Probing the interaction between DNA and cells transfection polymers with luminescent Ru(II) complexes

The luminescence properties of RuII complexes [Ru(TAP)2(phen)]Cl2 (1), [Ru(TAP)2(TPAC)]Cl2 (2) and [Ru(phen)2(TPAC)]Cl2 (3) (TAP = 1,4,5,8-tetraazaphenanthrene and TPAC = tetrapyrido-acridine) were used for probing the interactions of cell transfection (co)polymers, such as poly[2-dimethylaminoethyl-methacrylate] (PDMAEMA) and poly[2-dimethylaminoethylmethacrylate]-b-poly[(ethylene glycol-a-methylether-?-methacrylate] (P(DMAEMA-b-MAPEG)), with different polynucleotides (poly[(dA-dT)]2 and poly[(dG-dC)]2) and nucleic acids (calf thymus DNA and pBR322 plasmid DNA). It turned out that 1 was not a useful probe because its affinity constant for DNA was too weak. Moreover, 3 was also excluded because DNA-Ru complex aggregates complicated the interpretation of the data. 2 was the only candidate that could be used as a luminescent probe of 'DNA?polymer' self-assemblies that would penetrate cell membranes. Different (co)polymer/polynucleotide ratios were tested with complex 2 by luminescence measurements. The results showed that 2 is an interesting probe, which is very sensitive to changes in the polynucleotide double helix structure that are induced by interactions with the synthetic (co)polymer. Moreover, complex 2 has a mode of action of emission that is different from that of the classically used ethidium bromide, i.e. an increase in emission when certain 'polymer/DNA' ratios are reached during the titration of DNA with the polymer.