Reactions of water soluble iron(II) and cobalt(II) porphyrins with nitric oxide. Implications for the reactivity of NO and biologically relevant metal centers

Abstract

The entropies and volumes of activation (ΔS‡_on and ΔV‡_on) for the fast reactions (k_on > 10⁹ dm³ mol^–1 s^–1) reaction of NO with the water soluble iron(II) porphyrin complexes Fe^II(TPPS) [TPPS = tetrakis(4-sulfonatophenyl)porphinato] and Fe^II(TMPS) [TMPS = tetrakis(sulfonatomesityl)porphinato] are small and positive indicating that these reactions are dominated by the diffusion processes as is the analogous formation of the cobalt(II) complex Co^II(TPPS)(NO).