Determination by Fluorimetric Titration of the Ionization Constants of Ciprofloxacin in Solution and in the Presence of Liposomes

• Published in: Photochemistry and photobiology Vol. 73; no. 1; pp. 14 - 19
• Main Authors: Luis Vázquez, José, Berlanga, Mercedes, Merino, Sandra, Domènech, Òscar, Viñas, Miquel, Teresa Montero, M., Hernández-Borrell, Jordi
• Format: Journal Article
• Language: English
• Published: United States 01.01.2001
• Subjects: Anti-Infective Agents - chemistry; Ciprofloxacin - analogs & derivatives; Ciprofloxacin - chemistry; Hydrogen-Ion Concentration; Liposomes; Photochemistry; PHOTOCHEMISTRY, PHOTOPHYSICS AND PHOTOTECHNOLOGY; Solutions; Spectrometry, Fluorescence; Static Electricity
• ISSN: 0031-8655; 1751-1097
• DOI: 10.1562/0031-8655(2001)073<0014:DBFTOT>2.0.CO;2

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.