IONIZATION AND SOLUBILITY OF AN AMPHOTERIC BETA-LACTAM ANTIBIOTIC

Solution equilibria of an experimental antibiotic (code named CP-38,371) were investigated. In the pH range 2-4 the compound has 2 pK values. These overlapping macroconstants were determined by 3 methods: potentiometric titration, spectrometric titration and curve-fitting of pH-solubility data. Potentiometric values of pK1 = 2.86 and pK2 = 3.81 at 25.degree. C (.mu. = 0.2) aggreed (.+-. 0.1 unit) with the constants determined by the other methods. CP-38,371 is amphoteric and pK3 = 7.50 was determined by potentiometric and solubility methods. The complete microionization scheme for the compound was simplified by consideration of the UV spectral characteristics of the ionizing groups. Using absorbance-pH data, 4 microconstants for the important processes were calculated by the method of Edsall et al., and by a method developed by the authors. The 2 procedures gave identical results.