Study On Preparation Of Immobilized Lipase Onto MOFs Support For Kinetic Resolution Of Arylpropionic Acid

Optically pure aromatic propionic acid and its derivatives are the key intermediates for the synthesis of a series of important chiral drugs in industry,and also have important applications in agricultural chemicals,food additives,spices and other industrial fields.At present,enzymatic kinetic resolution possess high stereoselectivity,mild reaction conditions and small pollution.However,several defects of free lipase,such as difficulty in recovery and recycle use,restrict industrial applications.Lipase immobilization provides a promise strategy for overcoming the above defects,which enhanced stability,good recyclability and probably improved activity.In this work,an aqueous system is established for enantioselective hydrolysis of aromatic propionic acid chiral compounds and MOFs is employed as the immobilized carriers for lipase to further investigated the resolution efficiency and applicability after immobilization.Immobilization of Candida antarctica lipase A（CAL-A）onto MOFs supports were investigated to enhance the efficiency of CAL-A in catalysis of an enantioselective hydrolysis reaction.CAL-A@ZIF-8 prepared through physical adsorption of CAL-A onto ZIF-8 was characterized by XRD,SEM,N₂adsorption/desorption analysis,TGA,and FT-IR,and further employed as the catalyzer in kinetic resolution of carprofen（CP）enantiomers through enantioselective hydrolysis of（R,S）-CP methyl ester.Results show that CAL-A is immobilized on ZIF-8 with a loading amount of 227 mg/g.Efficiency of CAL-A is significantly improved by employing CAL-A@ZIF-8,which is evaluated by the yield of（S）-CP（Y_S）and enantiomeric excess of the product（ee_p）,and the enhancement is ascribed for the hydrophobic nature of ZIF-8.The Y_Sof 90.62%and ee_pof 97.42%are achieved with CAL-A@ZIF-8,while only 59.79%of Y_Sand 92.61%of ee_pare obtained with free CAL-A under the identical conditions.Moreover,CAL-A@ZIF-8 possesses superior thermal stability and p H-tolerance than free CAL-A.In order to solve the problem of lipase recycling in adsorption method,the covalent linking method of lipase immobilization was studied.Lipase AYS was immobilized onto different metal-organic frameworks（MOFs）and diverse immobilization methods were compared.The immobilized lipase of AYS@UiO-66-NH₂via precipitation-crosslinking linkage method was characterized.Application of AYS@UiO-66-NH₂in kinetic resolution of 2-（4-Methylphenyl）propanoic acid（MPA）enantiomers by hydrolysis of the methyl ester of MPA was further investigated to test the application ability.In comparison to free lipase AYS,AYS@UiO-66-NH₂shows enhanced tolerance to p H and temperature.Moreover,after 4 cycles of reuse,no significant decrease in its initial activity was observed and the enantioselectivity was well retained.Under optimal conditions,the yield of（R）-MPA was 72.57%with 93.20%of enantiomeric excess,where good improvement of catalytic performance from free lipase AYS was successfully achieved.Water-soluble macromolecule polyethylene glycol（PEG）was used to modify the liapse molecules to improve the structural stability of the enzyme during the process of covalently linking.The immobilization of lipase using EDC and NHS functional agents can avoid the influence of GA on catalytic performance and specificity of the lipase.CAL-A as the aim catalyst was immobilized onto different metal-organic frameworks（MOFs）and diverse immobilization methods were compared.The immobilized lipase of PEG-CAL-A@UiO-66 via EDC/NHS covalent linkage method was characterized by XRD,SEM,N₂adsorption/desorption analysis,ELIASA,and FT-IR.Application of PEG-CAL-A@UiO-66 in kinetic resolution of 2-Phenylbutyric acid（PBA）enantiomers by hydrolysis of the hexyl ester of PBA was further investigated.The effects of temperature,substrate ratio,p H and reaction time on resolution effect were investigated.After 24 h reaction under the optimal conditions,PEG-CAL-A@UiO-66 shows excellent catalytic performance compared with the same amount of free CAL-A.Under the modification of PEG 400 and immobilization,the yield of（S）-PBA was 91.71%with 99.99%of enantiomeric excess.Additionally,PEG-CAL-A@UiO-66 possesses superior thermal stability and p H-tolerance than free CAL-A.After 3 cycles of reuse,no significant decrease in its initial activity was observed.