Nickel(II) complexes of tetradentate ligands such as cyclam and salen
are catalysts for olefin epoxidation using PhIO and NaOCl, respectivel
y. In order to understand the lack of enantioselectivity observed with
chiral cyclam and salen complexes, studies of DNA and RNA oxidation w
ere carried out in which evidence for diffusible oxidants might be fou
nd. A variety of square-planar, tetradentate nickel(II) complexes were
observed to mediate guanine-specific modification in the presence of
KHSO5 or magnesium monoperphthalate. In particular, the cationic compl
ex, [(2,12-dimethyl-3,7,11,17-tetraazabicyclo heptadeca-1(17),2,11,13,
15-pentaenato)nickel](2+), [NiCR](2+), has been studied as a probe of
nucleic acid folding. The extent of guanine reaction depends upon the
exposure of N7, a good transition metal binding site, thus implicating
nickel-guanine binding during DNA oxidation. If this is the case, rel
ated systems should be able to confer enantioselectivity during the us
e of chiral nickel complexes and achiral substrates for oxidation. Mec
hanistic studies, including radical quenching and DNA enantioselectivi
ty, are described and their mechanistic implications discussed.