Interactions of calcium nitrate with pyranosides in water: A 13C NMR study

The 13C NMR spectra of methyl α- and β-d-galactopyranosides, and methyl α- and β-d-glucopyranosides were recorded and show that the Δ(δC-4) values for methyl α- and β-d-galactopyranosides increase most rapidly, whereas those for methyl α- and β-d-glucopyranosides vary hardly with increasing molality of calcium nitrate. It can be concluded that ax-OH-4 interacts more strongly with Ca2+ than eq-OH-4 group, namely, the Ca2+ ion interaction with ax-OH-4 leads to a stronger deshielding of the C-4 atom. Compared with other C atoms, the chemical shifts of both C-1 and C-5 atoms in these two types of glycosides decrease relatively rapidly as molality of calcium nitrate increases, indicating that the nitrate ion attractions for these glycosides cause a relatively strong enhancing shielding effect of C-1 and C-5 atoms.