Configuration-dependent complex formation between Ca(II) and sugar carboxylate ligands in alkaline medium: Comparison of L-gulonate with D-gluconate and D-heptaguconate

• Published in: Carbohydrate research Vol. 460; pp. 34 - 40
• Main Authors: Kutus, Bence, Dudás, Csilla, Peintler, Gábor, Pálinkó, István, Sipos, Pál
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Ltd 02.05.2018
• Subjects: Calcium; Calcium - chemistry; Carboxylic Acids - chemistry; Complexation; Configuration-dependence; D-gluconate; D-heptagluconate; Gluconates - chemistry; L-gulonate; Magnetic Resonance Spectroscopy; Sugar Acids - chemistry; Sugars - chemistry; Water - chemistry; D-heptagluconate; Complexation; L-gulonate; Calcium; D-gluconate; Configuration-dependence
• ISSN: 0008-6215; 1873-426X
• DOI: 10.1016/j.carres.2018.01.012

The calcium sugar carboxylate interactions in hyperalkaline solutions are of relevance in radioactive waste repositories and in certain industrial processes. The complex formation between L-gulonate and Ca2+ ions was studied in strongly alkaline medium at 25 °C and 1 M ionic strength and was compared with previous results reported for D-gluconate and D-heptagluconate. The deprotonation of the ligand was confirmed by potentiometric and 13C NMR spectroscopic measurements. Pronounced pH effects were seen in the presence of Ca2+ indicating strong complex formation. By the evaluation of the experimental data, two highly stable trinuclear species, Ca3Gul2H–3+ and the Ca3Gul2H–40, are formed in alkaline aqueous solutions. Polarimetric as well as 1H NMR spectroscopic measurements attested that the increased complex stability was due to the formation of strong metal ion - alcoholate interactions. Moreover, the 1H NMR spectra of the three anions refer to the role of configuration in metal ion-binding. That is, the participation of the C3-OH or C4-OH group is governed by the relative position (i.e., threo or erythro) of the C2-OH and C3-OH groups. [Display omitted] •L-gulonate forms remarkably stable complexes with Ca2+ in strongly alkaline aqueous solutions.•Two trinuclear species, Ca3Gul2H–3+ and Ca3Gul2H–40, were found to be formed via binding through the alcoholate groups.•The structure and stability of these multinuclear complexes were compared with those of D-gluconate and D-heptagluconate.•The structure of these complexes was found to be configuration dependent.•The coordination of the C3-OH or C4-OH group was found to be governed by the relative position of the C2-OH and C3-OH groups.