TY - JOUR
T1 - Photochemical reactions of coenzyme PQQ (pyrroloquinolinequinone) and analogues with benzyl alcohol derivatives via photoinduced electron transfer
AU - Fukuzumi, Shunichi
AU - Itoh, Shinobu
AU - Komori, Takashi
AU - Suenobu, Tomoyoshi
AU - Ishida, Akito
AU - Fujitsuka, Mamoru
AU - Ito, Osamu
PY - 2000/9/6
Y1 - 2000/9/6
N2 - Photochemical redox reactions of the trimethyl ester of coenzyme PQQ (PQQTME) with benzyl alcohol derivatives (ArCH2OH), tetrahydrofuran, and 1,4-cyclohexadiene occur efficiently under visible light irradiation in MeCN to yield PQQTMEH2 (reduced PQQTME in the quinol form) and the corresponding dehydrogenated products (ArCHO, furan, and benzene) quantitatively. A similar photochemical oxidation of benzyl alcohols also occurs with phenanthrolinequinone derivatives (PTQ), benzoquinolinequinone derivatives (BQQ), and phenanthrenequinone (PQ). PQQTME and the analogues are essentially nonfluorescent in MeCN, and the photochemical reaction of the o-quinones is retarded significantly in the presence of molecular oxygen. Transient absorption spectra of the triplet excited states of the o-quinones were detected in laser flash photolysis of the MeCN solutions. From the decay of T-T spectra were determined the lifetimes of the triplet excited states of the o-quinones. The quenching rate constants of the triplet excited states by benzyl alcohols agree with the observed rate constants of the photochemical reduction of the o-quinones with the same substrates determined from the saturated dependence of quantum yields on the benzyl alcohol concentrations. Such an agreement confirms that the photochemical reaction proceeds via the triplet excited state of the quinones. Dependence of the observed rate constants k(obs) of the photochemical redox reaction on the one-electron oxidation potential E(o)(ox) of the substrates as well as the results of kinetic deuterium isotopic study indicates that the photochemical redox reactions between the o-quinones and the substrates proceed via photoinduced electron transfer from the substrate to the triplet excited state of the o-quinone, followed by proton and hydrogen atom transfer to yield the quinol and the corresponding oxidation products. The transient absorption spectra of the radical ion pair formed in the photoinduced electron transfer have been detected successfully in laser flash photolysis of the o-quinone-benzyl alcohol systems.
AB - Photochemical redox reactions of the trimethyl ester of coenzyme PQQ (PQQTME) with benzyl alcohol derivatives (ArCH2OH), tetrahydrofuran, and 1,4-cyclohexadiene occur efficiently under visible light irradiation in MeCN to yield PQQTMEH2 (reduced PQQTME in the quinol form) and the corresponding dehydrogenated products (ArCHO, furan, and benzene) quantitatively. A similar photochemical oxidation of benzyl alcohols also occurs with phenanthrolinequinone derivatives (PTQ), benzoquinolinequinone derivatives (BQQ), and phenanthrenequinone (PQ). PQQTME and the analogues are essentially nonfluorescent in MeCN, and the photochemical reaction of the o-quinones is retarded significantly in the presence of molecular oxygen. Transient absorption spectra of the triplet excited states of the o-quinones were detected in laser flash photolysis of the MeCN solutions. From the decay of T-T spectra were determined the lifetimes of the triplet excited states of the o-quinones. The quenching rate constants of the triplet excited states by benzyl alcohols agree with the observed rate constants of the photochemical reduction of the o-quinones with the same substrates determined from the saturated dependence of quantum yields on the benzyl alcohol concentrations. Such an agreement confirms that the photochemical reaction proceeds via the triplet excited state of the quinones. Dependence of the observed rate constants k(obs) of the photochemical redox reaction on the one-electron oxidation potential E(o)(ox) of the substrates as well as the results of kinetic deuterium isotopic study indicates that the photochemical redox reactions between the o-quinones and the substrates proceed via photoinduced electron transfer from the substrate to the triplet excited state of the o-quinone, followed by proton and hydrogen atom transfer to yield the quinol and the corresponding oxidation products. The transient absorption spectra of the radical ion pair formed in the photoinduced electron transfer have been detected successfully in laser flash photolysis of the o-quinone-benzyl alcohol systems.
UR - http://www.scopus.com/inward/record.url?scp=0033824823&partnerID=8YFLogxK
U2 - 10.1021/ja001351g
DO - 10.1021/ja001351g
M3 - Article
AN - SCOPUS:0033824823
SN - 0002-7863
VL - 122
SP - 8435
EP - 8443
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 35
ER -