Study On Esterification Of Dissociative Alcohols Catalyzed By MOFs Immobilized Enzyme

Chiral secondary alcohols,as key intermediates and chiral auxiliaries,are widely used in agricultural chemicals,food additives,flavors,chiral drug synthesis and other fields,so it is crucial to obtain optical activity of secondary alcohols.Enzymatic resolution has been widely concerned in chiral resolution due to the advantages of high stereoselectivity,mild reaction conditions,wide application range,high splitting efficiency,and environmental friendliness.However,free enzymes are limited to further application in enzymatic resolution due to the inherent defects including poor tolerance,difficulty in separating from the product,and reuse.In view of the above problems,in this paper,immobilized enzymes based on metal organic frameworks（MOFs）were prepared for the resolution of chiral secondary alcohol enantiomers.A kinetic resolution system of stereoselective transesterification using Candida antarctica lipase A（CAL-A）as a biocatalytic catalytic 1-（2-methylphenyl）ethanol enantiomers（（R,S）-MPE）was constructed.The immobilized enzyme CAL-A@Ui O-66 was obtained through physical adsorption by fixing the CAL-A on the screened Ui O-66 carrier.The resulting material was characterized and applied to the kinetic resolution of（R,S）-MPE transesterification.The results showed that the catalytic performance of CAL-A was significantly improved after immobilization.Under the optimal reaction conditions of temperature 55℃,substrate ratio 1:6,enzyme dosage 40mg and reaction time 24 h,the ee_sand conversion rate of substrate enantiomer obtained by using CAL-A@Ui O-66 as catalyst were 98.72%and 56.76%,respectively.Under the same conditions,the ee_sand conversion rates obtained with CAL-A as the catalyst were 83.74%and 48.26%,respectively.The performance of the immobilized enzyme remained good during the first two cycles.After the fourth cycle,the ee_swas 52.29%and the conversion rate was 30.20%.Construction of a kinetic transesterification reaction system of 1-（4-bromophenyl）ethanol enantiomers（（R,S）-BPE）catalyzed with Pseudomonas fluorescens lipase（Lipase AK）as biocatalyst.The lipase AK was immobilized on the selected NH₂-Co-MOF carrier by the covalent linking method of EDC/NHS to prepare the immobilized enzyme AK@NH₂-Co-MOF,and the obtained material was characterized and applied to the kinetic resolution of（R,S）-BPE transesterification.The results showed that the catalytic performance of the enzyme after immobilization was significantly improved.Under the optimum conditions,BPE enantiomers were resolved by AK@NH₂-Co-MOF with conversion of 50.42%,ee_sof 100.00%and enantiomeric excess of product（ee_p）of 100.00%.AK@NH₂-Co-MOF has good recycling performance,and the catalytic capacity is partly retained after 5 cycles of reuse.NH₂-Co-MOF is promising for enzyme immobilization,and the prepared AK@NH₂-Co-MOF exhibits great potential for efficient biosynthesis of optically pure BPE.Construction of a kinetic transesterification reaction system of 1-（4-methoxyphenyl）ethanol enantiomer（（R,S）-MOPE）catalyzed by Pseudomonas cepacia lipase（Lipase PS）as biocatalyst.Although NH₂-MOF-5 as a support can significantly enhance the catalytic performance of lipse PS,its stability is poor.A new composite carrier NH₂-MOF-5@PEI was prepared by introducing a cross-linked polyacetylimide（PEI）core and bonding NH₂-MOF-5 on its surface.Lipase PS was fixed on the composite carrier by physical adsorption method to obtain immobilized enzyme PS@NH₂-MOF-5@PEI.The resulting materials were characterized and successfully applied to（R,S）-MOPE kinetic resolution.The results showed that the catalytic performance of the enzyme was significantly improved after immobilization.Combined with characterization analysis,which may be attributed to the fact that the immobilization process induced the crystal transformation of NH₂-MOF-5 on the surface of the composite carrier,and the encapsulation of the enzyme on the carrier improved the structural stability and environmental tolerance of the enzyme.The ee_s,ee_pand conversion rates obtained with PS@NH₂-MOF-5@PEI as catalysts were 100.00%,100.00%and 51.54%,respectively.After eight cycles of use,no loss of catalytic performance was found,and the related performance indexes were far better than NH₂-MOF-5 immobilized enzyme and free enzyme.