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Subramanian, S.; Ferreira, Márcia M. C.; Trsic, Milan

doi:10.1023/a:1022487632133

Cited by 48 publications

(21 citation statements)

References 6 publications

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“…The kinetic measurements conducted with QRM showed that the apparent rate of reaction (2) increases when the pH is lowered, a fact which is in agreement with theoretical predictions for this type of redox process [34]. During the thin-film experiment, the situation is not the same.…”

Section: Resultssupporting

confidence: 82%

“…They also participate in the process of photosynthesis (hydroquinone plays the mediating role of agents in various reduction processes leading to the release of oxygen). In addition, quinones also display antioxidant properties in many biochemical systems [2][3][4][5][6][7][8]. It is known that, some alkalines, like magnesium and calcium, act as an essential co-factor in a number of biological systems, including the catalysis of oxygen evolution in photosynthesis [9].…”

Section: Introductionmentioning

confidence: 99%

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Characterization of lapachol in artificial organic-film membrane: Application for the trans-membrane transport of Mg2+

Ebelle

Nassi

Njanja

et al. 2010

Journal of Electroanalytical Chemistry

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Section: Resultssupporting

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Characterization of lapachol in artificial organic-film membrane: Application for the trans-membrane transport of Mg2+

Ebelle

Nassi

Njanja

et al. 2010

Journal of Electroanalytical Chemistry

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“…At physiological pH, isolapachol (2) is more acidic than lapachol (1), and the biologically inactive methylaminohydroxyquinones 3 and 4 are, to a large extent, zwitterionic. In all four compounds, the first pK a is related to the ionisation of the enol, and the differences in acidity of the -OH group may be explained in terms of the stabilisation of the enolate ion by hydrogen bonding.…”

Section: Discussionmentioning

confidence: 99%

“…Lapachol (1) possesses anti-tumour, antibiotic, antimalarial, anti-inflammatory and anti-ulcer properties, 1 whilst both 1 [2][3][4][5][6] and isolapachol (2) 4,6 exhibit significant activities against the etiological agents of a number of tropical diseases. Additionally, the 2-hydroxy-1,4-naphthoquinones 1 and 2 are potent molluscicides (Table 1) with activities against both mature adults and egg masses of Biomphalaria glabrata, 2,3,7 the intermediate host of the causative agent of schistosomiasis (Schistosoma mansoni).…”

Section: Introductionmentioning

confidence: 99%

Determination of the pKa values of some biologically active and inactive hydroxyquinones

Ossowski¹,

Goulart²,

Abreu³

et al. 2008

J. Braz. Chem. Soc.

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As constantes de dissociação aparentes (pK a ) de quatro 2-hidroxinaftoquinonas, diferentemente substituídas em C-3, foram determinadas em meio aquoso-etanólico (1:1, v/v), utilizando titulações pH-métricas e espectrofotométricas. O isolapachol (pK a <6) mostrou ser mais ácido que seu análogo natural, o lapachol, (pK a >6). Os derivados 3-metilaminados apresentam dois valores de pK a , um relacionado ao grupo enólico e o outro ao sal de amônio, e são zwitteriônicos, em larga extensão, em pH fisiológico. As possíveis conseqüências desses parâmetros frente a suas atividades biológicas são discutidas.The apparent dissociation constants (pK a ) of four 2-hydroxynaphthoquinones, differently substituted at C-3, were determined in water:ethanol (1:1, v/v) solutions by pH-metric and hybrid pH-metric/UV titration methods. Isolapachol (pK a < 6) was more acidic than lapachol (pK a > 6). Two pK a values were determined for each of the methylamino-derivatives investigated, the first relating to the enol function and the second to the ammonium salt. It was determined that under physiological pH, these derivatives would be to a large extension, zwitterionic. The possible effects of the measured parameters on the biological activities of the studied compounds are discussed.

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“…Quinones show several biological and pharmacological activities, [1][2][3][4][5][6][7][8][9] with their mechanism of action being related to redox cycling, which leads to the formation of reactive oxygen species that can damage cellular macromolecules. 10,11 The quinone cytotoxicity to many human cancer cell lines is amply recognized, [12][13][14][15][16][17] acting through inhibition of DNA repair enzymes, 18 inhibition or activation of DNA topoisomerase I, 17,19 induction of Vol.…”

Section: Introductionmentioning

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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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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Cited by 48 publications

References 6 publications

Characterization of lapachol in artificial organic-film membrane: Application for the trans-membrane transport of Mg2+

Characterization of lapachol in artificial organic-film membrane: Application for the trans-membrane transport of Mg2+

Determination of the pKa values of some biologically active and inactive hydroxyquinones

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

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