| Cu,Zn-SOD can effectively remove the superoxide anion free radical(O2·-)in the living body.But the natural Cu and Zn-SOD have the advantages of difficult extraction,high cost,short half-life and easy to be protease hydrolysis,difficult to pass through the cell membrane and allogeneic antigen and other shortcomings.Therefore,the functional simulation of Cu,Zn-SOD is an important way to develop exogenous chemicals that remove O2·-.The catalytic activity of the natural metal enzyme mainly depends on the the micro-environment which have important biological functions constructed by the amino acid residues in the vicinity of the metal coordination center.Utilizing nano or supramolecular assembly techniquethe,copper complex with catalytic properties and the groups with substrate recognition(such as amino group,guanidine group and quaternary ammonium group)were covalently / non-covalently coupled to nanoparticles(Au,CeO2 @ SiO2,Au@ SiO2 NPs,etc.),which has certain catalytic activity to construct the inorganic-organic composite system of nanoparticles-complexes was to simulate the function of Cu,Zn-SOD catalyzed the disproportionation of superoxide anion.In this paper,the effects of superoxide anion radical disproportionation by regulating the structure of the complex,the types and size of the nanoparticles,the guanidine group of the quaternary ammonium salt and the substrate,investigated the catalytic activity and the efficient superoxide anion free radical disproportionation.In addition,the activity of hydroxyl radical scavenging in some enzyme models and the hydrogenation of nitrophenol was studied.Specific research of this article includes the following parts:(1)The functions of Cu and Zn-SOD were simulated by the compositesystem of gold nanoparticles loaded with adamantane copper complex: Make the use of guanidine groups with positive charge can electrostatic identification of negatively charged substrate O2·-under the physiological pH condition,using the electron current carrying effect of gold nanoparticles with different particle sizes and the reversal conversion of oxidation redox potential of adamantane copper complexes to catalyze O2·-disproportionation.The gold nanoparticles(Au NPs)of about 4 nm and 15 nm were prepared by reduction of HAu Cl4 with potassium citrate and sodium borohydride,and6-mercapto-?-cyclodextrin was covalently coupled with Au NPs,then super-molecular assembly of adamantane copper complex1,(Cu L1Cl2,L1 = N,N'-bis(pyridine-2-methyl)amantadine),Designed and synthesized M1(~ 15 nm Au@?-CD?1),M2(~ 15 nm AuNPs@6-guanidyl-?-CD/?-CD?1),M3(~ 4 nm Au@?-CD?1)and M4(~ 4 nm Au@6-guanidyl-?-CD/?-CD?1).The models were characterized by IR,CV,SEM,TEM,XRD,EDS and ICP.The IC50 values of free radical anion disproportionation of model M1,M2,M3 and M4 were 0.172 ?M,0.141 ?M,0.153 ?M and 0.132 ?M,respectively,by using riboflavin-NBT light method.The SOD-like activity of M2 was increased by 18% was compared to M1,and M4 was increased by 13% was compared to M3.This may be due to the fact that guanidine is synergistically catalyzed by substrate recognition.In addition,the SOD activity of M3 and M4 is higher than that of M1 and M2,which may be due to the smaller particle size of M3 and M4,and the high specific surface area,thus enhancing the synergistic catalysis.(2)The functions of Cu and Zn-SOD were simulated by the composite system of CeO2@SiO2 nanoparticles loaded with Salen copper complex:Make the use of quaternary ammonium salt with positive charge can electrostatic identification of negatively charged substrate O2·-under the physiological pH condition,using Ce4+/Ce3+ with potential reversible conversion and copper complexes(2,CuSalen,Salen = salicylaldimine;3,CuSalenQA,Salen QA =(1'-methyl-2'-hydroxymethyl)5-imidazolylmethyl-salicylaldehyde imide)to catalyze O2·-disproportionation.Four complexes of nanocomposites were designed and synthesized: M5(SiO2@2),M6(SiO2@3),M7(CeO2@SiO2@2),M8(CeO2@SiO2@3).And them were characterized by SEM,TEM,XRD,IR,XPS,ICP and so on.The IC50 values of free radical anion disproportionation of model M5,M6,M7 and M8 were 0.235 ?M,0.205 ?M,0.161 ?M and 0.129 ?M,respectively,by using riboflavin-NBT light method.Among them,the catalytic activity of M8 has highest SOD activity than the M7 increased by 19%,SOD activity than the M5 increased by 37%,than M6 increased by 45%,which may be due to the synergistic catalysis of the cerium oxide nanoparticles with a potential conversion effect,while the positive charge of the quaternary ammonium salt side arm in the Salen copper complex can actually identify the O2·-substrate,thereby enhancing the SOD activity.(3)The functions of Cu and Zn-SOD were simulated by the composite system of Au@SiO2 nanoparticles loaded with Salen copper complex:Utilizing Au@SiO2 loaded nanocomposites Cu(II)salen complexes and using Au NPs loaded the complexes of 6-SH-?-CD ? 1,which modified amino groups and guanidino groups to construct complex nanocomposites to catalyze O2·-disproportionation.Five complexes of nanocomposites were designed and synthesized: M9(Au@Si O2@2),M10(Au@SiO2@3),M3(AuNPs@?-CD?1),M11(M3@SEtNH2,SEtNH2 = 2-mercaptoethylamine),M12(M3@SEnGuyl,SEnGuyl = 2-mercaptoethylguanidine).The models were characterized by IR,CV,SEM,TEM,XRD,EDS and ICP.The IC50 values of free radical anion disproportionation of model M9,M10,M11 and M12 were 0.225 ?M?0.188 ?M?0.131 ?M and 0.106 ?M,respectively,by using riboflavin-NBT light method.Then study the models catalyzing superoxide anion radical disproportionation,which its IC50 values were 0.225?M,0.188 ?M,0.153 ?M,0.131 ?M and 0.106 ?M,respectively.Among them,the SOD activity of M10 was about 16.4% higher than that of M9 because the positive charge of quaternary ammonium salt side arm of salen copper complex could electrostatically identify O2·-substrate,and thus enhanced SOD activity.The SOD activity of M12 was higher than that ofM11 increased by about 19%,compared with M3 increased by about 30.7%,which may be attributed to guanidine and mercaptoethylamine can be identified on the substrate and catalyze catalysis,thereby enhancing the SOD activity.(4)The properties of catalytic p-nitrophenol reduction were studied using models M5,M6,M7,M8,M9 and M10.The results show that M7,M8,M9 and M10 have better catalytic activity than M5 and M6 under the condition of n(p-NP): n(NaBH4)= 1: 200.The reaction rate constants of M7,M8,M9 and M10 were 3.2 × 10-3 s-1,4.15 x 10-3 s-1,6.9 x 10-3 s-1 and 14 x10-3 s-1.This may be due to the fact that the positive charge of the quaternary ammonium salt side arm in the Salen copper complex can actually identify the O2·-substrate,so that the reduction of p-nitrophenol can be catalyzed more quickly. |
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