Sugar adducts with alkaline earth metal ions. Interaction of L-arabinose with Sr(II) and Ba(II) ions and the effects of metal ion binding on the sugar anomeric configurations.

The reaction between L-arabinose and hydrated Sr(II) or Ba(II) halide salts has been studied in H2O solution and adducts of the type M(L-arabinose)X(2).4H(2)O, where M = Sr(II) or Ba(II) and X = Cl- or Br- have been isolated and characterized by means of Fourier transform infrared spectroscopy, 1H-NMR spectroscopy, molar conductivity and X-ray powder diffraction measurements. Due to the marked spectral similarities with those of the structurally known Ca(L-arabinose)X2 . 4H2O (X= Cl- or Br-) compounds, the Sr(II) and the BA(II) ions are eight-coordinated, binding to two l-arabinose molecules via O1, O5 of the first and O3, O4 of the second sugar moiety and to four H2O molecules. 1H-NMR spectroscopy indicated that the free L-arabinose has the beta-anomer configuration in aqueous solution, whereas the alpha-anomer isomer is preferred by Mg(II), Ca(II), Sr(II) and Ba(II) ions, on complexation.