TERNARY COMPLEXES OF CADMIUM(II) WITH VITAMIN-D(3) AND AMINO-ACIDS - QUANTITATIVE EXPRESSIONS OF RELATIVE STABILITIES

The formation and stability of ternary complexes of cadmium(II) with vitamin D3 (VD3) and the aminoacids glycine (gly), alanine (ala), histidine (his) and phenylalanine (phe) has been studied by potentiometric pH titrations in 70% (v/v) ethanol-water at 37 +/- 0.1-degrees-C and at 0.10 ionic strength (KNO3). All systems give stable ternary complexes, and DELTA log K values1 are abnormally high (+0.90, +1.08, +0.85, +1.36, respectively). On the contrary, the log X values2 are normal (1.56, 1.59, 1.86, 2.61). The possible reasons that lead to these special results have been discussed in terms of statistical effects and intramolecular ligand-ligand hydrophobic interactions present in the binary and ternary complexes. Some new ideas concerning the stabilities of ternary and the binary complexes have been proposed and discussed.