Degradation kinetics of a new cephalosporin derivative in aqueous solution.
The degradation kinetics of a new cephalosporin derivative (1) in aqueous solution were investigated at 60 degrees, mu = 0.05, at pH 2.0-10.0. The observed degradation rates followed pseudo-first-order kinetics and were influenced significantly by H2O and OH- catalysis. No primary salt effect was observed in the acid region, but a positive salt effect was observed at pH 9.4. A general base catalytic effect by a phosphate buffer species was observed at pH 7-8. The pH-rate profile for I exhibited a degradation minimum at pH 6.05. The Arrhenius activation energies determined at pH 4.0 and 9.4 were 27.2 and 24.5 kcal/mole, respectively. Excellent agreement between the theoretical pH-rate profile and the experimental data supported the hypothesized degradation process. A comparison of I and cefazolin revealed close structural and stability analogies.
D002021:Buffers; D002384:Catalysis; D002437:Cefazolin / Q000031:analogs & derivatives*; D002626:Chemistry, Pharmaceutical; D004355:Drug Stability; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008823:Micelles; D013696:Temperature
D002021:Buffers; D008823:Micelles; D002437:Cefazolin