Synthesis, Characterization And Reactivity Of Model Ligands And Complexes For The Active Site Of Quercetin 2, 3-dioxygenase

Dioxygen activation for the purpose of biomimetic oxidations has received considerable attention, owing to the possible application in catalysts for bioremediation of aromatic waste recently. In this paper, we focus on this active area, aiming at getting insights into the catalytic role of Glu73, metal ion effects, electronic effects and steric effects of the ligands, and co-ligands effects on the structure and reactivity of Quercetin 2,3-dioxygenase.One new bis(6-methyl-2-pyridylmethyl)amine model ligand carrying ortho-benzoic acid derivative as the ligand sidearm (LH) has been designed, synthesized, and characterized by IR, UV-Vis, ESI/MS,1HNMR and melting point measurement.Six novel binary model complexes and five ternary model complexes M(â…¡) (M:Fe, Co, Cu and Ni) have been designed, synthesized, and characterized as the structural and functional models for the active site of Quercetin 2,3-dioxygenase. Our design of model ligands and complexes focus on both catalytic site and substrate binding site of the enzyme. The structure of complex 4 has been determined by X-ray diffraction, which exhibits a distorted octahedral geometry.The reactivities of the model complexes towards flavonol and dioxygen have been investigated by UV-Vis monitoring. The metal ion effects, electronic effects and steric effects of the ligands, co-ligands effects on the reactivity of the model complexes have been investigated. Although the structures of the model complexes are similar, the reactivities show notable differences. The conclusions of our study are as follows.Metal ion effects:with the same ligand, the reactivities of model complexes with different metal ions are quite different and in the order Cu> Fe> Co> Ni.Electronic effects:with the same ligand, the reactivities of model complexes with different ligands show notable differences and in the order L8H> L1H> LH.Steric effects:with the same ligand, the reactivities of model complexes with different ligands are quite different and in the order L1H> LH> L9H.Co-ligands effects:with the same metal ion and ligand, the reactivity of the complex with SO42- is much higher than the complex with OAc.