Preferential solvation of dextran in water-ethanol mixtures

Abstract

The amount of water bound on dextran in water-ethanol mixtures was determined by measuring the adiabatic compressibility of dextran samples of molecular weight above 104. Similar measurements were also carried out on glucose, maltose, and raffinose, and the results were compared with those of dextran. The partial specific compressibility (κ2-0) of these saccharides increases with increasing ethanol concentration in solvent and takes a constant value above about 20 wt% of ethanol. The interpretation for this is that the water molecules bound to solute are removed by ethanol; thus, dextran is hydrated preferentially in water-ethanol mixtures. The viscosity of dextran solutions was measured as a function of ethanol concentration and the molecular weight of the dextran samples. From the values of κ2-0 at concentrations of ethanol above about 20 wt%, the compressibility of dextran in solution was estimated to be about 4.0×10-11 Pa-1. This value was compared with the elastic moduli of glucose, maltose, and dextran, estimated from their bond-stretching and -bending force constant. © 1982, The Society of Polymer Science, Japan. All rights reserved.