Evaluation of the binding constants, bound chemical shifts, and equilibrium stoichiometry for the association of lanthanide shift reagents with carbohydrate derivatives

The molecular associations of tris(dipivalomethanato)europium(III) (1) and of tris(2,2-dimethyl-6,6,7,7,8,8,8,-heptafluoro-3,5-octanedionato)europium(III) (2) with six carbohydrate derivatives have been studied. The interactions of 2 in deuterochloroform solution appear to be "normal", i.e., the plot of [sugar concentration] versus [induced chemical-shift change]^-1 is linear and can be interpreted in terms of the equilibrium binding constant (K_B) and the bound chemical shifts (°_B). Similar results are found for 1 in carbon tetrachloride solutions. However, in chloroform solutions, non-linear plots are obtained that cannot be simply interpreted. Possible reasons for this behaviour are given.