbon chain length of FFAs.With increasing degree of FFA unsaturation,the content of MAG decreased and FFA conversionincreased,which would resulte in more content of DAG and TAG.Thirdly,[HO?CH₂?₂MIM]TF₂N was chosen as the solvent for selective synthesis of MAG.The optimal conditions were: reaction time 8 h,substrate molar ratio 4:1,lipase dosage 4%,ILs dosage 30%,temperature 50oC,4% activated 4? molecular sieves for removing water.Under the optimal conditions,conversion of FFA was up to 93.6% and MAG content was 61.1%.[MeO?CH₂?₂MIM]TF₂N was chosen as the solvent for selective synthesis of DAG.The optimal conditions were: reaction time 8 h,substrate molar ratio 1:2,lipase dosage 8%,ILs dosage 30%,temperature 60oC,4% activated 4? molecular sieves for removing water.Under the optimal conditions,conversion of FFA was up to 97.6% and DAG content was 70.3%.Lastly,the acyl migration kinetics of both 1,2-DAG and 2-MAG were determined in different ILs.Acyl migration was mainly influenced by EN T for most ILs.And basically,decreasing solvent polarity gave increase to acyl migration rate constants.However,it's not suitable for [HO?CH₂?₂MIM]TF₂N and [BMIM]N?CN?2 which have distinct basic substitute of cation?-OH?and basic types of anion?[N?CN?2]-?,both of them resulted in higher acyl migration rate.Therefore,acyl migration rate constants may also be influenced by the structure of ILs such as substitutes of cation and types of anion.