Dynamical structure of water in aqueous solutions of D-glucose and D-galactose by low-frequency Raman scattering

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Abstract
Low‐frequency depolarized Raman spectra of aqueous solutions of D‐glucose and D‐galactose have been investigated in the frequency region from −250 cm−1 to 250 cm−1 at 30.0 °C as a function of concentration up to 0.04 molar ratio. The dynamical structure of water in aqueous solution is analyzed by using the reduced Raman spectrum χ‘(ν̄), which corresponds to the imaginary part of the dynamical susceptibility. The reduced spectrum is fitted with the superposition of one Cole–Cole type relaxation mode and two damped harmonic oscillator modes by a nonlinear least‐squares fitting. The effects of D‐glucose and D‐galactose on the dynamical structure of water in aqueous solution are similar. The relaxation time of hydrogen bond among water molecules becomes slower with increasing sugar concentration. The characteristic frequencies of stretching‐like and bending‐like vibrations among water molecules do not change in both D‐glucose and D‐galactose aqueous solutions.