Synthesis, Characterization And Reactivity Of Model Ligands And Model Complexes For The Active Site Of Acireductone Dioxygenase

Dioxygen activation and biomimetic oxidation of carbohydrate is one of the most active areas, and have been received considerable attention recently. This work focus on this active area, aiming at getting insights into the catalytic role of Glu102, His98,metal ion effects, electronic effects and steric effects on the structure and reactivity of acireductone dioxygenase (ARD).Two new model ligands bis(2-pyridylmethyl)amine model ligand carrying para-methyl-ortho-benzoic acid derivative as the ligand sidearm L8H and (6-phenyl-2-pyridylmethyl)(2-pyridylmethyl)amine model ligand carrying ortho-benzoic acid derivative as the ligand sidearm L9H have been designed, synthesized, and characterized by IR, UV-Vis, ESI/MS,1H-NMR and melting point measurement.Six novel binary complexes M(II) (M:Ni, Fe, Cu) have been designed, synthesized, and characterized as the structural and functional models for the active site of ARD. Our design of model ligands and complexes focus on both catalytic site and substrate binding site of the enzyme. The structures of complex 3 and 6 have been determined by X-ray diffraction.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) With the same ligand, the reactivity of different metal ion model complexes show some differences and in the order:Fe> Ni.(II) With the same metal ion, the reactivity of para-CH3 substituted one is much lower than non-substituted one:L8H< L1H.(III) With the same metal ion, the reactivity of substituted by different bukyl groups are quite different and in the order:L9H< LH< L1H.(IV) With the same metal ion and ligands, the reactivity towards S2 is better than S1: S2> S1.The reaction products of model complexes towards model substrate S2 and dioxygen have been investigated by ESI/MS. The products of Ni(II)-complexes contain benzoic acid, while the products of Fe(II)-complexes containα-oxo-benzeneacetic acid. This results are consistent with the corresponding native Ni(II) and Fe(II)-ARD, just mimic to the catalytic reaction of native Ni(II) and Fe(II)-ARD.