How the Acidic Milieu Interferes in the Capability of Ruthenium Nitrosyl Complexes to Release Nitric Oxide?
The nitric oxide (NO) molecule is related to a large number of biological routes. Thus, there is an increased interest in improving the understanding of the NO release mechanisms. One of the traditional NO release ways involves, for example: i) [Ru(NO)(NH3)5]3+ + e– → [Ru(NO)(NH3)5]2+; and ii) [Ru(NO)(NH3)5]2+ + H2O → [Ru(H2O)(NH3)5]2+ + NO, chemical reactions. Another possibility concerns to the light irradiation: iii) [Ru(NO)(NH3)5]3+ + H2O + hν → [Ru(H2O)(NH3)5]3+ + NO, aided by the Ru(dπ) → π*(NO) electronic transition, which decreases the π back–donation process in the Ru–NO chemical bond. The influence of the acid environment in which these chemical reactions typically occur experimentally has been explored in: iv) [Ru(NO)(NH3)5]2+ + H3O+ → [Ru(HNO)(NH3)5]3+ + H2O; and v) [Ru(HNO)(NH3)5]3+ + H2O → [Ru(H2O)(NH3)5]3+ + HNO, reactions. The reaction v), supported by eight explicit water molecules, was the most propitious to occur. The HNO charge obtained from atomic polar tensor scheme is close to zero. The Quantum Theory of Atoms in Molecules and Non–Covalent Interactions methods unravel that the HNO leaving group interacts with two water molecules through partially covalent or ionic chemical bonds. The HNO→NO conversion after the release from ruthenium molecules is thermodynamically feasible. The electronic spectrum of the structure [Ru(HNO)(NH3)5]3+ has, unlike the [Ru(NO)(NH3)5]3+ molecule, the Ru(dπ) → π*(NO) transition with an appropriate absorbance. Therefore, the proton increases the capability of ruthenium complexes to release nitric oxide after chemical reduction reaction or of the light supported chemical reaction.