The protonation and zinc-ion co-ordination equilibria of 2-(polyhydroxyalkyl) thiazolidine-4-carboxylic acid derivatives have been studied by potentiometric titration in the range pH 1.5–8. In most cases the formation of complexes with a metal-to-ligand ratio of 1 : 2 was demonstrated, but at above pH 6 mixed-ligand complexes involving hydroxide-ion co-ordination were also observed. The protonation and complex-formation constants were shown to depend on the structure of the polyhydroxy chains. In the case of the protonation constants this is due to the rearrangement of the intramolecular hydrogen-bonding network, while the complex-formation constants depend on the conformation of the OH groups on the first carbon atoms of the polyol chains.
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K. Burger (1990) studied this question.