Charge transfer and reactivity of n.pi.* and .pi..pi.* organic triplets, including anthraquinonesulfonates, in interactions with inorganic anions: a comparative study based on classical Marcus theory

Loeff, I.; Rabani, Joseph; Treinin, A.; Linschitz, Henry

doi:10.1021/ja00073a007

Cited by 95 publications

(115 citation statements)

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“…For 540 mM Cl reduction potentials of ∼1.6-1.8 V NHE , concurring with previous estimates based on 3 DOM* reactivity with phenols (1.36-1.95 V NHE ) (35). However, it is important to note that aromatic ketones, whose halide oxidation capability has been validated (4,5), may represent one of several components of 3 DOM*.…”

Section: Photochemical Generation Of Rhs Rhs Formation Via Halide Scsupporting

confidence: 90%

“…Secondly, direct halide oxidation by 3 DOM*, previously demonstrated using model triplet sensitizers (4,5), may provide a seawater-specific,…”

Section: Dom* Anmentioning

confidence: 99%

“…Transient spectroscopy demonstrated RHS formation from direct halide oxidation by synthetic aromatic ketone triplet sensitizers ( 3 SEN*) (4,5), which may represent a component of natural DOM triplet sensitizers. Aromatic ketone triplet sensitizers form a charge transfer complex (exciplex) with halides, resulting in 3 SEN* quenching to the ground state (SEN) or charge separation to produce RHS (Eqs.…”

Section: Photochemical Generation Of Rhs Rhs Formation Via Halide Scmentioning

confidence: 99%

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Halogen radicals contribute to photooxidation in coastal and estuarine waters

Parker

Mitch

2016

Proc. Natl. Acad. Sci. U.S.A.

194

220

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Although halogen radicals are recognized to form as products of hydroxyl radical (• OH) scavenging by halides, their contribution to the phototransformation of marine organic compounds has received little attention. We demonstrate that, relative to freshwater conditions, seawater halides can increase photodegradation rates of domoic acid, a marine algal toxin, and dimethyl sulfide, a volatile precursor to cloud condensation nuclei, up to fivefold. Using synthetic seawater solutions, we show that the increased photodegradation is specific to dissolved organic matter (DOM) and halides, rather than other seawater salt constituents (e.g., carbonates) or photoactive species (e.g., iron and nitrate). Experiments in synthetic and natural coastal and estuarine water samples demonstrate that the halide-specific increase in photodegradation could be attributed to photochemically generated halogen radicals rather than other photoproduced reactive intermediates [e. OH-independent pathway. Our results indicate that halogen radicals significantly contribute to the phototransformation of algal products in coastal or estuarine surface waters.halogen radicals | photochemistry | domoic acid | dimethyl sulfide | dissolved organic matter R esearch on the photochemical transformation of organic compounds in seawater has focused on freshwater-relevant pathways, including direct photolysis and dissolved organic matter (DOM)-sensitized indirect photodegradation by excited triplet state DOM ( 3 DOM*) or reactive oxygen species [e.g., hydroxyl radical ( • OH)] (1). High halide concentrations, the key characteristic distinguishing seawater from freshwater, are the predominant sink for• OH in seawater, with Br − scavenging ∼93% (Eq. 1) (2), resulting in an ∼40-fold reduction in• OH concentrations.• OH + BrThe role of the resultant Br• , as well as other radical reactive halogen species (RHS) (e.g., Cl ), in seawater photochemistry has received little attention. Here we evaluate the contribution of RHS, a family of photooxidants specific to seawater, to the photodegradation of important marine products for two reasons. Unlike diffusion-limited• OH rate constants, RHS rate constants with organic molecules span orders of magnitude (3), such that conversion of • OH to RHS focuses oxidation on more reactive molecules relative to bulk DOM. Secondly, direct halide oxidation by 3 DOM*, previously demonstrated using model triplet sensitizers (4, 5), may provide a seawater-specific,• OH-independent RHS production pathway that could increase overall radical generation rates.We investigated the importance of RHS for photooxidation of dienes and thioethers. Dienes occur in biomolecules (e.g., fatty acids) and in the marine algal toxin (6, 7), domoic acid (Fig. 1A, ii), where the diene contributes to toxicity (8). During summer 2015, a large bloom of the marine diatom Pseudo-nitzschia, extending from central California to Alaska, led to significant concern regarding the production of domoic acid, a potent neurotoxin (9). Consumption of mollusks and fish...

