The interaction of d-galactonic acid with Cr^VI and Cr^III. Structure, stability and physical properties of Cr^III-aldonate complexes

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• 作者：Signorella ; Sandra ; Santoro ; Mabel ; Frutos ; Alejandro ; Escandar ; Graciela ; Salas-Peregrin ; Juan Manuel ; et. al.
• 关键词：Galactonate ; Chromium(III)-aldonate complexes ; Stability ; Structures
• 刊名：Journal of Inorganic Biochemistry
• 出版年：1999
• 出版时间：January 2, 1999
• 年：1999
• 卷：73
• 期：1-2
• 页码：93-100
• 全文大小：594 K

文摘

The redox reaction between d-galactonic acid and potassium chromate yields {((lyxonateH_−1)(galactonateH_−1)Cr(OH₂))K·H₂O}_n, with both aldonate molecules acting as bidentate ligands with the carboxylate and one alkoxo function as the donor sites. The shift of the CO₂^− stretching vibration towards lower frequencies upon coordination and the high value of Δν indicate that the carboxylate acts as a monodentate donor site. Magnetic susceptibility data for the compound in the temperature range 3-300 K exhibit a drop in the effective magnetic moment with temperature below 70 K, which is indicative of antiferromagnetic interactions between the Cr^III centres. The molar magnetic susceptibility versus temperature plot could be fitted with the Fisher Hamiltonian for the case of infinite chains, equation-modified for the presence of monomeric species. The EPR and UV-Vis spectroscopic studies reveal that, in solution, the complex retains the distorted octahedral local coordination geometry. The {((lyxonateH_−1)(galactonateH_−1)Cr(OH₂))K}_n dissociates slowly in aqueous solution but faster at high [H⁺], because of the rapid protonation of the alkoxo bridges linking the monomeric units. The potentiometric evaluation of the closely related binary system Cr^III-d-galactonate shows that the (Cr(galactonateH_−n)₂)^1−2n complexes are the major species in the 4-12 pH range, when a 1:2 Cr^III:ligand ratio is used. ¹³C NMR reveals that the CO₂^− group is one of the coordination sites of the ligand.