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 sucr ose solutions: sucrose penta- and dihydrate. The spectra of the isolated hy drates and their abundances as a function of concentration were obtained. A part 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 specie s, the equilibrium between penta- and dihydrate was deduced: 3H(2)O + C12H2 2O11. 2H(2)O reversible arrow C12H22O11. 5H(2)O. The pentahydrate equilibri um constant was found to be K-e = (4.1 +/- 0.3) x 10(-5) L-3 mol(-3). The t wo 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 2O mixtures shows that the OH vibrations in both the sucrose and the associ ated water are modified in the mixtures, indicating strong intermolecular i nteractions that influence the band intensities.