Protonation equilibrium and lipophilicity of moxifloxacin.

This study was performed to characterise the protonation equilibrium at the molecular level and pH-dependent lipophilicity of moxifloxacin. After determining macro- and micro-constants, distribution features of four microspecies in aqueous phase were assessed. The apparent partition coefficient versus pH profile of moxifloxacin showed a parabolic curve in n-octanol/buffer system which reached near pI. The true partition coefficient was calculated from the log P(app) and microconstants values.