NO Generation from the Cross-Talks between Ene-diol Antioxidants and Nitrite at Metal Sites
Shourya Gupta, Swathy Vijayan, Jeffery A. Bertke, Subrata Kundu
Abstract
The one-electron reduction of nitrite (NO2–) to nitric oxide (NO) and ene-diol oxidation are two important biochemical transformations. Employing mononuclear cobalt-nitrite complexes with CoIII and CoII oxidation states, [(Bz3Tren)CoIII(nitrite)2](ClO4) (1) and [(Bz3Tren)CoII(nitrite)](ClO4) (2), this report illustrates NO release coupled to stepwise oxidation of ene-diol antioxidants such as l-ascorbic acid (AH2) and catechol. Analysis of the AH2 end-product reveals that the reaction with complex 1 affords dehydroascorbic acid. Intriguingly, a controlled oxidation of AH2 with complex 2 results in a [CoII]-bound ascorbyl radical-anion (8). Finally, NO release with the concomitant generation of metal-bound 3,5-di-tert-butyl-semiquinone radical anion from the reactions of 3,5-di-tert-butyl-catechol and [(Bz3Tren)MII(nitrite)](ClO4) (2, M = Co; 4, M = Zn) provides mechanistic insights into the cross-talk between nitrite and ene-diols at the metal sites.