title: Protonation equilibria of quinolone antibacterials.
abstract: The acid-base properties of seven antibacterial 7-piperazinyl fluoroquinolone derivatives were studied by potentiometry and UV and NMR spectroscopy. These molecules contain two proton-binding sites of similar basicity, namely, the piperazine amino and the carboxylate groups, as proven by 1H NMR spectroscopy. The basicities are quantitated at the molecular level in terms of macroconstants, and also at the submolecular level in terms of microconstants. The microconstants are then used to calculate the concentration of the positive, zwitterionic, neutral, and negatively charged species (microspeciation). The zwitterionic forms always predominate over their neutral protonation isomers, but the zwitterionic:neutral concentration ratio is considerably different for the examined fluoroquinolone derivatives.
authors.affiliation: Institute for Pharmaceutical Chemistry, Semmelweis Medical University, Budapest, Hungary.
authors.forename: K
authors.initials: K
authors.lastname: Takács-Novák
authors.forename: B
authors.initials: B
authors.lastname: Noszál
authors.forename: I
authors.initials: I
authors.lastname: Hermecz
authors.forename: G
authors.initials: G
authors.lastname: Keresztúri
authors.forename: B
authors.initials: B
authors.lastname: Podányi
authors.forename: G
authors.initials: G
authors.lastname: Szász
mesh_terms: D042462:4-Quinolones; D000890:Anti-Infective Agents / Q000737:chemistry*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D008745:Methylation; D011199:Potentiometry; D011522:Protons; D013056:Spectrophotometry, Ultraviolet
chemical_list: D042462:4-Quinolones; D000890:Anti-Infective Agents; D011522:Protons