Oxygen Quenching of Excited Aliphatic Ketones and Diketones

Nau, Werner M.; Scaiano, J. C.

doi:10.1021/jp960932i

Cited by 91 publications

(66 citation statements)

References 69 publications

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“…This high value is fully in accord with earlier suggestions [48][49][50][51][52][53] that a pp* triplet is required for highly efficient singlet oxygen formation. Similar values were reported for other b-lapachones.…”

Section: Laser Flash Photolysis Studiessupporting

confidence: 92%

The photochemical reactivity of triplet β-lapachone-3-sulfonic acid towards biological substrates

Netto‐Ferreira¹,

Lhiaubet‐Vallet²,

Silva³

et al. 2010

J. Braz. Chem. Soc.

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A reatividade fotoquímica do ácido 3-sulfônico da b-lapachona (1) frente a amino ácidos, bases nucleicas ou nucleosídeos foi determinada empregando a técnica de fotólise por pulso de laser de nanossegundo. A excitação (l = 355 nm) de soluções deaeradas de 1, em acetonitrila, resultou na formação do seu estado excitado triplete, o qual foi suprimido eficientemente por L-triptofano, éster metílico de L-triptofano, L-tirosina, éster metílico de L-tirosina e éster metílico de L-cisteína (k q ≅ 10 9 L mol -1 s -1). Para L-triptofano, L-tirosina e seus ésteres metílicos novos transientes foram formados no proceso de supressão, os quais foram atribuídos ao par de radicais resultante de uma transferência inicial de elétron do amino ácido, ou dos seus ésteres metílicos, à quinona excitada, seguida por uma transferência de próton rápida. Não foi possível a obtenção de constantes de velocidade de supressão para timina e timidina, em acetonitrila, o que pode ser devido tanto ao caráter p p* de 1 quanto ao baixo valor para a sua energia triplete. Por outro lado, a supressão de 1 por 2'-deoxaguanosina foi tão eficiente quanto para triptofano ou tirosina (k q ≅ 10 9 L mol -1 s -1). O rendimento quântico para a formação de oxigênio singlete ( 1 O 2 ) a partir de 1 foi determinado empregando-se estudos de emissão resolvida no tempo na região do infravermelho próximo, tendo-se obtido um valor consideravelmente alto para este rendimento quântico (F D = 0,7).The photochemical reactivity of b-lapachone-3-sulfonic acid (1) towards amino acids, nucleobases or nucleosides has been examined employing the nanosecond laser flash photolysis technique. Excitation (l = 355 nm) of degassed solutions of 1, in acetonitrile, resulted in the formation of its corresponding triplet excited state. This transient was efficiently quenched by L-tryptophan, L-tryptophan methyl ester, L-tyrosine, L-tyrosine methyl ester and L-cysteine methyl ester (k q ≅ 10 9 L mol -1 s -1). For L-tryptophan, L-tyrosine and their methyl esters new transients were formed in the quenching process, which were assigned to the corresponding radical pairs resulting from an initial electron transfer from the amino acids, or their esters, to the excited quinone, followed by a fast proton transfer. No measurable quenching rate constants could be observed in the presence of thymine or thymidine, in acetonitrile solution, which is probably due to the p p* character of triplet 1 as well as to its low triplet energy. On the other hand, the rate constant obtained when 1 was quenched by 2'-deoxyguanosine is reasonably fast (k q ≅ 10 9 L mol -1 s -1). The quantum efficiency of singlet oxygen ( 1 O 2 ) formation from 1 was determined employing time-resolved near-IR emission studies upon laser excitation and showed a considerably high value (F D = 0.7).Keywords: laser flash photolysis, ortho-quinones, triplet excited state, coupled electron/ proton transfer IntroductionQuinones show several biological and pharmacological activities, 1-9 with their mechanism of action being related to redo...

