A water-soluble porphyrin dimer (PD) containing eight positive charges, bridged by 4,4'-dicarboxy-2,2'-bipyridyl, has been synthesized. Taking meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (H₂TMPyP) as a reference compound, interaction of the water-soluble porphyrin dimer with DNA was investigated by using absorption, fluorescence, CD spectroscopy, and the apparent affinity binding constant (K_app) of PD binding to CT DNA was measured to be 1.2×10⁶ L•mol^－1 by a competition method with ethidium bromide (EB) (that of H₂TMPyP was 6.9×10⁶ L•mol^－1). The cleavage ability of PD to pBR322 plasmid DNA was studied by gel electrophoresis. The results suggest that the binding modes of PD and CT DNA involve in both of intercalation and outside binding.

Key words: porphyrin dimer, DNA, apparent affinity binding constant, photocleavage