Mercury photoreduction and photooxidation in lakes: Effects of filtration and dissolved organic carbon concentration.

Mercury is a globally distributed, environmental contaminant. Quantifying the retention and loss of mercury is integral for predicting mercury-sensitive ecosystems. There is little information on how dissolved organic carbon (DOC) concentrations and particulates affect mercury photoreaction kinetics in freshwater lakes.

Photocyclization and Photoaddition Reactions of Arylphenols via Intermediate Quinone Methides.

A series of five benzannelated derivatives of 2-phenylphenol were prepared, and their photochemistry was investigated. Two of these (3-phenyl-2-naphthol, 10, and 1-phenyl-2-naphthol, 11) were photoinert. For 2-(1-naphthyl)phenol (12) and 1-(1-naphthyl)-2-naphthol (13), ESPT took place to either the 2'-position or the 7'-position of the naphthalene ring to give quinone methides (QMs) that underwent either reverse proton transfer (RPT) or electrocyclic ring closure to give dihydrobenzoxanthenes.

Photodecaging from 9-substituted 2,7-dihydroxy and dimethoxyfluorenes: competition between heterolytic and homolytic pathways.

2,7-Dihydroxy-9-fluorenol (9), 2,7-dimethoxy-9-fluorenol (10), and 2,7-dimethoxy-9-acetoxyfluorene (11) were prepared and their photochemistry was studied in methanol and aqueous methanol solution in the hopes of observing efficient expulsion of the substituents positioned at the 9-position. For all three compounds, the primary photoproducts were 2,7-disubstituted-9-fluorenes and 2,7-disubstituted-9-methoxyfluorenes. A mechanism of reaction is proposed for production of these products, and involves competing homolytic and heterolytic pathways that produce radical and carbocation intermediates.

Efficient photodecarboxylation of trifluoromethyl-substituted phenylacetic and mandelic acids.

A total of eight CF(3)-substituted phenylacetic and mandelic acids are shown to undergo efficient photodecarboxylation (PDC; Phi = 0.37-0.74) in basic aqueous solution to give the corresponding trifluoromethyltoluenes or trifluoromethylbenzyl alcohols.

How drug photodegradation studies led to the promise of new therapies and some fundamental carbanion reaction dynamics along the way.

The photodegradation of nonsteroidal anti-inflammatory drugs (NSAIDs), a class of medications that includes aspirin and ibuprofen, has generated considerable interest since the 1990s, largely because of the phototoxic and photoallergic effects that frequently accompany their therapeutic use. Among NSAIDs, ketoprofen, which contains a benzophenone chromophore, has been extensively studied, reflecting both its notorious adverse effects and the fascination that photochemists have with benzophenone. The photochemistry of ketoprofen involves the intermediacy of an easily detectable carbanion with a remarkable lifetime of 200 ns in water; its life expectancy can in fact be extended to minutes under carefully controlled anhydrous conditions.

Photolabile protecting groups based on the singlet state photodecarboxylation of xanthone acetic acid.

A new photolabile protecting group (PPG) for carboxylic acids and amines has been developed based on the rapid singlet state photodecarboxylation of xanthone acetic acids with several features that are superior to many other systems. We demonstrate that the "xanthonate" PPG can photorelease carboxylic acids and amines (via the carbamates) quantitatively in neutral phosphate buffer solution with a remarkable "uncaging cross section" (Phi x epsilon = 3900 M(-1) cm(-1) with UVA irradiation). Advantageous features include a high reaction efficiency (Phi > 0.

A simple and smart oxygen sensor based on the intrazeolite reactions of a substituted anthraquinone.

Inclusion of 2-(hydroxymethyl)anthraquinone in zeolite NaY leads to a solid, photoactivated, reusable oxygen sensor capable of reporting and memorizing oxygen contamination events by simple visual inspection.

Photodecarboxylation of xanthone acetic acids: C-C bond heterolysis from the singlet excited state.

[reaction: see text] Irradiation of 2- and 4-xanthone acetic acid in aqueous buffer (pH 7.4) leads to efficient (Phi = 0.67 and 0.

Formal intramolecular photoredox chemistry of meta-substituted benzophenones.

[reaction: see text]. Photolysis of 3-(hydroxymethyl)benzophenone (1) in aqueous solution (pH < 3) results in clean formation of 3-formylbenzhydrol (2) at dilute (<10(-4) M) conditions. Evidence suggests that the highly efficient (Phi approximately 0.

Photogeneration and chemistry of biphenyl quinone methides from hydroxybiphenyl methanols.

