Biomimetic Study Of Acireductone Dioxygenase

Acireductone Dioxygenase(ARD)could activate molecular oxygen to catalyze the oxygenative ring-opening reaction of flavonol at mild conditions selectively and effectively,so recently the mimic of acireductone dioxygenase is a novel emerging hot topic in bioinorganic field.In order to get insights into the effects of metal ions and carboxylate group as well as the electronic substituent effects of ligand on the chemical functions and reactivity of ARD,the activation mechanism of dioxygen and substrate,and their relationship,herein we made a series of exploratory work and got some valuable and important conclusions as follows:(1)Two new model ligands Lpy((pyridin-2-ylmethyl)histidine),Lim(((1H-imidazol-4-yl)methyl)histidine))and have been designed,synthesized,and characterized by IR,UV-Vis,ESI/MS,1H-NMR and melting point measurement.(2)Synthesis of corresponding Fe-ARD and Ni-ARD ternary model complexes using model ligands and substrates(LM~Ⅱ(Ph-(4-R)COC(OH)COPh)(M~Ⅱ:Fe,Ni;R:Br,H,Me)and characterized by IR,UV-Vis,ESI/MS,~1H-NMR and melting point measurement.(3)The reactivity of the model complexes towards model substrates and dioxygen have been investigated by UV-Vis monitoring.Although the structures of the model complexes are similar,the reactivities show notable differences.The caboxylate effects,metal ion effects,electronic effects,and steric effects on the reactivity of the model complexes have been investigated.The conclusions of our research are as follows:(I)The ternary model complexes catalyzed the oxidation of the C1-C2 and C2-C3 bonds of the substrate to generate two molecules of benzoic acid and CO,which are consistent with the natural Ni-ARD enzyme reaction products,respectively,and well simulate the two natural ARDs.(II)The ternary model complex generates superoxide radicals in the presence of oxygen and the substrate becomes a triketo structure.The resulting triketone structure is then coordinated with the ligand bidentate,hydrogen peroxide and alkali react to generate hydrogen peroxide anion attack.C1,after the transfer of hydrogen protons,the generated oxygen anion attacks C3 to form a five-membered ring,and finally releases carbon dioxide to generate benzoic acid and substituted benzoic acid products through carbon-carbon bond cleavage.(III)When the substrates are the same,the reactivity of the iron model complexes is better than that of the nickel model complexes,the activity order is:Fe>Ni.(IV)When the metal ions are the same,when the substrate molecule is introduced into the donor group,the reaction rate becomes significantly faster,indicating that the reaction is rapidly controlled by a nucleophilic reaction.