Simulated Physiological Ph Solution Of Rare Earth La <sup> 3 + </ Sup> Spectroelectrochemical Interaction With Catalase

The application of rare-earth fertilizers in the agriculture was firstly suggested by Chinese scientists.The large amount of the research results indicated that the rare earth elements can enter into plants and influence the properties of the plant protective enzymes,such as catalase(CAT),peroxidase(POD)and superoxide dismutase(SOD). However,its chemical mechanism is still not clear.The research reports in this field are very few because the investigation is difficult due to the high chemical activity, the structural complexity and the conformational flexibility of enzymes.In this thesis,CAT from bovine liver and the light rare earth ion,La³⁺were selected as the research targets.Using fluorescence(FL)spectroscopy,circular dichroism(CD),atomic force microscope(AFM),transmission electron microscopy (TEM)and the electrochemical technique,the effect of La³⁺on the electrochemical and bioelectrocatalytic performances,the conformation of CAT and the interaction mechanism of CAT and La³⁺in the imitated physiological pH solution were investigated.It would lay the strong foundation for understanding the interaction mechanism of the rare earth ions and the protective enzymes in plants.The main results obtained are as follows:(1)A pair of obvious and nearly symmetric peaks appears in the cyclic voltammogram of CAT immobilized on the carbon nanotube modified GC electrode, indicating that the immobilized CAT could undergo a direct and quasi-reversible electrochemical reaction in 0.1 mol L^-1Tris-HCl buffer solution.The formal potential(E^0′)is -0.456V.The dependence of E^0′on the pH of the buffer solution indicated that the direct electrochemical reaction of the immobilized CAT involves one-electron and one-proton-transfer process.In addition,the immobilized CAT can retain its bioelectrocatalytic activity for the reduction of H₂O₂.(2)A pair of obvious and nearly symmetric peaks appears in the cyclic voltammogram of CAT immobilized on the gold nanoparticles(nanoAu)and cysteine (Cys)modified on GC electrode could undergo a direct and quasi-reversible electrochemical reaction in 0.1 mol L^-1Tris-HCl buffer solution.Its E^0′is -0.463V. The dependence of E^0′on the pH of the buffer solution indicated that the direct electrochemical reaction of the immobilized CAT involves one-electron and one-proton-transfer process.In addition,the immobilized CAT could retain its bioelectrocatalytic activity for the reduction of H₂O₂.(3)Low concentration of La³⁺could increase the orderly conformation of CAT and then increase the exposure extent of the electrochemically active center.Therefore, the direct electrochemical reaction of CAT would be promoted and the bioelectrocatalytic activity of CAT for the reduction of H₂O₂ would be increased. High concentration of La³⁺could decrease the orderly comformation of CAT through the strong interaction of La³⁺to N or O atoms in the peptide chain of CAT.It leads to the decrase in the orderly conformation of CAT and then the decrease in the exposure extent of the electrochemically active center.Therefore,the direct electrochemical reaction of CAT would be inhibited and the bioelectrocatalytic activity of CAT for the reduction of H₂O₂ would be decreased.