title: pKaof ubiquinone, menaquinone, phylloquinone, plastoquinone, and rhodoquinone in aqueous solution.
abstract: Quinones can accept two electrons and two protons, and are involved in electron transfer and proton transfer reactions in photosynthetic reaction centers. To date, the pKaof these quinones in aqueous solution have not been reported. We calculated the pKaof the initial protonation (Q·-to QH·) and the second protonation (QH-to QH2) of 1,4-quinones using a quantum chemical approach. The calculated energy differences of the protonation reactions Q·-to QH·and QH-to QH2in the aqueous phase for nine 1,4-quinones were highly correlated with the experimentally measured pKa(Q·-/QH·) and pKa(QH-/QH2), respectively. In the present study, we report the pKa(Q·-/QH·) and pKa(QH-/QH2) of ubiquinone, menaquinone, phylloquinone, plastoquinone, and rhodoquinone in aqueous solution.
authors.affiliation: Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8654, Japan.
authors.forename: Ryo
authors.initials: R
authors.lastname: Hasegawa
authors.affiliation: Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8654, Japan.|Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo, 153-8904, Japan.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Saito
authors.affiliation: Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8654, Japan.
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Takaoka
authors.affiliation: Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8654, Japan. hiro@appchem.t.u-tokyo.ac.jp.|Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo, 153-8904, Japan. hiro@appchem.t.u-tokyo.ac.jp.
authors.forename: Hiroshi
authors.identifier: http://orcid.org/0000-0002-5849-8150
authors.initials: H
authors.lastname: Ishikita
mesh_terms: D005075:Biological Evolution; D006863:Hydrogen-Ion Concentration; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism; D010971:Plastoquinone / Q000737:chemistry / Q000378:metabolism*; D011522:Protons; D012996:Solutions; D013816:Thermodynamics; D014451:Ubiquinone / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism*; D010837:Vitamin K 1 / Q000737:chemistry / Q000378:metabolism*; D024482:Vitamin K 2 / Q000737:chemistry / Q000378:metabolism*
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins; D011522:Protons; D012996:Solutions; D024482:Vitamin K 2; D014451:Ubiquinone; D010837:Vitamin K 1; C003304:rhodoquinone; D010971:Plastoquinone
keywords: Bacterial photosynthetic reaction centers; Blastochloris viridis; Evolutionary transition; Green non-sulfur bacteria; Photosystem II; Rhodobacter sphaeroides