Inorganic Chemistry, Vol.39, No.26, 5976-5984, 2000
Characterization of the Ni(III) intermediate in the reaction of (1,4,8,11-tetraazacyclotetradecane)nickel(II) perchlorate with KHSO5: Implications to the mechanism of oxidative DNA modification
We report the detection and characterization of the Ni(III) intermediates generated by reaction of (1,4,8,11-tetraazacyclotetradecane)nickel(II) perchlorate with KHSO5. Four Ni(III) intermediates can be trapped or detected through variation in Cl- or KHSO5 concentrations. Upon oxidation of [Ni(cyclam)](2+) by 2.5 equiv of KHSO5, deprotonation of the cyclam ligand generates two red Ni(III) species with lambda (max) = 530 nm and g(perpendicular to) = 2.20 and g(parallel to) = 2.02 or g(perpendicular to) = 2.16 and g(parallel to) = 2.01 for the axial 4-coordinate or 6-coordinate dichloride species, respectively. These forms decay to Ni(II) products via complex ligand oxidation mechanisms. The Ni(III) dichloride species can be reprotonated and subsequently binds to DNA via an outer-sphere interaction as evidenced by the inverted sign of the CD signal near 400 nm. Cumulatively, the results indicate that the Ni(III) center is coordinately saturated under excess chloride conditions but is still able to interact with DNA substrates. This suggests alternative mechanistic pathways for DNA modification by reaction of [Ni(cyclam)](2+) with KHSO5 and possibly other Ni(II) complexes as well.