DNA-binding properties and photocleavage activity of cationic water-soluble chlorophyll derivatives

Three cationic water-soluble chlorin e₆ derivatives, that is, 6a-,γb-,7c-tris(2-trimethylammonioethyl)chlorin e₆ (1), 6a-,γb-,7c-tris(3-methylpyridi-niummethyl)chlorin e₆ (2), and 6a-,γb-, 7c-tris(2-trimethylammonioethyl)-2-(3trimethylammonioprop-1-enyl)chlorin e ₆ (3), have been designed and synthesized to allow the study of their DNA-binding and -photocleavage activities. The DNA-unwinding assay, measurements of melting temperatures of double-stranded DNA, and the induced CD and visible absorption spectra have revealed that 1 and 3 are intercalated into the base pairs of the double-helical DNA, while 2 is bound to outside the minor groove of the double-helical DNA. The cationic water-soluble chlor-in e ₆ derivatives effectively cleave the double-helical DNA under photoirradiation and the DNA-photocleavage activity increases in the order 3 > 1 > 2. The DNA-binding and -photocleavage characteristics of the three cationic water-soluble chlorin e₆ derivatives are influenced by aspects of their molecular structure, such as the kind, number, and position of the cationic substituents.