Reaction of ruthenium(II) complexes with 2,2-diphenyl-1-picrylhydrazyl (DPPH•) and hydroxyl radicals

Abstract

The reaction of the complexes trans-[RuII(NO+)(NH3)4L] and [RuII(NO+)HEDTA] with 2,2-diphenyl-1-picrylhydrazyl (DPPH•) and hydroxyl (OH•) radicals has been investigated at 25.0 ± 0.1 °C using spectroscopic (UV-vis and electron paramagnetic resonance) and electrochemical techniques (differential pulse voltammetry and cyclic voltammetry). The redox potential of RuIII/RuII for the ruthenium nitrosyl complexes was determined and is in the range of +2.2 V (L = HEDTA) to +2.6 V (L = isn) versus the normal hydrogen electrode . The trans-[RuII(NO+)(NH3)4L]3+ and [RuII(NO+)HEDTA] complexes do not react with the DPPH• radical in aqueous solution at pH = 3.0. However, the corresponding aquo species, trans-[RuII(H2O)(NH3)4L]2+ and [RuII(H2O)HEDTA]+, respectively, react quantitatively, resulting in metal center oxidation. The trans-[RuII(NO+)(NH3)4L]3+ and [RuII(NO+)HEDTA] complexes react with OH• through a complicated pathway that leads to metal center oxidation followed by a series of secondary reactions. In addition to acting as NO donors, after their reduction, these ruthenium(II) nitrosyl complexes exhibit, through their generated aquo species, a radical scavenging ability, which is important for better understanding the already proven biological activity of these ruthenium nitrosyls in vivo.