Static water structure detected by heat capacity measurements on aqueous solutions of a triple-helical polysaccharide schizophyllan

摘要

Heat capacity measurements were made on aqueous solutions of a triple-helical polysaccharide schizophyllan by precision adiabatic calorimetry over a wide range of concentrations 30-45-90.93 wt% temperatures between 5 and 315 K.The heat capacity curves obtained were divided into four groups depending on the weight fraction of schizophyllan w regions I-IV.In region I,triple-helices with the sheath of bound water,structured water,and loosely structured water forming layers around the helix core are embedded in free water.In region II,there is not free water,and loosely structured water decrease until it vanishes,but structured water stays constant with increasing w.In region III,bound water remains unaffected,but structured water decreases with increasing w by overlapping each other.Finally,in region IV,only schizophyllan and bound water exist,the latter decreasing upon increasing w.The maximum thickness of each layer is 0.18_3 nm for bound water,0.13_4 nm for structured water,and 0.23_6 nm for loosely structured water,and these layers of water are at the enthalpy levels of 53%,93.7%,and nearly 100%,respectively,between ice (0%) and free water (100%).