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Section: Photochemical Generation Of Rhs Rhs Formation Via Halide Scsupporting

confidence: 90%

“…Secondly, direct halide oxidation by 3 DOM*, previously demonstrated using model triplet sensitizers (4,5), may provide a seawater-specific,…”

Section: Dom* Anmentioning

confidence: 99%

Section: Photochemical Generation Of Rhs Rhs Formation Via Halide Scmentioning

confidence: 99%

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Halogen radicals contribute to photooxidation in coastal and estuarine waters

Parker

Mitch

2016

Proc. Natl. Acad. Sci. U.S.A.

194

220

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“…We attribute this phenomenon to side reactions involving the azide ion with 3 DOM. Loeff et al (1993) reported that azide and other anions are able to quench 9,10-anthroquinone sulfonate triplets through a charge transfer mechanism. The resulting azide radical could oxidize additional TMP as manifested by the observed more rapid reaction kinetics.…”

Section: Assessmentmentioning

confidence: 99%

Evaluating the triplet state photoreactivity of dissolved organic matter isolated by chromatography and ultrafiltration using an alkylphenol probe molecule

Cawley

Hakala

Chin

2009

Limnology & Ocean Methods

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The triplet state photochemistry of dissolved organic matter (DOM) isolated by XAD and C-18 chromatography and tangential flow ultrafiltration (TFUF) was investigated using 2,4,6 trimethylphenol (TMP) as a molecular probe. Water samples were taken from an Arctic seep adjacent the Oksrukuyik River (OKS) on the north slope of Alaska, USA, where DOM is derived primarily from allochthonous material and from a eutrophic midlatitude wetland, Old Woman Creek (OWC), in northern Ohio, USA, where the DOM is formed from both allochthonous and autochthonous precursors. DOM-mediated TMP photolysis occurred for all samples, but was significantly faster in the OWC isolates. The method used to isolate DOM also influenced TMP photoreactivity, whereby the C-18 and XAD isolated material were typically more reactive than ultrafiltered DOM. Analysis of the isolates by spectroscopy revealed that the materials isolated by chromatography were relatively enriched in aromatic constituents, while the TFUF fraction had the lowest aromaticity based on molar absorptivity at 280 nm. The fluorescence index values revealed differences between OKS and OWC, but no discernable trends were observed among isolates. This study shows that both the manner in which DOM is isolated and the composition of its precursors will influence its triplet state photoreactivity.

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“…[61] Photohydroxylation is suppressed by the addition of halide ions. [37,59,62,63] As short-lived intermediates CT-complexes have been suggested that can either decay to the ground state or, at elevated halide concentrations, form dihalide radical anions and a semiquinone radical anion, QC À . [62] Oxidation of carbonate to CO 3 C À has also been reported.…”

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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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Charge transfer and reactivity of n.pi.* and .pi..pi.* organic triplets, including anthraquinonesulfonates, in interactions with inorganic anions: a comparative study based on classical Marcus theory

Cited by 95 publications

References 0 publications

Halogen radicals contribute to photooxidation in coastal and estuarine waters

Halogen radicals contribute to photooxidation in coastal and estuarine waters

Evaluating the triplet state photoreactivity of dissolved organic matter isolated by chromatography and ultrafiltration using an alkylphenol probe molecule

Photohydroxylation of 1,4‐Benzoquinone in Aqueous Solution Revisited

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