Nature of Bound Water in Colloidal Systems.

The state of water in colloidal systems is a controversial subject. Discovery of the colloidal state by GRAHAM (18) was followed by extensive studies by VAN BEMMELN (66, 67, 68, 69) and ZSIGMONDY (73, 74). Thermodynamic studies by KATZ (36) indicated significant changes in free energy and heat content in colloidal systemis at low water content. OVERTON (51) concluded that part of the water in animal tissue did not have normal solvent properties. The work of ROSA (59) and HOOKER (28) suggested a relationship between certain hydrophilic bio-colloids and cold resistance in plant tissue. NEWTON anid GORTNER (49) proposed a cryoseopic method for the miieasuremiient of hydrophilic colloids as a criterion of the state of water in living and non-living colloid systemiis. The apparently unusual state of water thus disclosed by a vast amount of data has been called "bound" water. It has been assumed that the presenlee of colloidal material was responsible for the observed phenomiienon. It is of particular importance in biologrical systems because of certain iimiplications with regard to hardiness and drought resistance in plants and animals. The majority of investigations have dealt with plant physiology. The estiimiation of bound water is based upon the physical measurement of a variety of properties of water. Some workers compute the amount of bound water from the total change in thermodynamic activity of the water in a given systemii while other workers include only that part of the change in thermiodynamic activity which cannot be accounted for by osmotically active substances. In this paper the calculations are based upon the latter concept and bound water is defined as the amiount of water required to compensate for the deviation of some thermodynamic property of water from the measurement expected in simple solution. It has beeni suggested (17) that bound water is due to the orientation of water molecules about the colloidal particles and that the water, thus removed from the body of the solution, loses its solvent properties. A few investigators have disagreed with these premises. The data of HILL (27) and GROLLMAN (21) did not show appreciable amlounts of bound water in many colloidal systemis. GREENBERG and GREENBERG (20) subjected the concept of lost solvent powers to test and found no evidence for bound water on that basis. A knowledge of the nature of the phenomenon observed is necessary for the interpretation of its role in biological processes.