title: Proton coupled electron transfer of ubiquinone Q2 incorporated in a self-assembled monolayer.
abstract: We present a complete study of the reduction of ubiquinone Q(2) (UQ(2)) in simpler aqueous medium, over a pH range of 2.5 to 12.5. The short isoprenic chain ubiquinones (UQ(2)) were incorporated in a self-assembled monolayer. Under these conditions, the global 2e(-) electrochemical reaction can be described on the basis of a nine-member square scheme. The thermodynamic constants of the system were determined. The global 2e(-) process is controlled by the uptake of the second electron. The elementary electrochemical rate constants obtained by fitting of the experimental rate constant were k(s4) = 1.5 s(-1) for QH˙(+)(2)↔ QH(2), k(s5) = 1.5 s(-1) for QH˙↔ QH(-) and k(s6) = 1 s(-1) for Q˙(-)↔ Q(2-). The three electrochemical reactions QH˙(+)(2)↔ QH(2), QH˙↔ QH(-) and Q˙(-)↔ Q(2-) are successively involved when increasing the pH. Protonations can occur or not, before or after the electron uptake and the reaction paths are, from low to high pH: e(-), H(+)e(-), e(-)H(+), H(+)e(-)H(+), H(+)e(-) and e(-)H(+).
authors.affiliation: Institut de Chimie Moléculaire de l'Université de Bourgogne, UMR CNRS 5260, 9, Avenue Alain Savary BP 47870, 21078 DIJON Cedex, France.
authors.forename: Celia
authors.initials: C
authors.lastname: Lemmer
authors.forename: Marcel
authors.initials: M
authors.lastname: Bouvet
authors.forename: Rita
authors.initials: R
authors.lastname: Meunier-Prest
mesh_terms: D004563:Electrochemistry; D004579:Electron Transport; D006046:Gold / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D010084:Oxidation-Reduction; D011522:Protons; D013499:Surface Properties; D013816:Thermodynamics; D014451:Ubiquinone / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D011522:Protons; D014867:Water; D014451:Ubiquinone; D006046:Gold; C025204:Ubiquinone Q2