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Redox potentials of ubiquinone, menaquinone, phylloquinone, and plastoquinone in aqueous solution
Shinnosuke Kishi1, Keisuke Saito1,2, Yuki Kato3
1Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8654, Japan.
Abstract:
Quinones serve as redox active cofactors in bacterial photosynthetic reaction centers: photosystem I, photosystem II, cytochrome bc 1, and cytochrome b 6 f. In particular, ubiquinone is ubiquitous in animals and most bacteria and plays a key role in several cellular processes, e.g., mitochondrial electron transport. Their experimentally measured redox potential values for one-electron reduction E m(Q/Q·-) were already reported in dimethylformamide (DMF) versus saturated calomel electrode but not in water versus normal hydrogen electrode (NHE). We calculated E m(Q/Q·-) of 1,4-quinones using a quantum chemical approach. The calculated energy differences of reduction of Q to Q·- in DMF and water for 1,4-quinone derivatives correlated highly with the experimentally measured E m(Q/Q·-) in DMF and water, respectively. E m(Q/Q·-) were calculated to be -163 mV for ubiquinone, -260 mV for menaquinone and phylloquinone, and -154 mV for plastoquinone in water versus NHE.
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