REACTIVITY OF [RU-III(EDTA)(H2O)](-) WITH NUCLEIC BASES, NUCLEOSIDES AND DNA (CALF-THYMUS) IN AQUEOUS-SOLUTION (ETDA=ETHYLENEDIAMINE-N,N,N',N'-TETRAACETATE)

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(1/2) 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 degrees 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.