Distance-dependent diffusion-controlled reaction of *NO and O2*- at chemical equilibrium with ONOO-.

Horacio Botti (1, 2) , Matías N Möller (1, 3, 4) , Daniel Steinmann (5) , Thomas Nauser (5) , Willem H Koppenol (5) , Ana Denicola (1, 3) , Rafael Radi (1, 6)

1 Center for free Radical and Biomedical Research
2 Institut Pasteur de Montevideo
3 Laboratorio de Fisicoquimica Biologica
4 Vanderbilt Institute of Chemical Biology
5 D-CHAB - Department of Chemistry and Applied Biosciences [ETH Zürich]
6 Departamento de Bioquimica

The fast reaction of (*)NO and O(2)(*-) to give ONOO(-) has been extensively studied at irreversible conditions, but the reasons for the wide variations in observed forward rate constants (3.8 ≤ k(f) ≤ 20 × 10(9) M(-1) s(-1)) remain unexplained. We characterized the diffusion-dependent aqueous (pH > 12) chemical equilibrium of the form (*)NO + O(2)(*-) = ONOO(-) with respect to its dependence on temperature, viscosity, and [ONOO(-)](eq) by determining [ONOO(-)](eq) and [(*)NO](eq). The equilibrium forward reaction rate constant (k(f)(eq)) has negative activation energy, in contrast to that found under irreversible conditions. In contradiction to the law of mass action, we demonstrate that the equilibrium constant depends on ONOO(-) concentration. Therefore, a wide range of k(f)(eq) values could be derived (7.5-21 × 10(9) M(-1) s(-1)). Of general interest, the variations in k(f) can thus be explained by its dependence on the distance between ONOO(-) particles (sites of generation of (*)NO and O(2)(*-)).

Domains: Chemical Sciences; Other

Horacio Botti, Matías N Möller, Daniel Steinmann, Thomas Nauser, Willem H Koppenol, et al.. Distance-dependent diffusion-controlled reaction of *NO and O2*- at chemical equilibrium with ONOO-.. Journal of Physical Chemistry B, 2010, 114 (49), pp.16584-93. ⟨10.1021/jp105606b⟩. ⟨pasteur-00685045⟩