Proton-coupled electron transfer reactions at a heme-propionate in an iron-protoporphyrin-IX model compound.

ABSTRACT: A heme model system has been developed in which the heme-propionate is the only proton donating/accepting site, using protoporphyrin IX-monomethyl esters (PPIX(MME)) and N-methylimidazole (MeIm). Proton-coupled electron transfer (PCET) reactions of these model compounds have been examined in acetonitrile solvent. (PPIX(MME))Fe(III)(MeIm)(2)-propionate (Fe(III)~CO(2)) is readily reduced by the ascorbate derivative 5,6-isopropylidine ascorbate to give (PPIX(MME))Fe(II)(MeIm)(2)-propionic acid (Fe(II)~CO(2)H). An excess of the hydroxylamine TEMPOH or of hydroquinone similarly reduces Fe(III)~CO(2), and TEMPO and benzoquinone oxidize Fe(II)~CO(2)H to return to Fe(III)~CO(2). The measured equilibrium constants, and the determined pK(a) and E(1/2) values, indicate that Fe(II)~CO(2)H has an effec

SUBMITTER: Warren JJ 

PROVIDER: S-EPMC3113656 | biostudies-literature | 2011 Jun

REPOSITORIES: biostudies-literature