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Potentiometric determination of pKa values of some quinolones in methanol-water and acetonitrile-water binary mixtures

Sardohan T., Kir E.

Chemia Analityczna

2009

Vol. 54, No. 4

629-643

pKa values of three quinolone compounds (ciprotloxacin, norfloxacin and enoxacin) in methanol—water (MeOH—water) and acetonitrile-water (ACN—water) mixtures were determined in potentiometric measurements. Standardization of the electrode system in MeOH-water and ACN-water mixtures was carried out potentiometncally by Gran's method. The obtained results were compared to the literature pKa values determined by various techniques and to the values predicted by the SPARC on-line pK 6calculator.

Wyznaczono metodą potencjometryczną wartości pKa trzech związków chinolonowych: ciprofloksacyny, norfloksacyny i enoksacyny. Pomiary wykonywano w roztworach: meta-nol-woda i acetonitryl-woda. Wzorcowanie układu elektrod w układach: MeOH-woda i ACN-woda wykonano potencjometrycznie metodą Grana. Wyniki porównano z literaturowymi wartościami pK awyznaczonymi za pomocą różnych metod jak również z wartościami obliczonymi za pomocą programu SPARC.

Spectrophootometric Studies of Acidity Constant and Cu2+ Ion Complexation of 1-Hydroxy-2-(prop-2'-enyl)-4-(prop-2'-enyloxy)-9,10-anthraquinone in Methanol-Water Mixtures

Shamsipur M.

Polish Journal of Chemistry

2001

Vol. 75, nr 10

1533-1541

The acidity constant of 1-hydroxy-2-(prop-2_-enyl)-4-(prop-2_-enyloxy)-9,10-anthraquinone in different methanol-water mixtures at 25_C has been determined spectrophotometrically. A linear reverse relationship is observed between the pKa and mole fraction of methanol in the solvent mixtures. The complexation reaction between the anthraquinone derivative used and Cu2+ ion has been studied in methanol solution at 25_C by a spectrophotometric technique. The stoichiometry of the resulting complex was found to be 1:1. The formation constant of the Cu2+-anthraquinone complex, evaluated from the computer fitting of the absorbance-mole ratio data at 5 different wavelengths, is log Kf = 4.59 _ 0.06.