NEW DNA-BINDING RUTHENIUM(II) COMPLEXES AS PHOTOREAGENTS FOR MONONUCLEOTIDES AND DNA

The spectroscopic properties of two photoprobes for DNA, Ru(phen)(2)(P HEHAT)(2+) and Ru(TAP)(2)(PHEHAT)(2+) (phen = 1,10-phenanthroline, TAP = 1,4,5,8-tetraazaphenanthrene, PHEHAT = 1,10-phenanthrolino [5,6-b]- 1,4,5,8,9,12-hexaazatriphenylene), were examined and compared with tho se of complexes containing either an extended planar ligand (DPPZ) or pi-acceptor ligands. The orbitals involved in the absorption and emiss ion processes for Ru(phen)(2)(PHEHAT)(2+) imply the PHEHAT ligand, whe reas the chromophore and luminophore for Ru(TAP)(2)(PHEHAT)(2+) are as sociated with the Ru(II) --> TAP MLCT transition. The two complexes ex hibit completely different behaviour in the presence of DNA. Whereas R u(phen)(2)(PHEHAT)(2+), which does not emit in water, luminesces upon intercalation between the DNA base pairs, the luminescence of Ru(TAP)( 2)(PHEHAT)(2+) is quenched by binding to DNA. Emission quenching is al so observed in the presence of GMP, with a quenching rate constant of 1.25 x 10(9) l mol(-1) s(-1). This strongly suggests the presence of a photoinduced electron transfer from the guanine residues of GMP or DN A to the excited complex and leads to the conclusion that this complex is a good DNA photoreagent. (C) 1998 John Wiley & Sons, Ltd.