RESUMO
Cadmium (II) ion-catalyzed degradation of ampicillin in methanol at 20 degrees C has been studied. It has been observed that the rate values tend to saturate when the concentration of ampicillin or the metal ion is increased. The results obtained in the present study suggest that ampicillin degradation occurs through the formation of a 1:1 (SM) and 2:1 (S(2)M) ampicillin-metal complexes. These complexes decompose giving a single product (absorption maximum at 285 nm; ((p)=1.82x10(4) l mol(-1) cm(-1)) that has been isolated and identified (Cd(II) (L(2-))(2) (H(2)O)(4) Na(2)). The appearance of this product reflects a first order reaction with respect to the 1:1 complex, with a rate constant of 3.87x10(-2) min(-1) and the existence of an equilibrium between the 1:1 and 2:1 initial complexes. The equilibrium constant value, calculated from kinetic data, is 1.7x10(3) l mol(-1).
RESUMO
The present article considers several physicochemical aspects of the complexation reaction of sodium amoxicillin and Cu(II) ion in a methanolic medium. Analysis of spectrophotometric data demonstrated the formation of two complex species with amoxicillin:Cu(II) ion mole ratios of 1:1 and 2:1. Stability constants (beta) and molar absorptivities at 610 nm (epsilon) of the complexes (20 degrees C) in methanol were calculated simultaneously by a computer program on the basis of absorbance data obtained at 610 nm. The values thus calculated for the 1:1 complex were as follows: log beta 1 = 5.48 +/- 0.21 L.mol-1, epsilon 1 = 70 +/- 2 L.mol-1.cm-1. The values for the 2:1 complex were as follows: log beta 2 = 8.98 +/- 0.17 L2.mol-2 and epsilon 2 = 138 +/- 4 L.mol-1.cm-1. The amoxicillin:Cu(II) ion complexes were quite stable over time.
