How does the pH influences the Ru‐NO coordination compounds?

The pH influence has important role in the bioavailability of coordination compounds. fac ‐[Ru(NO)Cl 2 (κ 3 N 4 ,N 8 ,N 11 [1‐carboxypropyl]cyclam)] + , 1 , and the species found at different pHs, 2 ‐ 4 , were investigated. One series of computational methodologies has been used to investigate these compounds. One special highlight is to interacting quantum atom s method, where the total interaction energy, E int AB , between two atoms has been used as base to estimate the chemical bonds strength. The deprotonation of ‐CO 2 H, 1 ➔ 2 (pK a = 3.3), creates a hydrogen bond in the complex 2 , N( 3 )‐H⋯ ·OCO − , with a more favorable E int AB than the presents in 1 , N( 3 )‐H⋯ ·OCOH. There are no changes in E int AB in Ru ‐ NO bond. The second deprotonation occurs in the N(2) atom of the cyclam group, 2 ➔ 3 (pK a = 8.0). It promotes an increase in the covalent character of Ru‐N( 2 ). In contrast, there is no changes in Ru‐N( 5 )O bond. For higher pHs, there is a 3 ➔ 4 equilibrium (pK a = 11.5) and the conversion of Ru‐N( 5 )O for Ru‐N( 5 )O 2 . The Ru‐N( 5 ) of 4 shows a larger ionic character than 3 . Thus, Ru‐NO in 1 ‐ 4 has worthy stability about a large pH range, showing potential application as NO scavengers.