| 17880209 |
Liu GF, Filipovic M, Heinemann FW, Ivanovic-Burmazovic I: Seven-coordinate iron and manganese complexes with acyclic and rigid pentadentate chelates and their superoxide dismutase activity. Inorg Chem. 2007 Oct 15;46(21):8825-35. Epub 2007 Sep 20.
The reactions of seven-coordinate [Fe (III)(dapsox)(H (2) O)(2)] ClO (4).H (2) O (1), [Fe (II)(H (2) dapsox)(H (2) O)(2)](NO (3))(2).H (2) O (2), and [Mn (II)(H (2) dapsox)(CH (3) OH)(H (2) O)](ClO4) 2 (H2O) (3) complexes of the acyclic and rigid pentadentate H (2) dapsox ligand [H2dapsox = 2,6-diacetylpyridinebis (semioxamazide)] with superoxide have been studied spectrophotometrically, electrochemically, and by a submillisecond mixing UV/vis stopped-flow in dimethyl sulfoxide (DMSO). The same studies were performed on the seven-coordinate [Mn (II)(Me (2)[15] pyridinaneN (5))(H (2) O)(2)] Cl (2).H (2) O (4) complex with the flexible macrocyclic Me (2)[15] pyridinaneN (5) ligand (Me (2)[15] pyridinaneN (5) = trans-2,13-dimethyl-3,6,9,12,18-pentaazabicyclo [12.3.1] octadeca-1 (18),14,1 6-triene), which belongs to the class of proven superoxide dismutase (SOD) mimetics. The X-ray crystal structures of 2-4 were determined. All complexes possess pentagonal-bipyramidal geometry with the pentadentate ligand in the equatorial plane and solvent molecules in the axial positions. The stopped-flow experiments in DMSO (0.06% of water) reveal that all four metal complexes catalyze the fast disproportionation of superoxide under the applied experimental conditions, and the catalytic rate constants are found to be (3.7 +/- 0.5) x 10 (6), (3.9 +/- 0.5) x 10 (6), (1.2 +/- 0.3) x 10 (7), and (5.3 +/- 0.8) x 10 (6) M (-1) s (-1) for 1-4, respectively. The cytochrome c McCord-Fridovich (McCF) assay in an aqueous solution at pH = 7.8 resulted in the IC (50) values (and corresponding kMcCF constants) for 3 and 4, 0.013 +/- 0.001 microM (1.9 +/- 0.2 x 10 (8) M (-1) s (-1)) and 0.024 +/- 0.001 microM (1.1 +/- 0.3 x 10 (8) M (-1) s (-1)), respectively. IC (50) values from a nitroblue tetrazolium assay are found to be 6.45 +/- 0.02 and 1.36 +/- 0.03 microM for 1 and 4, respectively. The data have been compared with those obtained by direct stopped-flow measurements and discussed in terms of the side reactions that occur under the conditions of indirect assays. |
2(0,0,0,2) |