Mechanistic information on the reaction of cis- and trans-[RuCl2(DMSO)(4)] with d(T(2)GGT(2)) derived from MALDI-TOF and HPLC studies

Reactions of trans and cis isomers of the Ru-II complex [RuCl2(DMSO)(4)] with single-stranded hexanucleotide d(T(2)GGT(2)) were studied in aqueous solutions in the absence and presence of excess chloride by high performance liquid chromatography (HPLC) and matrix-assisted laser desorption/ionisation time of flight mass spectrometry (MALDI-TOF MS). Despite the different reactive species formed from the two isomers in aqueous solution, similar reaction products are obtained in their interaction with d(T(2)GGT(2)). Both [RuCl2(DMSO)(4)] isomers bind to the oligonucleotide in the bidentate mode to form thermodynamically stable bis-guanosine adducts, Ru(G-N7)(2), Significant differences were observed in the reaction rates, however the reaction with trans[RuCl2(DMSO)(4)] is ca. 5-10 times faster in comparison to that observed for the cis analogue. This difference is interpreted in terms of different rate-limiting steps for the trans and cis complexes, respectively. It is suggested that the rate of the reaction with the trans isomer is controlled by dissociation of a Cl- ligand from the initially formed trans, cis, cis-[RuCl2(DMSO)(2)(H2O)(2)]. In the contrast, release of a dimethyl sulfoxide molecule from the reactive species cis,fac-[RuCl2(DMSO)(3)(H2O)] is likely to be rate limiting for the cis analogue. Significant influence of electrostatic interactions on the reaction rate was observed for the trans isomer. Mechanistic interpretation of the observed reactivity trends based on data obtained from UV-Vis spectroscopy, HPLC and MALDI-TOF MS studies is presented and discussed within the paper