Effect of stereochemistry on the anti-freeze characteristics of carbohydrates. A thermal study of aqueous monosaccharides at subzero temperatures.

Thermal behavior at subzero temperatures has been investigated for aqueous solutions of various monosaccharides. The heat of fusion of ice measured with differential scanning calorimetry has given linear plots against sugar concentration (wt.%), from which the amount of unfrozen water, Uw, has been determined for each monosaccharide. The results for Uw are analyzed by employing, as a measure of hydration characteristics, known physico-chemical properties of aqueous monosaccharides, such as partial molar compressibilities, etc. It was revealed that the anti-freeze characteristics of carbohydrates depend on their stereochemistry. More water remains unfrozen in the aqueous solutions of carbohydrates having poorer compatibility with the three-dimensional hydrogen-bond network of water. Monosaccharides studied can be subdivided into three groups according to the extent of the anti-freeze effect. These results are rationalized in terms of a modified stereospecific hydration model.