COMPARISON OF THE POLAROGRAPHIC-BEHAVIOR OF THE CD-2+-GLYCINE, N-ACETYL-GLYCINE AND N-BENZOYL-GLYCINE SYSTEMS IN AQUEOUS AND ETHANOLIC SOLUTION

The complexation reactions of glycine, N-acetyl- and N-benzoyl-glycine with the Cd2+ ion were studied as a model for metal-protein interactions, using polarographic techniques in aqueous and ethanolic solution at 0.1 M NaclO4, as base electrolyte, to identify the number and type of solution complex species and to calculate their stability constants. In aqueous solution three complexes of the forms CdL+, CdL2 and CdL-3 coexist in the pH range 7-10 for the glycine, while the N-protected amino acids do not react under any pH conditions. In ethanolic solution four complexes of the forms CdL+, CdL2, CdL-3 and CdL2-4 coexist for the N-protected amino acids, while for the glycine the CdL2-4 complex prevails. A Hammett relationship is observed between the reversible E 1 2 of β4 (stability constant)values versus the σ constants for the substituents on the amino group. A coordinative hypothesis for the complexes in solution is also suggested. © 1979.