13C NMR study of the complex formation of sorbitol (glucitol) with multivalent cations in aqueous solution using lanthanide(III) nitrates as shift reagents

Complexation of sorbitol (glucitol) in aqueous solutions with the lanthanide ions LaIII, PrIII, EuIII and YbIII, as model systems for the complexation with the isosteric CaII, was studied by 13C NMR spectroscopy. Ytterbium(III) nitrate proved to be the reagent of choice, in effectiveness and in linearity vs concentration of the induced upfield shift. Tridentate complexation of YbIII with O‐2, O‐3 and O‐4 was established and the conformation of the sorbitol‐YbIII complex in water was found to be the same as that of the sorbitol‐PrIII complex, as inferred from 1H NMR spectra. Off‐resonance decoupling and the isotope effects observed in sorbitol‐1‐d and sorbitol‐5‐d, allowed the complete, reliable assignment of the 13C NMR spectrum of sorbitol. Assignments in the literature proved to be incorrect.