The effect of β-cyclodextrin and pH on bifonazole hydrosolubility

Abstract

The equlibria of bifonazole in saturated water solution within the pH range 4 to 10 [I = 0.1 mol/dm3 (NaCl); 25 ºC] were studied spectrophotometrically. Based on the equlibrium constants determined in a heterogeneous system, the acidity constant (pKa = 5.72) and solubility in water (S=10-5.79+10-(pH + 0.07))were calculated. The influence of β-cyclodextrin on bifonazole solubility was examined in the presence of 10-3 and 10-4 mol/dm3 β-cyclodextrin. At pH values over 8, bifonazole solubility was two- and 13-fold increased in the presence of 10-4 and 10-3 mol/dm3 β-cyclodextrin respectively, compared to its solubility in water. The ratio of bifonazole solubility in the presence of β-cyclodextrin and that in water decreased in parallel to the increase of acidity.

Spektrofotometrijski su proučavane ravnoteže u zasićenom vodenom rastvoru bifonazola u pH intervalu 4–10. Na osnovu ravnotežnih konstanti određenih u heterogenom sistemu izračunata je kiselinska konstanta (pKa = 5,72) i rastvorljivost bifonazola u funkciji kiselosti rastvora (S=10-5.79+10-(pH + 0.07)) Uticaj β-ciklodekstrina (β-CD) na rastvorljivost ispitivan je u prisustvu 10-3 i 10-4 mol/dm3 β-CD. Utvrđeno je da pri pH vrednostima većim od 8 dolazi do povećanja rastvorljivosti 2 puta (u prisustvu 10-4 mol/dm3 β-CD) i 13 puta (u prisustvu 10-3 mol/dm3 β-CD) u odnosu na rastvorljivost bifonazola u vodi (u odsustvu β-CD). Odnos rastvorljivosti bifonazola u prisustvu β-CD i rastvorljivosti u vodi smanjuje se sa povećanjem kiselosti rastvora.