Complexation of aluminium(III), gallium(III) and indium(III) ions with D-gluconic and lactobionic acids. A potentiometric and nuclear magnetic resonance spectroscopic study

Abstract

The interaction of the trivalent metal ions aluminium(III), gallium(III) and indium(III) with D-gluconic and lactobionic (4-O-β-D-galactopyranosylgluconic) acids has been studied by means of potentiometry and NMR spectroscopy. Potentiometric measurements gave the stoichiometry, species distribution and equilibrium constants of the complexes in aqueous solution at 20.0 °C and /= 0.10 mol dm^–3(NaNO₃). The ¹³C NMR spectroscopic studies revealed line-broadening effects upon complexation, which selectively affected those carbons involved in the complex formation. This enabled the co-ordination sites at both acids to be elucidated. It seems that whereas aluminium(III) prefers to displace the OH protons from the sugar acids even in alkaline media, gallium(III) and indium(III) are able to form hydroxo complexes on increasing the pH.