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Multinuclear complex formation in aqueous solutions of Ca(II) and heptagluconate ions
Attila Pallagi1, Zita Csendes, Bence Kutus
1Department of Inorganic and Analytical Chemistry, University of Szeged, Dóm tér 7, Szeged, H-6720 Hungary.
Abstract:
The equilibria and structure of complexes formed between the Ca(2+) ion and the heptagluconate (Hglu(-)) ion in both neutral and alkaline solutions have been studied. In alkaline solutions an uncharged, multinuclear complex is formed with the composition of Ca3Hglu2(OH)4 (or [Ca3Hglu2H(-4)](0)) with an unexpectedly high stability constant (lg β(32-4) = 14.09). The formation of the trinuclear complex was deduced from potentiometry and confirmed by freezing-point depression measurements and conductometry as well. The binding sites of Hglu(-) were determined from NMR measurements. Besides the carboxylate group, the O atoms on the second and third carbon atoms proved to be the most probable sites for Ca(2+) binding.
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