title: Determination by fluorimetric titration of the ionization constants of ciprofloxacin in solution and in the presence of liposomes.
abstract: A fluorescence titration method was applied for the determination of pKa of ciprofloxacin (CPX) in solution. Values of 6.18 +/- 0.05 and 8.76 +/- 0.03 were obtained for pKa1 and pKa2, respectively. The method was used to determine the ionization constants in the presence of liposomes of dipalmitoylphosphatidylcholine (DPPC) and DPPC with 10 mol% of dipalmitoylphosphatidylglycerol. A dependence on the surface charge of liposomes was found which supported the existence of a basic electrostatic interaction between CPX and the phospholipid bilayer. Both pK values for the N-4 butyl-piperazinyl derivative (BCPX) of the parent compound were also determined in solution and in the presence of liposomes. The competition of both drugs for the same binding site as 1-anilino-8-naphtalene sulfonate demonstrate that the interaction is governed by electrostatic forces.
authors.affiliation: Laboratori V de Fisicoquímica, Facultat de Farmàcia, Barcelona, Spain.
authors.forename: J L
authors.initials: JL
authors.lastname: Vázquez
authors.forename: M
authors.initials: M
authors.lastname: Berlanga
authors.forename: S
authors.initials: S
authors.lastname: Merino
authors.forename: O
authors.initials: O
authors.lastname: Domènech
authors.forename: M
authors.initials: M
authors.lastname: Viñas
authors.forename: M T
authors.initials: MT
authors.lastname: Montero
authors.forename: J
authors.initials: J
authors.lastname: Hernández-Borrell
mesh_terms: D000890:Anti-Infective Agents / Q000737:chemistry; D002939:Ciprofloxacin / Q000031:analogs & derivatives / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008081:Liposomes; D010777:Photochemistry; D012996:Solutions; D013050:Spectrometry, Fluorescence; D055672:Static Electricity
chemical_list: D000890:Anti-Infective Agents; D008081:Liposomes; D012996:Solutions; D002939:Ciprofloxacin