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.
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1 January 2001
Determination by Fluorimetric Titration of the Ionization Constants of Ciprofloxacin in Solution and in the Presence of Liposomes
José Luis Vázquez,
Mercedes Berlanga,
Sandra Merino,
Òscar Domènech,
Miquel Viñas,
M. Teresa Montero,
Jordi Hernández-Borrell
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Photochemistry and Photobiology
Vol. 73 • No. 1
January 2001
Vol. 73 • No. 1
January 2001