DNA binding and cleavage studies of novel Betti base substituted quaternary Cu(II) and Zn(II) phthalocyanines

Abstract

Betti base substituted zinc and copper phthalocyanines (ZnBBPc and CuBBPc) and their quaternized derivatives qZnBBPc and qCuBBPc were synthesized and characterized for the first time. The photophysical quantum yield (ΦF) and singlet oxygen quantum yield (ΦΔ) of ZnBBPc and qZnBBPc were measured using comparative and 1,3-diphenylisobenzofuran (DPBF) absorption titration methods respectively. The DNA binding activities of qZnBBPc and qCuBBPc against Calf-Thymus DNA (CT-DNA) were investigated using UV–visible absorption titrations, fluorescent displacement assays with classical intercalator ethidium bromide (EB) and minor groove binder Hoechst dye (HD), as well as by carrying out viscosity measurements in Tris-NaCl buffer (pH 7.4). The results indicated that qCuBBPc and qZnBBPc phthalocyanines showed strong affinities for CT-DNA through intercalation with binding constants (Kb) of the order of 105 M−1. The cleavage activities of compounds on supercoiled pBR322 plasmid DNA were determined by agarose gel electrophoresis in the presence and absence of light and additives. The compound qCuBBPc showed hydroxyl radical mediated oxidative cleavage, while the complex qZnBBPc exhibited singlet oxygen mediated photocleavage.