Thermodynamic considerations in co-ordination. Part XIV. Formation constants for lead(II)–amino-acid complexes and their use in computing the complexing competition between lead(II) and in vivo essential metal ions, and in computer evaluation of ligands currently employed as lead(II) chelating therapeuticals

Abstract

Potentiometrically determined formation constants are reported for the lead(II) asparaginate, aspartate, cysteinate, glutaminate, histidinate, phenylalanate, serinate, and tryptophanate systems at 25°, I= 3·00M(Na⁺)ClO₄^–. Computer simulated models of blood plasma conditions were used to examine (a) the complexing competition between lead(II) and manganese(II), iron(II), cobalt(II), copper(II), and zinc(II)–amino-acid anion complexes, and (b) to assess the selectivities of EDTA and D-penicillamine for lead(II) and the in vivo essential amino-acids listed. The more important conclusions under (a) were that the lead(II) complexes the cysteinate ligand at the expense of the zinc(II)–cysteinste system and then produces increased concentrations of other zinc complexes, and under (b) that more specific drugs may be synthesized as peptides derived from L-cysteine, histidine, and aspartic acid.