Complexes of Amino Acids and Derivatives

1 General Characteristics of Cadmium(II) Complexes of Amino Acids 

Cadmmm(II) complexes of almost aU natural amino acids and numerous amino acid derivatives were studied in the last few decades. The complex formation processes are generally very simple, so in this review the comparison of their stability and structure with those of other metal irais is emphasized. The enhanced stability and high structural variety of the complexes were observed with sulfur-containing amino acids and their derivatives, the characterization of this type of complexes is described in Section 2.3.5. 

The stoichiometry and stability constants of the complexes were determined most frequently by means of potentiometric techniques, but these data were very often completed with results of polarography. The structures of complexes were proposed on the basis of the stoichiometiy and stability of various species and via the analogy to other metal ion complexes. In some cases, the suggested structures of complexes were supported by the use of IR-spectroscopy, Cd NMR, and X-ray studies. 

The stoichiometry and stability constants of cadmium(II)-amino acid complexes are collected in Tables 1 and 2 together with data of the corresponding zinc(II) complexes for comparison. 

These data show that, with the exception of thiol derivatives, exlusively CdL and CdL2 (and CdL3 or CdHL in some cases) complexes are formed in all cadmium(II)-amino acid systems. The stoichiometries of the zinc(II) and cadmium(II) 

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