Structural and Functional Models for the Dinuclear Copper Active Site in Catechol Oxidases:  Syntheses, X-ray Crystal Structures, Magnetic and Spectral Properties, and X-ray Absorption Spectroscopic Studies in Solid State and in Solution

Abstract

Two novel tridentate dinucleating ligands containing benzimidazole were prepared, 1,3-bis(2-benzimidazolyl)-2-propanol (Hbbp, 1) and 1,5-bis(2-benzimidazolyl)-3-pentanol (Hbbpen, 2). Their complexing properties toward copper were studied in order to obtain structural and functional models for catechol oxidases. Syntheses and crystal structures of dinuclear Cu(II) complexes derived from these ligands are reported. [Cu(2)bbp(2)](ClO(4))(2).2MeOH, 3, crystallizes in the triclinic space group P&onemacr; with the following unit cell parameters: a = 7.702(3) Å, b = 10.973(6) Å, c = 12.396(6) Å, alpha = 100.59(4) degrees, beta = 99.02(4) degrees, gamma = 98.90(4) degrees, V = 998.7(8) Å(3), and Z = 1. [Cu(2)bbpen(2)](ClO(4))(2).3MeOH, 4, crystallizes in the orthorhombic space group Pccn, with the following unit cell parameters: a = 17.478(9) Å, b = 18.795(8) Å, c = 13.888(6) Å, V = 4562.2(4) Å(3), and Z = 4. Magnetic susceptibility measurements in the temperature ranges 4.6-459 K (3) and 4.6-425 K (4) indicate an antiferromagnetic coupling between the Cu(II) centers of both complexes. In order to determine the structures of the complexes in solution, XAS spectra (EXAFS and XANES) were recorded in the solid state and in solution. The interpretation of these data, including multiple scattering calculations, together with UV-vis titrations, shows that the complexes have the same structure in the crystalline state as well as in methanolic solution. Complex 4 is able to oxidize 3,5-di-tert-butylcatechol (3,5-DTBC) to the quinone (catecholase activity). This reaction was also studied by XAS and UV-vis spectroscopy. These measurements reveal the reduction of Cu(II) to Cu(I) accompanied by a decrease of the coordination number.

EXAFS studies on the active site of purple acid phosphatase from sweet potato Ipomoea batatas

“…The white line intensity of 1.4 and the position of the Zn-K-edge of 9663.6 eV suggest a five-to six-coordination by nitrogen and oxygen (Priggemeyer et al, 1995). The wide-shell filtered data were fitted using a curved wave approach with the program EXCURV92 (Binstedt et al, 1992;Binstedt et al 1992;Binstedt & Hasnain 1996) and constrained refinement of the imidazole groups including their multiple scattering contributions as described earlier (Zippel et al, 1996). one iron at a distance of 3.92 A.…”

Synthesis, structural characterization and catalytic activities of dicopper(II) complexes derived from tridentate pyrazole‐based N2O ligands

“…The Cu· · ·Cu distance of 2.988Å is comparable to the two Cu(II) ions apart in the oxidized state of the natural enzyme and to the Cu· · ·Cu distances in other model compounds. 1,12 Both copper centers are equivalent in the same coordination environment and so have only one type of metal configuration. Each copper atom is coordinated in a distorted square planar geometry by two pyrazole nitrogen atoms and two bridging alkoxo oxygen atoms.…”

“…The Cu· · ·O and Cu· · ·N bond distances [average Cu· · ·O = 1.908(4) and Cu· · ·N = 1.946(4)Å] are comparable to those of other dicopper complexes. 11,12 The deviation from a regular square is due to the steric force of the chelating ligand, which is induced by the phenyl groups on the pyrazole rings. Thus the two pyrazole rings of one ligand are folded to the back while the pyrazole rings of the other ligand are folded to the front.…”

Synthesis, Characterization of Novel Dinuclear Co(II)-Cu(II) Complexes and Investigation of Their Catecholase and Catalase-Like Activities

“…Some metal complexes have been used extensively for various purposes and also have received considerable attention as model compounds which mimic biofunctions such as the catecholase and catalase enzyme activity [2,3].…”