Sucrose Hydrates in Aqueous Solution by IR Spectroscopy

Two sucrose hydrates were found by factor analysis (FA) of the mid-infrared attenuated total reflectance (MIR-ATR) spectra of a series of aqueous sucrose solutions: sucrose penta- and dihydrate. The spectra of the isolated hydrates and their abundances as a function of concentration were obtained. Apart from the intensity of the water bands, the two hydrates differ only in a few sucrose bands in the C−O region. From the distribution of the species, the equilibrium between penta- and dihydrate was deduced: 3H 2 O + C 12 H 22 O 11 ·2H 2 O ⇌ C 12 H 22 O 11 ·5H 2 O. The pentahydrate equilibrium constant was found to be K e = (4.1 ± 0.3) × 10 -5 L 3 mol -3 . The two hydrates observed in aqueous solution are not found in the solid state. Analysis of the integrated intensity of the OH stretching band of sucrose−H 2 O mixtures shows that the OH vibrations in both the sucrose and the associated water are modified in the mixtures, indicating strong intermolecular interactions that influence the band intensities.