QUENCHING OF TRIPLET BENZOPHENONE BY VITAMINS E and C and BY SULFUR CONTAINING AMINO ACIDS and PEPTIDES

Encinas, M. V.; Lissi, E. A.; Olea, Andrés F.

doi:10.1111/j.1751-1097.1985.tb01580.x

Cited by 53 publications

(33 citation statements)

References 39 publications

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“…This has important implications for the chemistry in the MBL, because the activation of halides in seawater containing chlorophyll or organic carbonyl provides a catalytic loss mechanism for ozone. The latest measurements (Environmenta, 2009) show that the halogen may cause to decreasing ozone levels in the lower atmosphere over tropical oceans and probably above most other oceans. Indeed, the source of tropospheric gas-phase halogen is known to be heterogeneous in nature (E. M. Knipping et al, 2000).…”

Section: Discussionmentioning

confidence: 99%

“…Numerous studies on aromatic ketones on photoinduced charge transfer or/and energy transfer (Benitez et al, 1997;Haag et al, 1984;Huang and Shu, 1995;Poznyak and Vivero, 2005;Wu and Masten, 2002). In this case, following light absorption, benzophenone is capable of generating reactive oxidant species, such as singlet oxygen O 2 ( 1 g ) (Mehrdad et al, 2002a b), ketyl radical and others, which can oxidize a wide range of organic compounds (Blanchi and Watkins, 1974;Encinas et al, 1985;Encinas and Scaiano, 1981;Grewer and Brauer, 1994;Haselbach et al, 1991;Jacques et al, 1997;Kajii et al, 1987). This is especially relevant for the fate of organic matter in aquatic environments (Haag et al, 1984).…”

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confidence: 99%

“…In the present study benzophenone (BP) has been selected as a proxy for the aromatic carbonyl found in sea surface microlayer. Excited triplet states of aromatic ketones have been widely studied in photochemistry (Blanchi and Watkins, 1974;Encinas et al, 1985;Encinas and Scaiano, 1981;Grewer and Brauer, 1994;Haselbach et al, 1991;Jacques et al, 1997;Kajii et al, 1987). Photochemical transformations may occur as a result of absorption of light or via sensitized reactions.…”

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Photoinduced oxidation of sea salt halides by aromatic ketones: a source of halogenated radicals

et al. 2009

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Abstract.The interactions between triplet state benzophenone and halide anion species (Cl − , Br − and I − ) have been studied by laser flash photolysis (at 355 nm) in aqueous solutions at room temperature. The decay of the triplet state of benzophenone was followed at 525 nm. Triplet lifetime measurements gave rate constants, k q (M −1 s −1 ), close to diffusion controlled limit for iodide (∼8×10 9 M −1 s −1 ), somewhat less for bromide (∼3×10 8 M −1 s −1 ) and much lower for chloride (<10 6 M −1 s −1 ). The halide (X − ) quenches the triplet state; the resulting product has a transient absorption at 355 nm and a lifetime much longer than that of the benzophenone triplet state, is formed. This transient absorption feature matches those of the corresponding radical anion (X − 2 ). We therefore suggest that such reactive quenching is a photosensitized source of halogen in the atmosphere or the driving force for the chemical oxidation of the oceanic surface micro layer.

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Section: Discussionmentioning

confidence: 99%

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Photoinduced oxidation of sea salt halides by aromatic ketones: a source of halogenated radicals

et al. 2009

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“…It may involve either energy transfer from the excited quinone to the thioether or hydrogen atom transfer from the thioether a hydrogen to the triplet quinone (reaction (8)). A similar quenching mechanism has been previously proposed for the quenching of triplet benzophenone by GSSG (oxidized glu-ANDERS BRUNMARK tathione) (Encinas et al, 1985) as well as several sulphides (Inbar et al, 1982).…”

