Carboxylates as proton-accepting groups in concerted proton-electron transfers. Electrochemistry of the 2,5-dicarboxylate 1,4-hydrobenzoquinone/2,5-dicarboxy 1,4-benzoquinone couple.
Concerted proton and electron transfers (CPET) currently attract considerable theoretical and experimental attention, notably in view of their likely involvement in many enzymatic reactions. The role of carboxylate groups as proton-accepting sites in CPET reactions is explored by means of a cyclic voltammetric investigation of the 2,5-dicarboxy 1,4-benzoquinone/2,5-dicarboxylate 1,4-hydrobenzoquinone couple in a nonaqueous medium. The presence of carboxylate groups ortho to the phenol groups induces the removal of an electron to be coupled with the transfer of the phenolic proton to a carboxylate oxygen. The kinetics of the electrochemical reaction and the observation of a significant hydrogen/deuterium kinetic isotope effect unambiguously indicate that electron transfer and proton transfer are concerted, thus providing an additional demonstration of the role of carboxylate groups as proton-accepting sites in concerted proton-electron transfer reactions.
Costentin
Cyrille
C
Laboratoire d'Electrochimie Moléculaire, Unité Mixte de Recherche Université-CNRS 7591, Université de Paris 7-Denis Diderot, 2 place Jussieu, 75251 Paris Cedex 05, France.
Robert
Marc
M
Savéant
Jean-Michel
JM
D016227:Benzoquinones / Q000737:chemistry*; D002264:Carboxylic Acids / Q000737:chemistry*; D004563:Electrochemistry; D004583:Electrons; D007536:Isomerism; D007700:Kinetics; D015394:Molecular Structure; D011522:Protons
C522544:2,5-dicarboxy-1,4-benzoquinone; D016227:Benzoquinones; D002264:Carboxylic Acids; D011522:Protons