Kinetic-mechanistic studies of ruthenium macrocyclic complexes formation as potential donors and scavengers of nitric oxide and correlated species

In this paper, the mechanisms of reactions involving complexes with tetraazamacrocyclic (mac) ligands against nitrosyl ligands in an aqueous medium were explored, with emphasis on reactivity to nitric oxide (NO) and analog species, like nitrite ion (NO₂⁻). The reactions between [RuCl(OH₂)(mac)]²⁺ with NO and [RuCl(OH)(mac)]²⁺ with NO₂⁻ were performed in an aqueous solution within pH 1 or 7, and the rate constants (k) and the thermodynamic parameters (∆H^#, ∆S^#) of activation were determined. The reaction between NO and the complex with cyclen is faster than that with the complex with cyclam. However, the reaction of the cyclen complex with NO₂⁻ is slower than NO. This research provides detailed reaction kinetics and thermodynamic activation parameters for these interactions for the first time. In addition, the redox processes of coordinated NO⁻ and NO₂⁻ ligands to ruthenium were evaluated and the electrochemical release of NO from nitrosyl compounds upon electrochemical potential application. Our findings bring significant contributions in elucidating mechanisms related to NO capture both in vitro and in vivo.