Section: Ohmentioning

confidence: 66%

“…On the other hand, several cellular antioxidant molecules show a high reactivity against excited triplet ketones. Triplet ketones react with ascorbic acid, vitamin E and GSH with second order rate constants of 1.2-, 6.7-and 0.67 X 10" M-'s-', respectively (Encinas et al, 1985). The oxygen addition reactions resulting in the formation of epoxy and hydroxy adducts of p-benzoquinone may also be of toxicological interest.…”

Section: Commentsmentioning

confidence: 99%

Formation of electronically excited states during the interaction ofp‐benzoquinone with hydrogen peroxide

Brunmark

1989

J. Biolumin. Chemilumin.

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The reaction between p-benzoquinone and H2O2 in slightly alkaline solutions yields three major quinoid products that accumulate in the reaction mixture: (a) 2,3-epoxy-p-benzoquinone, (b) 2-hydroxy-p-benzoquinone and (c) p-benzohydroquinone. The reaction is accompanied by photoemission, probably originating from excited triplet 2-hydroxy-p-benzoquinone. These products originate from hydrogen peroxide and hydroxide nucleophilic addition to the C2 = C3 double bond, as well as secondary redox interactions. The hydroxy substituent and the epoxide ring exert a substantial influence on the electronic distribution in the p-benzoquinone molecule leading to a decrease in the half-wave potential, as compared to the parent p-benzoquinone. The generation of electronically excited states is the result of reactions secondary to the nucleophilic additions involving 2-hydroxy-p-benzosemiquinone, H2O2 and hydroxyl radical. The process involves the primary oxidation of 2-hydroxy-p-benzosemiquinone by hydrogen peroxide, followed by oxidation of the semiquinone by hydroxyl radical leading to the formation of the electronically excited quinone. The decay of the excited triplet to the ground state is accompanied by photoemission with maximal intensity at 485-530 nm. Thermodynamic calculations along with an observed increase of photoemission intensity in anaerobiosis point to the triplet (n, pi*) multiplicity of the excited state. The efficiency of chemiluminescence could be calculated as 10(-8) photons/2-hydroxy-p-benzoquinone molecule formed. Photoemission arising from the p-benzoquinone/H2O2 reaction was inhibited efficiently by addition of GSH to the reaction mixture. This may be due to deactivation of the triplet quinone by a 2-glutathionyl-p-benzohydroquinone adduct, involving thioether alpha-hydrogen atom-transfer to the triplet ketone.

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Photochemical Deracemization of N‐Carboxyanhydrides En Route to Chiral α‐Amino Acid Derivatives

Iglhaut,

Freund,

Bach

2024

Angewandte Chemie

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Readily accessible, racemic N‐carboxyanhydrides (NCAs) of α‐amino acids underwent a deracemization reaction upon irradiation at λ = 366 nm in the presence of a chiral benzophenone catalyst. The enantioenriched NCAs (up to 98% ee) serve as activated α‐amino acid surrogates and, due to their instability, they were directly converted into consecutive products. N‐Protected α‐amino acid esters were obtained after reaction with MeOH and N‐benzoylation (14 examples, 70%‐quant., 82‐96% ee). Other consecutive reactions included amide (ten examples, 65%‐quant., 90‐98% ee) and peptide (three examples, 75‐89%, d.r. = 97/3 to 94/6) bond formation. Limitations of the method relate for some NCAs to issues with solubility, photooxidation, and high configurational lability.

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QUENCHING OF TRIPLET BENZOPHENONE BY VITAMINS E and C and BY SULFUR CONTAINING AMINO ACIDS and PEPTIDES

Cited by 53 publications

References 39 publications

Photoinduced oxidation of sea salt halides by aromatic ketones: a source of halogenated radicals

Photoinduced oxidation of sea salt halides by aromatic ketones: a source of halogenated radicals

Formation of electronically excited states during the interaction ofp‐benzoquinone with hydrogen peroxide

Photochemical Deracemization of N‐Carboxyanhydrides En Route to Chiral α‐Amino Acid Derivatives

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