Reaction of ruthenium nitrosyl complexes with superoxide

In Situ FT-IR Spectroelectrochemistry Reveals Mechanistic Insights into Nitric Oxide Release from Ruthenium(II) Nitrosyl Complexes

Ruthenium(II) tetraamine nitrosyl complexes with N-heterocyclic ligands are known for their potential as nitric oxide (NO•) donors, capable of releasing NO• through either direct photodissociation or one-electron reduction of the Ru(II)NO+ center. This study delivers a novel insight into the one-electron reduction mechanism for the model complex trans-[RuII(NO)(NH3)4(py)]3+ (RuNOpy, py = pyridine) in phosphate buffer solution (pH 7.4). In situ FT-IR spectroelectrochemistry reveals that the pyridine ligand is readily released upon one-electron reduction of the nitrosyl complex, a finding supported by nuclear magnetic resonance spectroscopy (1H NMR) and electrochemistry coupled to mass spectrometry (EC-MS), which detect free pyridine in solution. However, direct evidence of NO• release from RuNOpy as the primary step following reduction was not observed. Interestingly, FT-IR results indicate that the isomers of the nitrosyl complex, cis-[Ru(NO)(NH3)4(OH)]+ and trans-[Ru(NO)(NH3)4(OH)]+, are formed following reduction and pyridine labilization, initiating an outer-sphere electron transfer process that triggers a chain electron transfer reaction. Finally, nitric oxide is liberated as an end product, arising from the reduction of the hydroxyl isomer complexes cis-[Ru(NO)(NH3)4(OH)]2+ and trans-[Ru(NO)(NH3)4(OH)]2+. This study provides new insights into the reduction mechanism and transformation pathways of ruthenium nitrosyl complexes, contributing to our understanding of their potential as NO• donors.

Nitrosylruthenium Complexes as Polymerization Catalysts for Acrylonitrile in DMF

Nitrosylruthenium complexes bearing two 2,2'-bipyridine (bpy) or 2-pyridinecarboxylate (pyc) ligands, [Ru(NO)X(bpy)₂ ]³⁺ (X=CH₃ CN, CH₂ =CHCN, H₂ O, Cl, ONO₂ ) and [Ru(NO)(OH₂ )(pyc)₂ ]⁺ , were used as catalysts for the polymerization of acrylonitrile in N,N-dimethylformamide (DMF) under air without initiators to obtain polyacrylonitrile (PAN) with a high molecular weight and a narrow molecular weight distribution.

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.

Nitric oxide releasing-dendrimers: an overview

Platforms able to storage, release or scavenge NO in a controlled and specific manner is interesting for biological applications. Among the possible matrices for these purposes, dendrimers are excellent candidates for that. These molecules have been used as drug delivery systems and exhibit interesting properties, like the possibility to perform chemical modifications on dendrimers surface, the capacity of storage high concentrations of compounds of interest in the same molecule and the ability to improve the solubility and the biocompatibility of the compounds bonded to it. This review emphasizes the recent progress in the development and in the biological applications of different NO-releasing dendrimers and the nitric oxide release pathways in these compounds.