SUGAR INTERACTION WITH ALKALI METAL IONS. SYNTHESIS AND VIBRATIONAL SPECTRA OF CRYSTALLINE SUCROSE AND ITS SODIUM HALIDE ADDUCTS

Abstract

Sucrose interacts with NaCl. NaBr and NaI to give adducts of the type Na(sucrose)Cl·2H₂O Na(sucrose)Br·2H ₂O and Na ₃(sucrose) ₂I₃·3H₂O. A comparison between the infrared spectra of free sucrose and its metal adducts has been made and a correlation between spectral changes and the binding sites used by the sugar molecule has been established. X-ray structural information shows that the Na⁻ ion is six-coordinated in the structurally identified compound Na(sucrose)Br·2H₂O and its isomorphous analogue Na(sucrose)Cl·2H₂O, but differs from this in the Na₃(sucrose)₂I₃·3H₂O compound. The sodium ion binds through 0(4), 0(6), 0(6′) of the sugar and to two water molecules as well as to a halide anion, resulting a six-coordinated metal ion based on a distorted octahedron geometry. The strong sugar hydrogen bonding network is rearranged upon sugar metallation and the assignments of the absorption bands in the OH stretching region of the spectra have been made based on the X-ray structural analysis and neutron diffraction measurements.