Ultrasonic and densimetric characterizations of the hydration properties of polar groups in monosaccharides

The partial molar volumes and adiabatic compressibilities for 14 monosaccharides in aqueous solution at the temperatures of 18, 25, 40, and 55 degrees C are reported. These experimental data allow estimation of the solvent contraction, V-I, caused by the polar groups of monosaccharides with four, five, and six polar groups. On average, each polar group in pentoses causes a 15-20% stronger contraction of water than a polar group in 2-deoxyribose, while each polar group in hexoses causes a 5-10% stronger contraction of water than a polar group in 2-deoxyhexoses and 6-deoxyhexoses. In addition, polar groups of 2-deoxyribose, 2-deoxyglucose, and 2-deoxygalactose exhibit essentially higher (less negative) compressibility contributions relative to polar groups of pentoses, 6-deoxyhexoses, and hexoses. The volume and compressibility data reported in this paper suggest similar hydration of the polar groups of pentoses and hexoses. Furthermore, the data suggest that, in monosaccharides, the hydroxyl group in the 2-position plays a crucial role in "switching on" the cooperative amplification of solute hydration (perhaps, via the formation of water networks). Removal of this group brings about a dramatic decrease in solute hydration with a concomitant increase in the compressibility contribution per polar group. Consequently, 2-deoxyribose and 2-deoxyhexoses manifest significantly weaker hydration compared to pentoses, 6-deoxyhexoses, and hexoses.