Determination of thermodynamic protonation constants of some antimicrobial agents by HPLC method

Antimicrobial agents are therapeutic substances with a wide range of uses, including antiseptics, antibiotics, antivirals, antifungals and antiparasitics. These substances are used to prevent or treat infections. Antimicrobials, especially heterocyclic structures containing nitrogen atoms, are widely used in many natural products and synthetic drugs due to their ability to exhibit a wide range of pharmacological activities. Since clotrimazole, sertaconazole, oxiconazole and klimbazole, which are widely used among these drugs, have weak acid/base properties, it is necessary to examine the acid-base balance of these molecules in aqueous environment and understand the activities of the molecules. The protonation constant (pKa) can be determined based on the equilibrium that indicates the ionization of a compound at a given pH. In this thesis, the protonation constants of clotrimazole, sertaconazole, oxiconazole and climbazole were determined by RP-HPLC method in methanol-water media with mobile phase pH in the range of 3-8. For clotrimazole and klimbazole, in methanol-water medium containing 50%, 55% and 60% (v/v) methanol, for sertaconazole and oxiconazole, in methanol-water medium containing 55%, 57.5% and 60% (v/v) methanol and it was studied at 37°C. Agilent Zorbax SB-CN column (4.6x150mm, 3.5 µm) was chosen for chromatographic analyses. The mobile phase flow rate was fixed at 1ml/min. The wavelength of the compounds was determined as 202 nm. The pKa value of climbazole, clotrimazole, oxiconazole and sertaconazole calculated by using the mole fraction-pKa relationship respectively in water is 6,430; 5,864; 7,114 and 6,901. Likewise, it was calculated as using the 1/Ɛ-pKa relationship, the pKa values of the compounds in water are 6,295; 5,813; 6,813 and 6,806. Within the scope of this thesis, the determined pKa values of these compounds with low water solubility are the necessary data for ionization and ADME properties at different pH values.