Structure of amorphous NaCl–glucose system studied by X-ray diffraction and IR methods

Abstract

X-ray diffraction and diffuse reflection IR spectroscopic measurements have been carried out on amorphous NaCl–glucose mixtures, a-(NaCl) x (glucose) 1− x , with x = 0, 0.05, 0.1 and 0.15, in order to obtain structural information on the intermolecular hydrogen-bonded interaction between glucose molecules affected by the presence of NaCl. The difference distribution function Δ g inter( r) was derived from the Fourier transform of the difference intermolecular interference term Δ i inter( Q) between X-ray intermolecular interference terms observed from amorphous NaCl-glucose and pure glucose samples. A negative peak appears at r ≈ 2.5 Å in the Δ g inter( r) observed for the 10 mol% NaCl sample, while, the Δ g inter( r) for the 15 mol% NaCl sample does not show pronounced negative peak. On the other hand, the IR spectra for the O–H stretching region (2300 ⩽ ν ⩽ 3800 cm −1) indicate that hydrogen bonds between glucose molecules are significantly collapsed in the samples containing 5–15 mol% NaCl. These results imply that the contribution from the Na +⋯Cl − contact ion pair is dominated in the 15 mol% NaCl sample.