Theoretical Design Of Spinel Nanozymes

Natural enzyme catalysis has high specificity and efficiency and thus has promising applications medicine,agriculture,chemical industry and food,etc.fields.However,natural enzymes have harsh requirements for reaction conditions and are inactivated under extreme p H,high temperature and other conditions,which greatly limits their applications.Therefore,researchers have been working on developing alternatives to natural enzymes.Nanozymes refer to nanomaterials that can mimic the catalytic function of natural enzymes.Compared with natural enzymes,nanozymes have the advantages of simple preparation,easy control of the composition and structure,low price,high temperature and p H stability.Besides,nanozymes inherit the optical,electrical and magnetic properties of nanomaterials themselves and thus become the hotspots in chemical,biological and environmental science.So far,at least more than 300 different nanomaterials such as metals,metal oxides,and carbon have been reported to have the catalytic function of biological enzymes.Spinel oxide is a low-cost catalyst that has attracted much attention in recent years.Spinel MFe₂O₄(M=Co,Mg,Ni,Cu,Zn)and Mn Co₂O₄ have been reported to possess peroxidase-like and catalase-like activities.Combined with their own optical,electrical,and magnetic properties,spinel nanozymes can be used to realize the multi-functional integration of catalysis,detection,imaging,etc.,and have broad application prospects in the fields of biology,medicine and the environment.However,the structure-activity relationship of spinel nanozymes is still not clear and the catalytic mechanism is rarely reported.The low catalytic activity and the poor substrate selectivity are the main challenges for spinel nanozyme development.Establishing a clear structure-activity relationship and developing activity descriptors that can be used for rational design and optimization of spinel nanozymes are key problems that need to be solved urgently in this field.Herein,using density functional theory calculation,we investigated the following issues:1)The influence of the location and type of metal cations on the geometry,electronic and magnetic structure of transition metal spinel AB₂O₄(A=Mn,Fe,Co,Ni,Zn;B=Cr,Mn,Fe,Co,Ni).The result indicates that the B cation in the octahedral O environment has significant effects on the electronic structure of the spinel,and the Jahn-Teller active ions Fe²⁺,Ni²⁺,Mn³⁺,Ni³⁺,Cr⁴⁺and Fe⁴⁺can significantly adjust the band gap and even change the conductivity.2)Three spinel surfaces including(100),(110)and(111)were constructed and their surface energieswere calculated.The calculated surface energies are in the order of₁₀₀<₁₁₀<₁₁₁ which indicates that the(100)surface is relatively stable and can serve as the catalytic reaction surface.3)The adsorption and dissociation mechanisms of H₂O₂ on the(100)surface of spinels were investigated and their POD-and CAT-mimicking activities and selectivities were predicted.The adsorption energy of hydroxyl(E_ads,OH)was proposed as a descriptor to predict the POD-and CAT-mimicking activities for spinel nanozymes:when E_ads,OH>-2.2 e V,spinel has selectively high CAT-like activity;when E_ads,OH<-2.2 e V,spinel has selectively high POD-like activity.The above results predict for the first time the underlying molecular mechanisms responsible for the POD and CAT activities of spinel nanozymes,and clarify the chemical nature that the E_ads,OH can be used as a descriptor for POD and CAT activities.The understanding of the catalytic principle can provide theoretical guidance for the rational design and synthesis for spinel nanozymes.