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

The apparent dissociation constants (pKa) 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 (pKa < 6) was more acidic than lapachol (pKa > 6). Two pKa value...

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Bibliographic Details
Published in:Journal of the Brazilian Chemical Society 2008, Vol.19 (1), p.175-183
Main Authors: Ossowski, Tadeusz, Goulart, Marília O. F., Abreu, Fabiane C. de, Sant’Ana, Antônio Euzébio G., Miranda, Paulo Rogério B., Costa, Cicero de Oliveira, Liwo, Adam, Falkowski, Piotr, Zarzeczanska, Dorota
Format: Article
Language:English
Subjects:
CHEMISTRY, MULTIDISCIPLINARY
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Summary:The apparent dissociation constants (pKa) 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 (pKa < 6) was more acidic than lapachol (pKa > 6). Two pKa 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.
ISSN:0103-5053
1678-4790
DOI:10.1590/S0103-50532008000100025