Characterisation of bifunctional ruthenium(II) complexes, potential DNA photo-probes. Presence of folded and unfolded conformers

Novel bifunctional ruthenium(II) complexes, [Ru(TAP)(2)(POQ-Nmet)](2+) and [Ru(BPY)(2)(POQ-Nmet)](2+) (1a, 2a), containing a metallic and an organic m oiety, have been prepared as photoprobes and photoreagents of DNA (TAP = 1, 4,5,8-tetraazaphenanthrene, POQ-Nmet = 5-[6-(7-chloroquinolin-4-yl)-3-thia- 6-azaheptanamido]-1,10-phenanthroline). The ES mass spectrometry and H-1 NM R data in organic solvents indicate that the quinoline moiety exists in bot h the protonated and non-protonated form. Moreover, the comparison of the N MR data with those of the corresponding monofunctional complexes (without q uinoline) evidences that [Ru(TAP)(2)(POQ-Nmet)](2+) and [Ru(BPY)(2)(POQ-Nme t)](2+) are unfolded when the quinoline unit is protonated whereas deproton ation permits folding of the molecule. In the folded state the spatial prox imity of the electron donor (the organic moiety) and electron acceptor (the metallic moiety) in [Ru(TAP)(2)(POQ-Nmet)](2+) favours intramolecular phot o-induced electron transfer, which has been shown in a previous study to be responsible for the very low luminescence of 1a in non-protonating solutio ns. The restoration of the luminescence by protonation of the quinoline moi ety as observed previously is in agreement with the unfolding of the molecu le demonstrated in this work. The existence of such folding-unfolding proce sses related to protonation is crucial for studies of 1a with DNA.