NO Generation from the Cross-Talks between Ene-diol Antioxidants and Nitrite at Metal Sites.

The one-electron reduction of nitrite (NO 2 - ) to nitric oxide (NO) and ene-diol oxidation are two important biochemical transformations. Employing mononuclear cobalt-nitrite complexes with Co III and Co II oxidation states, [( Bz 3 Tren )Co III (nitrite) 2 ](ClO 4 ) ( 1 ) and [( Bz 3 Tren )Co II (nitrite)](ClO 4 ) ( 2 ), this report illustrates NO release coupled to stepwise oxidation of ene-diol antioxidants such as l-ascorbic acid (AH 2 ) and catechol. Analysis of the AH 2 end-product reveals that the reaction with complex 1 affords dehydroascorbic acid. Intriguingly, a controlled oxidation of AH 2 with complex 2 results in a [Co II ]-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 [( Bz 3 Tren )M II (nitrite)](ClO 4 ) ( 2 , M = Co; 4 , M = Zn) provides mechanistic insights into the cross-talk between nitrite and ene-diols at the metal sites.