Photochemistry of Water‐soluble Quinones. Production of a Water‐derived Spin Adduct

Alegrı́a, Antonio E.; Ferrer, Amaris; Sepúlveda, Elsa

doi:10.1111/j.1751-1097.1997.tb03170.x

Cited by 62 publications

(72 citation statements)

References 27 publications

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“…Direct photolysis reactions of chromophoric dissolved organic matter (CDOM), such as pbenzoquinone 31 and humic substances, 4 are possible sources of OH radicals in river water, though further study is needed to confirm this.…”

Section: Oh Radical Photoformation Rates From Photo-fenton Reactions mentioning

confidence: 99%

Contribution of the Photo-Fenton Reaction to Hydroxyl Radical Formation Rates in River and Rain Water Samples

et al. 2007

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Section: Oh Radical Photoformation Rates From Photo-fenton Reactions mentioning

confidence: 99%

Contribution of the Photo-Fenton Reaction to Hydroxyl Radical Formation Rates in River and Rain Water Samples

et al. 2007

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“…Thus, NQ derivatives that are analogs or direct products of the naphthoate synthase enzyme appear to slow the growth of the wild-type cells. All three cyanobacterial strains ceased to grow shortly after addition of 5-OH-1,4-NQ, 2-CH 3 -5-OH-1,4-NQ, and 2,3-diCl-1,4-NQ, which are known herbicides (22)(23)(24).…”

Section: Isolation Of a High Light Tolerantmentioning

confidence: 99%

Recruitment of a Foreign Quinone into the A1 Site of Photosystem I

Johnson

Zybailov

Jones

et al. 2001

Journal of Biological Chemistry

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Substituted quinones are usually employed as cofactors in electron transport chains, as demonstrated in bacterial reaction centers (1, 2), and in the two photosystems of plants and cyanobacteria (3-5). These quinones comprise a relatively polar ring, which consists of either a benzoquinone (BQ) 1 or a naphthoquinone (NQ) "head group" and a non-polar isoprenoid "tail" of various chain lengths and degrees of saturation. Benzoquinones such as plastoquinone-9 (PQ-9) and ubiquinone-10 function either as fixed or exchangeable electron/proton carriers during photosynthetic and respiratory electron transport. In photosystem II (PS II), PQ-9 functions as a bound one-electron cofactor in the Q A site and as an exchangeable two-electron/ two-proton cofactor in the Q B site. The reduced PQH 2 -9 is displaced from the Q B site, diffuses laterally through the membrane, and becomes oxidized and deprotonated by the cytochrome b 6 f complex. Photosynthetic reaction centers (RCs) of purple bacteria use either ubiquinone-10 (e.g. Rhodobacter sphaeroides) in a similar double role or menaquinone-9 in the Q A site (e.g. Rhodosprillulum viridis). In photosystem I (PS I), phylloquinone (PhQ), a substituted 1,4-NQ with a 20-carbon, largely saturated phytyl tail, functions as a bound one-electron cofactor in the A 1 site. PS I contains two PhQ molecules/P700, but neither of the two quinones functions in a manner equivalent to Q B in the bacterial RC and PS II. Instead, the electron is transferred from the active quinone(s) to soluble ferredoxin via a chain of three bound iron-sulfur centers. Quinones are therefore extremely versatile; they can function as the interface between electron transfer involving organic cofactors and electron transfer involving iron-sulfur clusters (as in PS I), or between pure electron transfer and coupled electron/proton transfer involving a second organic cofactor (as in PS II). Each quinone displays equilibrium binding and redox properties that can be very different for each site of interaction (6), and these properties are conferred largely by the protein environment.To understand the structural determinants that allow quinones to function with a low redox potential in the A 1 site of PS I, we embarked on a project aimed at biological replacement of

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“…[38] This is in contrast to data which indicate that in this system 1,4-benzosemiquinonetype radicals must be minor contributors to photohydroxylation (< 10 %) compared with a non-radical pathway. [37] Based on spin-trapping experiments, it has been suggested [39,44,45] that the first step is an H-abstraction from water [reaction (4)}, that is, that the reaction is analogous to reaction (1).…”

mentioning

confidence: 99%

Photohydroxylation of 1,4‐Benzoquinone in Aqueous Solution Revisited

Sonntag

Mvula

Hildenbrand

et al. 2004

Chemistry A European J

129

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In water, photolysis of 1,4-benzoquinone, Q gives rise to equal amounts of 2-hydroxy-1,4-benzoquinone HOQ and hydroquinone QH(2) which are formed with a quantum yield of Phi=0.42, independent of pH and Q concentration. By contrast, the rate of decay of the triplet (lambda(max)=282 and approximately 410 nm) which is the precursor of these products increases nonlinearly (k=(2-->3.8) x 10(6) s(-1)) with increasing Q concentration ((0.2-->10) mM). The free-radical yield detected by laser flash photolysis after the decay of the triplet also increases with increasing Q concentration but follows a different functional form. These observations are explained by a rapid equilibrium of a monomeric triplet Q* and an exciplex Q(2)* (K=5500+/-1000 M(-1)). While Q* adds water and subsequent enolizes into 1,2,4-trihydroxybenzene Ph(OH)(3), Q(2)* decays by electron transfer and water addition yielding benzosemiquinone (.)QH and (.)OH adduct radicals (.)QOH. The latter enolizes to the 2-hydroxy-1,4-semiquinone radical (.)Q(OH)H within the time scale of the triplet decay and is subsequently rapidly (microsecond time scale) oxidized by Q to HOQ with the concomitant formation of (.)QH. On the post-millisecond time scale, that is, when (.)QH has decayed, Ph(OH)(3) is oxidized by Q yielding HOQ and QH(2) as followed by laser flash photolysis with diode array detection. The rate of this pH- and Q concentration-dependent reaction was independently determined by stopped-flow. This shows that there are two pathways to photohydroxylation; a free-radical pathway at high and a non-radical one at low Q concentration. In agreement with this, the yield of Ph(OH)(3) is most pronounced at low Q concentration. In the presence of phosphate buffer, Q* reacts with H(2)PO(4) (-) giving rise to an adduct which is subsequently oxidized by Q to 2-phosphato-1,4-benzoquinone QP. The current view that (.)OH is an intermediate in the photohydroxylation of Q has been overturned. This view had been based on the observation of the (.)OH adduct of DMPO when Q is photolyzed in the presence of this spin trap. It is now shown that Q*/Q(2)* oxidizes DMPO (k approximately 1 x 10(8) M(-1) s(-1)) to its radical cation which subsequently reacts with water. Q*/Q(2)* react with alcohols by H abstraction (rates in units of M(-1) s(-1)): methanol (4.2 x 10(7)), ethanol (6.7 x 10(7)), 2-propanol (13 x 10(7)) and tertiary butyl alcohol ( approximately 0.2 x 10(7)). DMSO (2.7 x 10(9)) and O(2) ( approximately 2 x 10(9)) act as physical quenchers.

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Photochemistry of Water‐soluble Quinones. Production of a Water‐derived Spin Adduct

Cited by 62 publications

References 27 publications

Contribution of the Photo-Fenton Reaction to Hydroxyl Radical Formation Rates in River and Rain Water Samples

Contribution of the Photo-Fenton Reaction to Hydroxyl Radical Formation Rates in River and Rain Water Samples

Recruitment of a Foreign Quinone into the A1 Site of Photosystem I

Photohydroxylation of 1,4‐Benzoquinone in Aqueous Solution Revisited

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