Reactivity of [ RuIII(edta)(H2O)]– with nucleic bases, nucleosides and DNA (calf-thymus) in aqueous solution (etda = ethylenediamine-N,N,N′,N′-tetraacetate)

Abstract

Reactions of [Ru^III(edta)(H₂O)]^–(edta = ethylenediamine-N,N,N′,N′-tetraacetate) with L′(L′= adenine, adenosine, cytosine, cytidine or thymine) and calf-thymus DNA were studied by spectrophotometric, electrochemical and kinetic methods. Spectral features of the substituted product [Ru^III(edta)L′]^– complexes were characterised by a strong ligand-to-metal charge transfer (l.m.c.t.) band in the UV region (293–309 nm). The E_½ values for the Ru^III–Ru^II couple for [Ru^III(edta)L′]^– are in the range –0.28 to –0.15 V (vs. saturated calomel electrode). Equilibration kinetics of complexation of [Ru^III(edta)(H₂O)]^– with L′ have been investigated using stopped-flow methods at 25 °C and pH 5.2. Equilibrium constants determined kinetically are in good agreement with those obtained spectrophotometrically. The reactivity of L′ towards aqua-substitution of [Ru^III(edta)(H₂O)]^– complex follows the sequence adenine > adenosine > cytosine > cytidine. On the basis of spectrophotometric, electrochemical and kinetic data and comparing the reactivity of [Ru^III(edta)(H₂O)]^– with DNA bases and DNA (calf-thymus) itself it is proposed that the interaction of [Ru^III(edta)(H₂O)]^– with DNA takes place through the adenine base unit in a kinetically preferred pathway.