Nitric oxide and nitroxyl formation in the reduction of trans-tetraamminenitrosyltriethylphosphiteruthenium(II) ion

Nitroxyl as a ligand in ruthenium tetraammine systems: a density functional theory study

The properties of the free nitroxyl molecule and the nitroxyl ligand in Ru(ii) tetraammines (trans-[Ru(NH₃)₄(nitroxyl)ⁿ(L)]²⁺ⁿ (n = nitroxyl charge; L = NH₃, py, P(OEt)₃, H₂O, Cl⁻ and Br⁻)) were studied using density functional theory.

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

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.

Unexpected NO transfer reaction between trans-[Ru(II)(NO+)(NH3)4(L)]3+ and Fe(III) species: observation of a heterobimetallic NO-bridged intermediate

The reaction between trans-[Ru(II)(NO(+))(NH3)4(L)](3+), L = ImN, IsN, Nic, P(OMe)3, P(OEt)3, and P(OH)(OEt)2, and the Fe(III) species [Fe(III)(TPPS)], metmyoglobin, and hemoglobin was monitored by UV-vis, EPR, and electrochemical techniques (DPV, CV). No reaction was observed when L = ImN, IsN, Nic, and P(OH)(OEt)2. However, when L = P(OMe)3 and P(OEt)3, the reaction was quantitative and the products were trans-[Ru(III)(H2O)(NH3)4(P(OR)3)](3+) and [Fe(II)(NO(+))] species. Reaction kinetics data and DFT calculations suggest a two-step reaction mechanism with the initial formation of a bridged [Ru-(μNO)-Fe] intermediate, which was confirmed through electrochemical techniques (E(0)' = -0.47 V vs NHE). The calculated specific rate constant values for the reaction were in the ranges k1 = 1.1 to 7.7 L mol(-1) s(-1) and k2 = 2.4 × 10(-3) to 11.4 × 10(-3) s(-1) for L = P(OMe)3 and P(OEt)3. The oxidation of the ruthenium center (Ru(II) to Ru(III)) containing the nitrosonium ligand suggests that NO can act as an electron transfer bridge between the two metal centers.