Interaction of tetra-azaphenanthrene ruthenium complexes with DNA and oligonucloetides. A photophysical and photochemical investigation

The interaction of complexes Ru(bpy)(n)(TAP)(3-n)2+ (1a-1d for n = 0-3) with DNA has been investigated using photophysical methods (emission spectroscopy and laser flash photolysis), by studying the induction of single-strand breaks in plasmid DNA and the formation of adducts using 32P-labelled 27-mer oligonucleotides. Two classes of behaviour are found. Complexes 1a and 1b show quenched emission in the presence of calf thymus DNA and yield photoadducts with the 27-mer, whereas 1c and 1d show enhanced emission and do not form photoadducts. 1a and 1b are more efficient sensitizers for single-strand breaks than are 1c and 1d. It is proposed that the excited states of 1a and 1b, which are stronger oxidizing agents than those of 1c and 1d, are capable of oxidizing guanine. Direct evidence for electron transfer has been obtained from laser flash photolysis of Ru(TAP)32+ and dGMP, CT-DNA and polynucleotides.