Institut de Chimie Moléculaire de l'Université de Bourgogne, UMR CNRS 5260, 9, Avenue Alain Savary BP 47870, 21078 DIJON Cedex, France.
Phys Chem Chem Phys. 2011 Aug 7;13(29):13327-32. doi: 10.1039/c0cp02700f. Epub 2011 Jun 28.
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(+).
我们对 pH 值范围为 2.5 至 12.5 的更简单水介质中 ubiquinone Q(2)（UQ(2)）的还原进行了全面研究。短异戊二烯链 ubiquinones（UQ(2)）被整合到自组装单层中。在这些条件下，可以基于九元方形方案描述整体 2e(-)电化学反应。确定了系统的热力学常数。整体 2e(-)过程由第二个电子的吸收控制。通过拟合实验速率常数得到的基本电化学速率常数为 k(s4) = 1.5 s(-1)，用于 QH˙(+)(2)↔ QH(2)，k(s5) = 1.5 s(-1)，用于 QH˙↔ QH(-)，k(s6) = 1 s(-1)，用于 Q˙(-)↔ Q(2-)。随着 pH 值的增加，依次涉及三个电化学反应 QH˙(+)(2)↔ QH(2)、QH˙↔ QH(-)和 Q˙(-)↔ Q(2-)。在电子吸收之前或之后，可以发生质子化或不发生质子化，反应路径从低 pH 值到高 pH 值为：e(-)，H(+)e(-)，e(-)H(+)，H(+)e(-)H(+)，H(+)e(-)和 e(-)H(+)。
