Ruthenium tetraammines as a model of nitric oxide donor compounds

The nitric oxide liberation from trans-[Ru(NH3)(4)(L)(NO)](3+) (where L = py, 4-pic, isn, nic, L-His, 4-Clpy, imN) after one-electron -chemical or electrochemical reduction was investigated through spectroscopic and electrochemical techniques, reaction-product analysis and quantum-mechanic calculations. These complexes can be formally viewed as a Ru-11(NO+) species and the reduction site is located on the NO ligand. The Edegrees for the trans-[Ru-II(NH3)(4)(L)(NO+)](3+)/trans[Ru-II(NH3)(4)(L)(NO)](2+) redox process ranges from 0.072 V vs. NHE (nic) to -0.118 V vs. NHE (imN). The specific rate constants for NO dissociation from trans-[Ru-II(NH3)(4)(L)(NO)](2+), evaluated through double-step chronoamperometry, range from 0.025 s(-1) (nic) to 0.160 s(-1) (ImN) at 25degreesC. The [(RuNO+)-N-II/ (RuNO0)-N-II] redox potential and the specific rate constant (kappa(-No)), key steps for designing nitrosyl complexes as NO-donor drug prototypes, proved to be controlled by a judicious choice of the ligand (L) trans to NO. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)