Geometric Microenvironment Of Enzyme And Catalytic Properties

The global sales of chiral pharmaceuticals have been increasing atabout13%annual rate over past few years. Nowadays, enzymes arewidely recognized for preparing optically active compounds. Reasonsaccounting for this popularity are (1) they are highly chemo-, regio-, andstereoselective,(2) they are environmentally friendly and can be carriedout under mild conditions, because of which less side reactions happen(viz. isomerization, racemization, epimerization, and rearrangement ofmolecules). However, in organic synthesis, most of wild enzymes havethe defects of poor enantioselectivity, limited substrate scope and so on.Therefore, recently, molecular biologists have effectively improvedenzymatic enantioselectivity by means of site-directed mutagenesis anddirected evolution and in the field of chemical and materials, researchershave improved enzymatic enantioselectivity to a certain extent by meansof tuning chemical microenvironment of enzyme.Herein, we modulate the geometric microenvironment of enzyme byassembling enzymes into pores or channels of mesoporous silica with differrent pore sizes and different mesostructures to improve enzymeproperties.The ordered structure of mesoporous materials werecharacterized by the measures of XRD, TEM, N2adsorption-desorption,and so on，and indicate we have successfully constructed2D hexagonalmesoporous silicas and3D cubic cagelike mesoporous silicas,and each ofthe two mesoporous silica structures contains three to four different poresizes. Enzymes assembled into differrent geometric microenvironmentcatalysis transesterification reaction in organic phase to synthesis an anti-depressant drug precursor. We have studyed geometric microenvironmentof enzyme how to influence its catalytic performance.1. geometric microenvironment and catalytic performance of BCLlipaseThe catalytic activity BCL assembled in the2D hexagonal meso-poroussilicas with pore size of7.9nm,which size of is the equivalent to thedimension of BCL lipase, is higher than the catalytic activity of BCLassembled in the2D hexagonal mesoporous silicas with pore size of9.8nm,and the catalytic activity BCL assembled in the2D hexagonal meso-porous silicas with pore size of7.9nm is the highest among assembledBCL.Trp fluorescence spectrum ananlysis indicates the microenvironmentof Trp from BCL assembled in the2D hexagonal meso-porous silicaswith pore size of7.9nm have increasing hydrophobicity. As a result, we come to an conclusion that geometric microenvironment of BCL lipaseimprove the hydrophobicity of the microenvironment of Trp from BCL,and the increasing hydrophobicity contributes to the catalytic activity. TheBCL assembled in a variety of different geometric micro-environmentmaintain a high stereoselectivity (ee>99%).2. geometric microenvironment and catalytic performance of PFLlipaseWe have a further study that geometric microenvironment of PFLlipase how to influence its catalytic performance. the lipase having thesimilar structure with BCL lipase. PFL lipase assembled in the3D cubiccagelike mesoporous silicas with the cage size of12.5nm has the highestcatalytic activity and is4times of catalytic activity of free PFL lipase.Trp fluorescence spectrum ananlysis indicates the microenvironment ofTrp from the BCL assembled have the increasing hydrophobicity.Because the structure of PFL is similar with the structure of BCL.wespeculate that geometric microenvironment of PFL lipase enhance thehydrophobicity of the microenvironment of Trp from BCL and result inthe improvement of catalytic performance.Through the characterization of ATR-FTIR spectrum, we annlysisthe content of the four main secondary structures elements of BCLassem-bled in different geometric microenvironment. we find geometricmicroenvironment can lead the refold of secondary structures of PFL. when the refold is below a certain degree, the catalytic activity ofassembled enzyme increases, and when secondary structures of PFLfurther to refold beyond a certain limit, the catalytic activity of assembledenzyme reduce.To sum up, the geometric microenvironment of enzyme can influen-ce the enzyme’s catalytic performance. Geometric microenvironment canaffect the enzyme three dimensional conformation to increased hydropho-bicity of Trp microenvironment and can make the secondary structureenzyme refold to some degreet to improve catalytic activity.