The photosolvolysis of several biphenyl methanols (Ph-PhCH[Ph]OH) substituted with hydroxy or methoxy groups on the benzene ring not containing the -CH(Ph)OH moiety has been studied in aqueous solution. This work is a continuation of our studies of photosolvolysis of hydroxy-substituted arylmethanols that generate quinone methide intermediates, some of which are known to be relevant intermediates in toxicology and in biological and organic chemistry in general. In this study, we further probe the ability of the biphenyl ring system to transmit charge from the ring substituted with a potential electron-donating group (hydroxy and methoxy) to the adjacent benzene ring that contains a labile benzyl alcohol moiety.

Carbanion-mediated photocages: rapid and efficient photorelease with aqueous compatibility.

A new photocage is proposed, based on ketoprofen-derived compounds and mediated by carbanions. The new photocage has significant advantages over the widely used o-nitrobenzyl derivatives, including aqueous compatibility, faster photorelease, higher quantum yield, and innocuous byproducts. The photorelease of ibuprofen illustrates the properties of the new photocage.

Photoaddition of water and alcohols to the anthracene moiety of 9-(2'-hydroxyphenyl)anthracene via formal excited state intramolecular proton transfer.

The title compound undergoes efficient photoaddition of a molecule of a hydroxylic solvent (H(2)O, MeOH, (Me)(2)CHOH) across the 9- and 10-positions of the anthracene moiety to give isolable triphenylmethanol or triphenylmethyl ether type products. The reaction is believed to proceed via a mechanism involving water-mediated formal excited state intramolecular proton transfer (ESIPT) from the phenolic OH to the 10-position of the anthracene ring, generating an o-quinone methide intermediate that is observable by nanosecond laser flash photolysis, and is trappable with nucleophiles. A "water-relay" mechanism for proton transfer seems plausible but cannot be proven directly with the data available.

An antenna triplet sensitiser for 1-acyl-7-nitroindolines improves the efficiency of carboxylic acid photorelease.

Conjugates of a triplet sensitiser (a 4,4'-dialkoxybenzophenone) with 1-acetyl-7-nitroindolines show up to 20-fold enhancement for photorelease of acetate (relative to the same indolines lacking the attached sensitiser) upon irradiation at 300 nm in neutral aqueous solution. The sensitised photolysis can be carried out in the presence of dissolved oxygen and will be applicable to photorelease of other carboxylates. The enhanced efficiency is mediated by an antenna function of the sensitiser, which transfers its triplet energy to populate the reactive, short-lived triplet state of the acylnitroindoline.

Photohydration and photosolvolysis of biphenyl alkenes and alcohols via biphenyl quinone methide-type intermediates and diarylmethyl carbocations.

Evidence is presented for the photochemical generation of novel biphenyl quinone methide (BQM)-type intermediates on photolysis of hydroxybiphenyl alkenes 7 and 8 and hydroxybiphenyl alcohols 9 and 10. Mechanistic investigations utilizing product, fluorescence, and nanosecond laser flash photolysis (LFP) studies indicate two distinct pathways for the formation of these BQMs depending upon the functional groups of the progenitor. Formal excited-state intramolecular proton transfer (ESIPT) between the phenol and the alkene led to BQMs upon irradiation of the hydroxybiphenyl alkenes 7 and 8, while excited-state proton transfer (ESPT) to solvent followed by dehydroxylation was responsible for BQM formation from the hydroxybiphenyl alcohols 9 and 10.

Excited-state intramolecular proton transfer in o-hydroxybiaryls: a new route to dihydroaromatic compounds.

An excited-state intramolecular proton transfer (ESIPT) from the phenol OH to the 7'-carbon on the naphthyl ring in o-(1-naphthyl)phenol (3) and 1-(1'-naphthyl)-2-naphthol (4) leads to efficient (Phi = 0.1-0.2) formation of the corresponding dihydrobenzoxanthenes (5 and 7) via quinone methide intermediates.

A new type of excited-state intramolecular proton transfer: proton transfer from phenol OH to a carbon atom of an aromatic ring observed for 2-phenylphenol.

The photochemical deuterium incorporation at the 2'- and 4'-positions of 2-phenylphenol (4) and equivalent positions of related compounds has been studied in D(2)O (CH(3)OD)-CH(3)CN solutions with varying D(2)O (CH(3)OD) content. Predominant exchange was observed at the 2'-position with an efficiency that is independent of D(2)O (MeOD) content. Exchange at the 2'-position (but not at the 4'-position) was also observed when crystalline samples of 4-OD were irradiated.

Excited state intramolecular redox reaction of 2-(hydroxymethyl)anthraquinone in aqueous solution.

The title compound undergoes a novel excited state intramolecular redox reaction in which the 'distal' side chain benzylic alcohol is oxidized to the aldehyde and the carbonyl moieties of anthraquinone reduced, with evidence suggesting that the primary photochemical process is a deprotonation of the benzylic C-H proton (by water) mediated by the solvent.