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Protolytic equilibria in homogeneous and heterogeneous aqueous systems of methyl- and propylparaben and influence of β-cyclodextrin on pKa values

Protolitičke ravnoteže u homogenim i heterogenim vodenim sistemima metil- i propilparabena i uticaj β -ciklodekstrina na pKa vrednosti

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2004
510.pdf (256.5Kb)
Authors
Popović, Gordana
Čakar, Mira
Article (Published version)
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Abstract
Acidity constants (Ka) and intrinsic hydrosolubility (Ks0) of two parabens, methylparaben and propylparaben, were spectrophotometrically determined at 25oC and a constant ionic strength of I=0.1 M (NaCl). Based on the determined equilibrium constants Ks0 and Ka, equilibrium constant Ks1 in heterogeneous system of methyl-and propylparaben was calculated. Solubility of the two parabens as a function of solution acidity was calculated applying the equation: s1 s0 3 [ ] S [H O ] K K + = + In addition, the effects of varying β-cyclodextrin concentrations on pKa values of the two parabens were examined. The results showed that β-CD influenced absorption spectra of the parabens (a decreased absorptivity and a bathochromic shift of the absorption maxima), but their pKa values remained almost unchanged.
Spektrofotometrijski su određene kiselinske konstante (Ka) i osnovna rastvorljivost (Ks0) u vodi metilparabena i propilparabena. Određivanja su vršena na temperaturi od 25 oC i pri konstantnoj jonskoj sili I=0.1 M (NaCl). Na osnovu određenih ravnotežnih konstanti Ks0 i Ka izračunata je ravnotežna konstanta Ks1 u heterogenom sistemu parabena. Rastvorljivost parabena u funkciji kiselosti rastvora izračunata je primenom jednačine 1 0 3 [ ] [ ] s s K S K H O+ = + Pored toga, ispitan je uticaj različitih koncentracija β-ciklodekstrina na pKa vrednosti datih parabena.
Keywords:
methylparaben / propylparaben / solubility / acidity constant / metilparaben / propilparaben / rastvorljivost / kiselinska konstanta
Source:
Arhiv za farmaciju, 2004, 54, 5, 601-611
Publisher:
  • Savez farmaceutskih udruženja Srbije, Beograd

ISSN: 0004-1963

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URI
http://farfar.pharmacy.bg.ac.rs/handle/123456789/512
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Pharmacy

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