Mechanistic information on the redox cycling of nickel(II/III) complexes in the presence of sulfur oxides and oxygen. Correlation with DNA damage experiments

The reactions of the water-soluble complexes [NiCR](2+) (where CR = 2,12-di methyl-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),2,11,13,15-pentaene ) and [NiKGH-CONH2](+) (where KGH-CONH2 = lysylglycylhistidinecarboxamide) with sulfite/O-2 and peroxymonosulfate have been investigated using spectro photometric and rapid-scan techniques. In most cases, the spectral changes suggest the formation of an intermediate Ni(III) species, followed by decom position reactions which involve a back-reaction to Ni(II). Only in the cas e of the [NiCR](2+)-S(IV)-O-2 system is the formed Ni(III) species stable i n solution. When sulfite and oxygen an used to oxidize Ni(II) to Ni(III), t he reaction is oxygen dependent and an induction period could be observed, whereas the use of the strong oxidizing agent peroxymonosulfate resulted in no induction period and no oxygen dependence-In addition, the oxidation of Ni(II) to Ni(III) was faster if peroxymonosulfate was used instead of sulf ite/O-2. The [NiKGH-CONH2](+) complex reacts much faster with sulfite/O-2 a nd peroxymonosulfate than the [NiCR](2+) does. Rate constants for the oxida tion process and possible reaction mechanisms, based on available literatur e data, that can account for the observed kinetic observations in a qualita tive way are presented, and the results are correlated with previously obta ined data on DNA modification using these systems.