Structural feature of calf thymus deoxyribonucleic acid–ruthenium(III) interaction in aqueous solution by difference Fourier transformed infrared spectroscopy

Here is the report on the interaction of ruthenium(III) species with DNA in aqueous solution at pH 7.42 by Fourier transformed infrared difference spectroscopy. Under the physiological pH and molar ratio [Ruthenium]/[DNA]=1/80-1/20 direct binding to guanine-N7, adenine-N7, and surprising binding to exocyclic thymine-O2 was found. At low metal concentration no significant shift of the absorption bands was observed, only nonspecific electrostatic binding of ruthenium(III) with negatively charged phosphate groups occurred. The increase of ruthenium(III) concentration caused DNA double helix destabilization and direct binding of the metal cation to guanine-N7 and thymine-O2. At higher ruthenium(III) concentrations denaturation of the DNA helix is evident with no apparent binding of ruthenium(III) to adenine and cytosine. Helix opening allows migration of ruthenium(III) ions from phosphate to available nucleobases (guanine and thymine). No alteration of the sugar phosphate geometry was observed thus confirming that DNA remains in B conformation.