Decomposition kinetics of peroxynitrite: influence of pH and buffer

Abstract

The decay of ONOOH near neutral pH has been examined as a function of isomerization to H⁺ and NO₃⁻, and decomposition to NO₂⁻ and O₂via O₂NOO⁻. We find that in phosphate buffer k_{isomerization} = 1.11 ± 0.01 s⁻¹ and k_{disproportionation} = (1.3 ± 0.1) × 10³ M⁻¹ s⁻¹ at 25 °C and I = 0.2 M. In the presence of 0.1 M tris(hydroxymethyl)aminomethane (Tris), the decay proceeds more rapidly: k_{disproportionation} = 9 × 10³ M⁻¹ s⁻¹. The measured first half-life of the absorbance of peroxynitrite correlates with [Tris]₀·([ONOO⁻]₀ + [ONOOH]₀)², where the subscript 0 indicates initial concentrations; if this function exceeds 6.3 × 10⁻¹² M³, then Tris significantly accelerates the decomposition of peroxynitrite.