The Construction And Catalytic Selectivity Mechanism Of Chiral Nanozymes

Nature enzymes are powerful catalysts for both chemical and biology applications.Nanomaterials with intrinsic enzymatic activity,named nanozymes,have attracted great interests because of their high stability,facile production,long storage time,low costs,and more resistant to biodegradation.However,the poor activity and selectivity of nanozymes compared with nature enzymes remains them from being perfect alternatives to natural enzymes.Thus,the development of new strategy for the design of nanozymes with high activity and selectivity is urgently desirable.In addition,the study of catalytic mechanism is also necessary for the design and development of nanozymes.Herein,inspired by the structure of nature enzymes,a series of chiral nanozymes are constructed and optimized,the mechanism for the catalytic selectivity of these nanozymes is also conducted.These nanozymes possess chiral amino acid as chiral selector and exhibit stereoselectivity to the reaction of specific enantiomer.The rational mimicking of the nature enzymes and the novel structure of nanomaterials endows these chiral nanozymes with higher activity or selectivity than nature enzymes.The main results are summarized as follows:1.Although various nanomaterials have been designed for biocatalysis,few of them can accelerate chemical reactions with high selectivity and stereocontrol,which remains them from being perfect alternatives to nature enzymes.Herein,inspired by the natural enzymes,an enantioselective nanomaterial has been constructed,with gold nanoparticles(AuNPs)as active centers,chiral cysteine(Cys)as selectors for chiral recognition,and expanded mesoporous silica(EMSN)as a skeleton of the artificial enzyme.In the oxidation of chiral 3,4-dihydroxy-phenylalanine(dopa),the nanozyme with D-Cys shows preference to L-dopa while the artificial enzyme with L-Cys shows preference to D-dopa.Subsequent calculation of apparent steady-state kinetic parameters and activation energies together with molecular simulation show that the different affinity precipitated by hydrogen bonding formation between chiral Cys and dopa is the origin of chiral selectivity.2.Rational design of chiral nanozymes is still facing a great challenge because previously reported chiral nanozymes have suffered from their much lower activity compared with natural enzymes.Herein,inspired by natural enzymes and the superior structure of covalent organic frameworks(COFs)materials,a chiral COFs nanozyme with high activity and selectivity is designed,with iron 5,10,15,20-tetrakis(4’-tetraphenylamino)porphyrin(Fe-ATPP)in the backbone as the active center and the incorporation of L-histidine(L-His)as the binding site for chiral recognition.The well-dispersed Fe-ATPP endows COFs nanozyme with high peroxidase-like activity.The subsequent modification of L-His units can dramatically enhance the enzymatic activity up to 21.7 times higher than natural horseradish peroxidase(HRP).The incorporation of L-His units also endues COFs nanozyme with selectivity for L-dopa in the oxidation of dopa enantiomers,while replacing the L-His with D-His can reverse the preference to D-dopa.The activity and selectivity of COFs nanozyme can be optimized by varying the L-His content which can change the activation energy of the catalytic reactions and the substrate binding.Besides,the chiral COFs nanozyme shows general selectivity toward peroxidase-catalyzed enantioselective reactions.3.Compared with natural enzymes,it is still a great challenge to design a nanozyme with high enantioselectivity.Herein,we present an unprecedented approach to construct chiral artificial peroxidase with ultrahigh enantioseletivity.Based on the yolk-shell structure,a series of stereoselective nanozymes(Fe3O4@Poly(AA))are constructed by using the ferromagnetic nanoparticle yolk as the active center and amino acid-appended chiral polymer shell as the chiral selector.Among them,Fe3O4@Poly(D-Trp)possesses the highest enantioselectivity in the oxidation of chiral tyrosinol.More intriguingly,their enantioselectivity will be readily reversed by replacing D-Trp with L-Trp.The selectivity factor is up to 5.38,even higher than that of nature HRP.Kinetic parameters,dialysis experiments,molecular simulation together with activation energy reveal that the selectivity is originated from the D-/L-Trp appended polymer shell,which can result in better affinity and catalytic activity to D-/L-tyrosinol.The artificial peroxidases have been used for asymmetric catalysis to prepare enantiopure D-or L-enantiomer.Besides,by using fluorescent labelled FITC-L-tyrosinol and RhB-D-tyrosinol,the artificial peroxidase can catalyze green or red fluorescent chiral tyrosinol to selectively label live yeast cells among yeast,S.aureus,E.coli and B.sutilis cells.