Supercooled carbohydrates

L. Poppe and H. van Halbeek, NMR spectroscopy of hydroxyl protons in supercooled carbohydrates, Nature Struct. Biol., 1 (1994) 215—216. 

Ludwig s (2001) review discusses water clusters and water cluster models. One of the water clusters discussed by Ludwig is the icosahedral cluster developed by Chaplin (1999). A fluctuating network of water molecules, with local icosahedral symmetry, was proposed by Chaplin (1999) it contains, when complete, 280 fully hydrogen-bonded water molecules. This structure allows explanation of a number of the anomalous properties of water, including its temperature-density and pressure-viscosity behaviors, the radial distribution pattern, the change in water properties on supercooling, and the solvation properties of ions, hydrophobic molecules, carbohydrates, and macromolecules (Chaplin, 1999, 2001, 2004). 

Understanding and predicting water diffusivity in supercooled and glassy carbohydrates is of great importance in the practical applications of these mixtures, in particular to the preservation of foods and pharmaceuticals. Since the discovery more than a decade ago that water retained liquid-like heat capacity in glassy starch (Noel and Ring, 1992) several studies have shown that water is mobile in glasses of carbohydrates (van den Dries et al., 1998 van den Dries et al., 2000 Tromp et al., 1997 Hills et al., 2001 Chatakanonda et al., 2003 Kou et al., 2000 Vodovotz et al., 2000 Aldous et al., 1997) and foods (Roudaut et al., 1999). 

We present here coarse grain simulation results of two simple binary water-carbohydrate mixtures that shed light on the mechanism of water diffusion in the supercooled and glassy state, the coupling of water mobility in the glass to the sub-Tg dynamics of the matrix, and the effect of the internal modes of the saccharide on the decoupling of water motion from carbohydrate translation. 

Finally, we examine the effect of the timescale of the local degrees of freedom of the carbohydrate on the d)mamics of water by comparing the mechanism of water diffusion in the solutions of the supercooled monomer DPI and the oligomer DP12. We have studied the two mixtures of identical... 

---