[Study of E. coli penicillin amidase. The pH dependence of the equilibrium constant of ampicillin enzymatic hydrolysis]. / Izuchenie penitsillinamidazy iz E. coli. pH-zavisiomst' konstanty ravnovesiia fermentativnogo gidroliza ampitsillina.

The equilibrium parameters of the hydrolysis of ampicillin catalysed by penicillin amidase were determined within the pH range of 4.5 to 5.5. The values of the ionization constants of the carboxy group of D-(-)-ALPHA-AMINOPHENYLACETIC ACID (PK1=1.80) and amino group of 6-aminopenicillanic acid (pK2=4.60) were estimated and pH-dependence of the effective free energy of ampicillin hydrolysis was calculated. It was shown that the thermodynamic optimum of ampicillin synthesis was at 3.20 (the value of the effective free energy under the experimental conditions was 3.27 kcal/mole). The value of the "true", pH-independent free energy of hydrolysis (deltasigma) of the amide bond in the ampicillin molecule was determined to be equal to 9.72 kcal/mole. The thermodynamic parameters of ampicillin and benzylpenicillin hydrolysis were compared. The amino group in the alpha-position of phenylacetic acid was shown to have a significant effect on the values of "true" free energy of hydrolysis of the penicillin amide bond and free ionization energy in the system.

[Physico-chemical properties of 7-aminodesacetoxycephalosporanic acid]. / Fiziko-khimicheskie svoistva 7-aminodezatsetoksitsefalosporanovoi kisloty

7-Aminodesacetoxycephalosporanic acid (7-ADCA) of 99 per cent purity was prepared by enzymatic hydrolysis of 7-phenylacetamidodesacetoxycephalosporanic acid. Its isoelecti point was determined by the electrophoretic method. Potentiometric titration of zwitterion of 7-ADCA was performed and the constants of its ionization were calculated. Minimum solubility of 7-ADCA zwitterion was determined and the curve of 7-ADCA solubility at wide pH ranges was estimated. Equilibrium of 3 forms of 7-ADCA was estimated.

[Physicochemical properties of 7-phenylacetamidodesacetoxy-cephalosporanic acid]. / Fiziko-khimicheskie svoistva 7-fenilatsetamidodezatsetoksi-tsefalosporanovoi kisloty

7-phenylacetamidodesacetoxycephalosporanic acid was prepared by transformation of benzylpenicillin. The acid was subjected to potentiometric titration and investigation of its electrophoretic mobility at wide pH ranges. The data of the potentiometric titration and electrophoresis were used for calculation of the acid ionization constant. Minimum solubility of the acid was determined and the curve of its solubility at wide pH ranges was estimated.