Ca2+-Assisted DOSY NMR: An Unexpected Tool for Anomeric Identification for D-Glucopyranose

D-glucopyranose undergoes mutarotation into a mixture of anomers, alpha- and beta-D-glucopyranose, once it is dissolved in an aqueous solution. Distinguishing the two anomers by routine NMR methods are difficult because of their similarity and hence overlapped H-1-NMR spectra. In this paper, we demonstrate that the DOSY technique can be used to discern the two anomers of the D-glucopyranose. This is possible when taking advantage of a matrix effect of Ca2+, which separate the alpha- and beta-anomers of D-glucopyranose by their differences in diffusion. The effect of Ca2+ was further supported by DFT calculations. Our results demonstrate the power of DOSY NMR to gain a deeper understanding of the interactions between carbohydrates and metal ions.