Copper(II) and copper(I) complexes with an open-chain N4 Schiff base ligand modeling CuZn superoxide dismutase: structural and spectroscopic characterization and kinetics of electron transfer.
The structure of the complex [CuII(PuPy)](ClO4)2 (PuPy = L = 1,8-bis(2-pyridyl)-2,7-diazaoctadiene-1,7) and the structure of the corresponding copper(I) complex were determined. In CuIIL(ClO4)2, a model compound with CuZnSOD activity, the unit CuIIL2+ has a tetrahedrally distorted square-planar N4 coordination geometry. The copper(I) complex with L was found to be dimeric, (CuIL)2(ClO4)2.DMF (DMF = N,N-dimethylformamide). The binuclear unit (CuIL)2(2+) has a helical structure with two ligands L bridging the two copper atoms to provide tetrahedral N4 coordination of each copper(I). In solutions of (CuIL)2(ClO4)2.DMF, solvent-dependent dissociation occurs according to D reversible 2M (D = (CuIL)2(2+); M = CuILSx+; S = solvent). Stopped-flow spectrophotometry was used to determine the rate constants for the dissociation of the dimer D (kM) and dimerization of the monomer M (kD) for S = acetonitrile and DMF. Equilibrium constants Kdim = kM/kD were determined spectrophotometrically. In aqueous solution, the oxidation of the dimer (CuIL)2(2+) by CoIII(NH3)5Cl2+ and cis- and trans-CoIII(en)2Cl2+ follows a second-order rate law, rate = kox[(CuIL)2(2+)][Co(III)]. Data for rate constant kox and for the activation parameters delta H++ and delta S++ are presented. In DMF, the oxidation of (CuIL)2(2+) by CoIII(NH3)5Cl2+ occurs via the monomer CuIL(DMF)x+ and the dissociation of (CuIL)2(2+) becomes rate-controlling. The reduction of CuIIL2+ by RuII(edta)H2O2- was found to be too fast to be resolved by stopped-flow spectrophotometry. The kinetic results are discussed mechanistically in terms of the redox switch aspects of the system.
Lange
J
J
Institut für Anorganische Chemie, Technische Universität Darmstadt, Petersenstrasse 18, D-64287 Darmstadt, Federal Republic of Germany.
Elias
H
H
Paulus
H
H
Müller
J
J
Weser
U
U
D003300:Copper / Q000737:chemistry*; D019281:Dimerization; D004579:Electron Transport; D007700:Kinetics; D008024:Ligands; D008956:Models, Chemical; D010084:Oxidation-Reduction; D012545:Schiff Bases / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D013482:Superoxide Dismutase / Q000737:chemistry*
D008024:Ligands; D012545:Schiff Bases; D003300:Copper; D013482:Superoxide Dismutase