Laser flash photolysis study of the triplet reactivity of β-lapachones

Netto‐Ferreira, José Carlos; Bernardes, Bauer de Oliveira; Ferreira, Aurélio B. B.; Miranda, Miguel A.

doi:10.1039/b716104b

Cited by 19 publications

(29 citation statements)

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“…This could be related to the fact that one of the proposed mechanisms for the cytotoxic action of quinones involves the alkylation of thiol groups on the thiol-containing enzymes. 44 This same mechanism could be operating in the quenching of the triplet excited state of b-lapachone-3-sulfonic acid, which would explain the lack of observation of the semiquinone radical.As previously reported by our group, triplet 1 has pp* configuration 23 The Photochemical Reactivity of Triplet b-Lapachone-3-sulfonic Acid J. Braz. Chem.…”

supporting

confidence: 57%

“…6, 2010 topoisomerase IIa-mediated DNA breaks, 20 and inhibition of poly(ADP-ribose) polymerase-1. 21 More recently, Boothman and co-workers 23 have clearly demonstrated that b-lapachone, an ortho-quinone, activates a novel apoptotic response in a number of cell lines. It was shown that the enzyme NAD(P)H:quinone oxidoreductase (NQO1) substantially enhances the toxicity of b-lapachone in a number of tumor types (i.e., breast, pancreatic, colon, prostate and lung) and during neoplastic transformation.…”

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confidence: 99%

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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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confidence: 57%

mentioning

confidence: 99%

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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“…This mechanism, shown in Scheme 1, involves an initial electron transfer from the phenol to the excited ketone, through an intermediate exciplex, followed by an ultrafast proton transfer, which ultimately results in the formation of the radical pair ketyl/ phenoxyl. [1][2][3][4][5][6][7][8] In support to this mechanism, Figure 4 shows a representative spectrum obtained after laser irradiation of a deoxygenated solution of thiochromanone (1) acetonitrile. In this spectrum the absorptions relative to triplet 1 were substituted for new ones in the 340-440 nm region, which can be associated to a mixture of the ketyl radical 2 derived from the thiochromanone triplet, as well as to the 4-methoxyphenoxyl radical, which shows absorption at 405 nm 41 (Scheme 1).…”

Section: Resultsmentioning

confidence: 94%

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] The mechanism for this process is now well established and involves the initial formation of a hydrogen-bonded exciplex in the triplet excited state, followed by electron transfer and, subsequently, an ultrafast proton transfer. 4,[9][10][11][12][13][14][15][16] DFT calculations clearly showed that for the triplet complex (exciplex) ketone-phenol the hydrogen transfer is predominantly occurring.…”

Section: Introductionmentioning

confidence: 99%

Phenolic hydrogen abstraction by the triplet excited state of thiochromanone: a laser flash photolysis study

