Multinuclear complex formation between Ca(II) and gluconate ions in hyperalkaline solutions.

Alkaline solutions containing polyhydroxy carboxylates and Ca(II) are typical in cementitious radioactive waste repositories. Gluconate (Gluc(-)) is a structural and functional representative of these sugar carboxylates. In the current study, the structure and equilibria of complexes forming in such strongly alkaline solutions containing Ca(2+) and gluconate have been studied.

Complexation of Al(III) with gluconate in alkaline to hyperalkaline solutions: formation, stability and structure.

Contrary to suggestions in the literature, it has been proven that Al(III) forms a 1 : 1 complex with gluconate (hereafter Gluc(-)) in strongly alkaline (pH > 12) aqueous solutions. The complex formation was proven via(27)Al and (1)H NMR, freezing-point depression, polarimetric measurements as well as potentiometric and conductometric titrations. This complexation is a pH independent process, i.

Multinuclear complex formation in aqueous solutions of Ca(II) and heptagluconate ions.

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).

Multinuclear NMR and molecular modelling investigations on the structure and equilibria of complexes that form in aqueous solutions of Ca(2+) and gluconate.

Complexation of d-gluconate (Gluc(-)) with Ca(2+) has been investigated via (1)H, (13)C and (43)Ca NMR spectroscopy in aqueous solutions in the presence of high concentration background electrolytes (1MI4M (NaCl) ionic strength). From the ionic strength dependence of its formation constant, the stability constant at 6pH11 and at I-->0M has been derived (logK(1,1)(0)=1.8+/-0.