Synthesis, characterization and DNA binding study of Co(III) polypyridyl mixed-ligand complexes

Two complexes [Co(phen)(2)TATP](3+) and [Co(bipy)(2)TATP](3+), where TATP is the planar ligand 1,4,8,9-tetra-aza-triphenylene, were synthesized and characterized. The binding of Co(III) polypyridyl mixed-ligand complexes to calf thymus DNA was investigated using absorption spectroscopy, fluorescence spectroscopy, viscosity measurement, and DNA cleavage assay. The absorption spectroscopic studies showed that the two new complexes [Co(phen)(2)TATP](3+) and [Co(bipy)(2)TATP](3+) exihibited apparently higher intercalating efficiency to DNA base pairs than [Co(phen)(3)](3+) and [Co(bipy)(3)](3+). The fluorescence of DNA helix was quenched by Co(III) complexes very strongly. From the viscosity experiment, we inferred that the binding of [Co(phen)(3)](3+) to DNA may be not by classical intercalation. When irradiated at 302 nm, [Co(phen)(2)TATP](3+) induced single-strand scissions and [Co(bipy)(2)TATP](3+) induced double-strand scissions in supercoiled DNA. (C) 1998 Elsevier Science Ltd. All rights reserved.