PROTONATION AND ZINC(II) COORDINATION OF 2-(POLYHYDROXY-ALKYL) THIAZOLIDINE-4-CARBOXYLIC ACID-DERIVATIVES

The protonation and zinc ion coordination equilibria of 2-(polyhydroxyalkyl)thiazolidine-4-carboxylic acid (PHTAC) derivatives have been studied by potentiometric titration in the pH range 1.5-8.5. In most cases the formation of complexes with a metal to ligand ratio of 1:2 was demonstrated, but above pH = 6 mixed-ligand complexes involving hydroxide ion coordination were also observed. The protonation and complex formation constants were shown to depend on the structure of the polyhydroxy chain. 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.