Ribeiro¹,

Bertoti²,

Netto‐Ferreira³

2010

J. Braz. Chem. Soc.

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O estado excitado triplete de cetonas pode oxidar substratos biológicos acarretando danos a diversas biomoléculas como aminoácidos, nucleosídeos e mesmo DNA. Como parte de nossos estudos acerca da interação entre carbonilas e fenóis, foi investigada a reatividade do estado excitado triplete de tiocromanona (1) frente a fenóis, em acetonitrila, empregando a técnica de fotólise por pulso de laser de nanossegundo. As constantes de velocidade de supressão obtidas variaram de (1,1 ± 0,1) × 10 8 L mol -1 s -1 (4-cianofenol) a (5,8 ± 1,0) × 10 9 L mol -1 s -1 (hidroquinona). Um gráfico de Hammett para a reação do triplete de 1 com uma série de fenóis contendo substituintes polares resultou em uma constante de reação r = -0,90. Este valor negativo para a constante de reação r está plenamente de acordo com um mecanismo envolvendo uma transferência acoplada elétron/ próton no processo de transferência de hidrogênio do fenol para a carbonila triplete.Triplet ketones are known to oxidize biological substrates which can lead to damage of several biomolecules such as amino acids, nucleosides and DNA. As part of our systematic study on the interaction between carbonyl compounds and phenols, the triplet reactivity of thiochromanone (1) towards substituted phenols, in acetonitrile, was investigated employing the laser flash photolysis technique. The quenching rate constants ranged from (1.1 ± 0.1) × 10 8 L mol -1 s -1 (4-cyanophenol) to (5.8 ± 1.0) × 10 9 L mol -1 s -1 (hydroquinone). A Hammett plot for the reaction of triplet 1 with phenols containing polar substituents resulted in a reaction constant r = -0.90. This negative value observed for the reaction constant r is in accord with a mechanism in which the hydrogen transfer from phenols to the triplet carbonyl involves a coupled electron/proton transfer.Keywords: thiochromanone, laser flash photolysis, triplet excited state, hydrogen donors IntroductionIn the last few years the phenolic hydrogen abstraction by carbonyl compounds in the triplet excited state has been extensively studied employing experimental and theoretical methods. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] The mechanism for this process is now well established and involves the initial formation of a hydrogen-bonded exciplex in the triplet excited state, followed by electron transfer and, subsequently, an ultrafast proton transfer. 4,9-16 DFT calculations clearly showed that for the triplet complex (exciplex) ketone-phenol the hydrogen transfer is predominantly occurring. 8 The very fast quenching rate constants of triplet carbonyls towards phenols is consequence of both the low reduction potential of the former as well as the low oxidation potential of the later. 4,16 Experimentally, this coupled electron/proton transfer mechanism ultimately results in the formation of the ketyl-aryloxyl radical pair.Triplet ketones are known to oxidize biological substrates such as amino acids, nucleosides and DNA. Due to this, topical or systemic administration of drugs containing the carbonyl chromophore c...

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“…36 The results showed that formaldehyde, acetone, and cyclohexanone have a high grafting efficiency, especially acetone which gives the highest grafting efficiency. The reaction of phenols as efficient inhibitors implies two facts: the H atoms in PhOH have a high reactivity to readily be abstracted [37][38][39] and the formed PhOÁradicals have a strong ability to scavenge carbon-centered chain radicals. 40 In this work, acetone as photoinitiator and different phenols [including 4-hydroxylbenzene sulfonic acid (HBSA), p-aminophenol, tyramine, and 4-hydroxythiophenol and tyrosine] with a para substituent XR (denoted XRPhOH) as the reactants were proposed to incorporate a broad range of functional X groups with an R spacer onto the polymeric surface as illustrated in Scheme 1.…”

Section: Resultsmentioning

confidence: 99%

Functionalization of polymeric surfaces by simple photoactivation of CH bonds

Xie

et al. 2011

J. Polym. Sci. A Polym. Chem.

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A universal photoassisted pathway to functionalize polymeric surfaces is presented by transferring the inert surface sp3 CH bonds into reactive groups, such as SO3H, NH2, SH, and COOH. The proposed method uses acetone as photoinitiator and different phenols with a para substituent XR as the reactants. Acetone excited by UV irradiation acts as a pair of scissors cutting both the surface CH bonds of the polymer substrate and the OH bonds of phenol, leading to the formation of carbon‐centered surface chain free radicals and oxygen‐centered phenoxy free radicals. By coupling of these two radicals, a variety of functional X groups with an R spacer from XR species of different phenol reactants were readily bonded to the polymeric surfaces, where phenol reactants included 4‐hydroxylbenzene sulfonic acid for SO3H, p‐aminophenol and tyramine for NH2, 4‐hydroxythiophenol for SH, and tyrosine for COOH. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

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Laser flash photolysis study of the triplet reactivity of β-lapachones

Cited by 19 publications

References 48 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

Phenolic hydrogen abstraction by the triplet excited state of thiochromanone: a laser flash photolysis study

Functionalization of polymeric surfaces by simple photoactivation of CH bonds

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