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Section: Laser Flash Photolysis Studiessupporting

confidence: 92%

The photochemical reactivity of triplet β-lapachone-3-sulfonic acid towards biological substrates

Netto‐Ferreira¹,

Lhiaubet‐Vallet²,

Silva³

et al. 2010

J. Braz. Chem. Soc.

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“…the specific quenching efficiency of the oxygen molecule is an order of magnitude higher than in case of the singlet excited state. The T 1 + 3 O 2 → S 0 + O 2 ( 1 ∆ g ) reaction is spinallowed (to the extent of 1/9 spin-statistic factor) [15]. In contrast, the S 1 + 3 O 2 → S 0 + O 2 ( 1 ∆ g ) reaction is undoubtedly spin-forbidden, and so the possible alternative energy transfer process considered here does not seem to be very effective, either [15].…”

Section: Photophysical Studiesmentioning

confidence: 81%

Photochemical and photophysical study on the kinetics of the atmospheric photodissociation of acetone

Szilágyi

Kovács

et al. 2009

React Kinet Catal Lett

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The pressure dependence of the photodissociation quantum yield of acetone has been determined in different buffer gases at 308 nm. Results by Stern-Volmer analyses are in accordance with a suggested photolysis mechanism. Luminescence spectra, lifetimes and transition dipole moments have been determined. The energy transfer process by O 2 to give O 2 ( 1 ∆ g ) is of minor importance in the case of the singlet excited state of acetone, while it is the dominant deactivation process for the triplet state.

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“…•− was observed. Since the oxygen quenching of the singlet or/and triplet excited states of organic molecules to yield 1 O 2 has been extensively reported [22], it was suggested that the generation of 1 O 2 in this photochemical reaction of TC was reasonably attributable to the same mechanism. The fluorescence emission of TC aqueous solution before and after bubbling with argon did not change appreciably (data not shown), so the singlet TC excited state was not responsible for the generation of 1 O 2 and the quenching of triplet TC excited was suggested to yield 1 O 2 in this system.…”

Section: Mechanism On Photolysis Of Tcmentioning

confidence: 92%

Photodegradation of tetracycline and formation of reactive oxygen species in aqueous tetracycline solution under simulated sunlight irradiation

Chen

et al. 2008

Journal of Photochemistry and Photobiology A: Chemistry

257

102

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The photochemical kinetics and mechanism of the antibiotic compound tetracycline (TC) was investigated in aqueous solution under simulated sunlight irradiation. The study of the electron spin resonance revealed that the singlet oxygen ( 1 O 2 ) was generated and the formation rate decreased with increasing pH in illuminated TC solution. Also, it was found that the H 2 O 2 was produced and increased with increasing pH under the simulated sunlight irradiation. The results verified that TC could be sunlight excited and induced the formation of reactive oxygen species. Moreover, the contributions of oxidation reaction to photodegradation of TC were clarified by the role of different radical scavengers. The kinetic model elucidated the involvement of TC photoinduced singlet oxygen on the photodegradation of TC. It was verified that the photodegradation of TC was predominantly attributed to direct photolysis. The quantum yields of direct photolysis increases with increasing pH in the range of 6.0-9.0, varying from 3.4 × 10 −4 to 1.1 × 10 −2 . The indirect photolysis of TC was carried out in the presence of nitrate, bicarbonate, ferric ions and humic acid (HA), respectively. The results verified that the photodegradation of tetracycline was not obviously affected by these photosensitizers except ferric ions, indicating that the direct photolysis of TC was predominant process.

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Oxygen Quenching of Excited Aliphatic Ketones and Diketones

Cited by 91 publications

References 69 publications

The photochemical reactivity of triplet β-lapachone-3-sulfonic acid towards biological substrates

The photochemical reactivity of triplet β-lapachone-3-sulfonic acid towards biological substrates

Photochemical and photophysical study on the kinetics of the atmospheric photodissociation of acetone

Photodegradation of tetracycline and formation of reactive oxygen species in aqueous tetracycline solution under simulated sunlight irradiation

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