Investigating the Water State in Saccharide Solutions by Infrared/Far-Infrared Spectra in the 1000-100 cm-1 Region Combined with Bands in the 4000-3000 cm-1 Region.

Abstract

Water molecules are arranged as tetrahedral structures, owing to the hydrogen-bonding network in solution. However, many aspects of their actual state remain unclear. This study analyzed saccharide solutions of various concentrations by infrared/far-infrared (IR/FIR) spectra in the 1000-100 cm^-1 region and IR spectra in the 4000-3000 cm^-1 region. The relationship between the second-derivative intensities of bands at 3210 and 3374 cm^-1 attributed to strong and weak hydrogen bonds, for glucose, maltose, sucrose, and NaCl solutions at different concentrations, was described by the same straight line. Two bands were also extracted from the IR/FIR region, which are attributed to the ordered and distorted structures of the water. The ratio indices A_high/A_low and A₃₂₁₀/A₃₃₇₄ were developed using the intensities of the bands at 673 and 403 cm^-1 and at 3210 and 3374 cm^-1, respectively. Both indices increased with the saccharide concentration. The results show that saccharide molecules contributed to the strengthening of the water structure. Moreover, the change in A_high/A_low was small compared to that in A₃₂₁₀/A₃₃₇₄ at high saccharide concentrations. Therefore, a difference in the state of water possibly exists between those expressed by IR and IR/FIR spectra, and the complementary use of these spectra is effective in clarifying the state of water in solution.