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Abstract
The effective overall stability constants (log Ke values) and molar combining ratios for nine aliphatic aminocarboxylic acids (C2 to c6) with copper (II) ion were calculated from spectrophotometric and potentiometric data at pH 3.0, 4.0 and 5.0 and 25°C. In addition, calculated overall stability constants (log Kn values), using Bjerrum's method of analyzing potentiometric data, showed that chelates of alpha- and beta-aminocarboxylic acids with copper (II) were more stable than those of gamma-and epsilon-aminocarboxylic acids. Using Job's method of continuous variations for analyzing absorbance data, it was observed that while the alpha- and beta-aminocarboxylic acids formed both bicoordinated (1:1) and tetracoordinated (2:1) chelates with copper (II) ion at pH 4:O and 5:O and the alpha-aminocarboxylic acids formed only a (1:1) chelate at pH 3.0, the gamma and epsilon-aminocarboxylic acids showed only bicoordinated (1:1) chelate formation at pH 5.0.
The complexation of epsilon-aminocarboxylic acid ligand to copper (II) ions appears to be through both the amino and the carboxylate groups rather than through carboxylate ion, alone as previously suggested by other workers. The implication of this finding is that the formation of chelate ring structures greater than eight members is a distinct possibility in the aliphatic aminocarboxylic acid series and further suggests the opportunity for more complex metallobinding in proteins as well.