Abstract: S-Nitrosodipeptides are generally believed to be good NO donors, and many NO-related biological functions have been directly associated with S-nitrosodipeptides, especially in the processes of NO-storage, transport and delivery. In this work, the heterolytic and homolytic S—NO bond dissociation energies of seven S-nitrosodipeptides were evaluated via titration calorimetry and relative thermodynamic cycles. The energetic scales of the heterolytic and homolytic S—NO bond dissociation energies of these RSNOs covered the ranges 234.5—246.2 and 101.6—122.1 kJ/mol, respectively, which indicated that the studied S-nitrosodipeptides were much easier to release a NO radical(NO^·) rather than a NO cation(NO⁺). The estimation of the heterolytic and homolytic(S—NO)^-· bond dissociation energies of the S-nitrosodipeptides radical anions gave the energetic ranges of 19.2—35.5 and 4.2—22.6 kJ/mol for the(S—NO)^-· bond homolysis and heterolysis, respectively, which meant that S-nitrosodipeptides radical anions were unstable at room temperature and favored to releasing a NO anion(NO^-) by heterolysis cleavage.

Key words: S-Nitroso-N-acetyl-D,L-penicillamine, S—NO bond energy, Radical anions, Titration calorimetry