Copper inverse-9-metallacrown-3 compounds interacting with DNA

Interaction of phenyl 2-pyridyl ketoxime (PhPyCNO)/X⁻“blends” (X⁻ = OH⁻, Cl⁻, ClO₄⁻, 2,4-D) (2,4-DH = 2,4-dichlorophenoxyacetic acid) with copper perchlorate has yielded trinuclear clusters that have been characterized as inverse-9-metallacrown-3, accommodating one or two anions. The structure of the complex [Cu₃(PhPyCNO)₃(μ₃-OH)(2,4-D)₂]·1.25CH₃OH·0.25CH₃CN (1) has been determined by single-crystal X-ray crystallography. Spectroscopic studies of the interaction of copper inverse {(OH)[9-MC_CuN(PhPyCNO)-3]} metallacrowns with DNA showed that these compounds bind to dsDNA by intercalative mode with an additional covalent {(OH)[9-MC_Cu(PhPyCNO)-3]}–DNA interaction leading to hydrolytic cleavage of DNA that may be assigned to the presence of the hydroxyl group in the inverse metallacrown ring. The binding strength of [Cu₃(PhPyCNO)₃(μ₃-OH)(2,4-D)₂] (1) complex for CT-DNA was determined to be 0.56 × 10⁵ M⁻¹. All the complexes exhibited the ability to displace the DNA-bound EthBr. DNA electrophoretic mobility experiments showed that all complexes, at low cluster concentration, are capable of binding to pDNA and linear DNA. At higher cluster concentration and in the absence of any reducing agent they showed marked chemical nuclease activity.