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Effect of copper (II)--glycine chelates on degradation of penicillin in mildly acid solution.

This study was undertaken to elucidate by in vitro kinetic analysis the role that Cu (II) ions, through complexation with an amino acid, may have in the degradation of the penicillins and the formation of the penicilloyl determinant. The data obtained indicated that in the presence of the Cu (II)-glycine chelates, penicillin is quantitatively hydrolyzed to penicilloic acid. This finding is in direct contrast to the much slower reaction between penicillin and glycine in the absence of Cu (II), in which the major degradation product is the penicilloamide. The overall observed rate constant can be represented by: k0 = Km[M][OH−] + Kmg [MG][OH−] in which Km and Kmg are the catalytic coefficients for Cu (II) and the 1:1 Cu (II)-glycine chelate, respectively, and [M] and [MG] represent the concentrations of free Cu (II) and the 1:1 chelate, respectively. The postulated mechanism involves the rapid formation of a ternary penicillin-Cu (II)-glycine complex, followed by a rate-limiting hydroxyl-ion attack.