Temperature dependence of activation energies for self‐diffusion of water and of alkali ions in aqueous electrolyte solutions. A model for ion selective behavior of biological cells

Samoilov's kinetic hydration model, based on short‐range interactions for aqueous electrolyte solutions, is critically examined. The treatment suffers from a basic assumption that the activation energy for self‐diffusion of ion in water ( E   i (H   2 O) ) is equivalent to the activation energy for self‐diffusion of water from near an ion ( E   H   2 O( i ) ). The change in activation energy for self‐diffusion of water (Δ E ) in the presence of an ion is also obtained under that assumption. A simple approach is outlined, using experimental diffusion data at different temperatures, which shows that ( 1 ) E   i (H   2 O)is not equal to E   H   2 O( i )except at 12°C for Li + , 28°C for Na + , and 44°C for K + , and ( 2 ) Δ E is obtained directly without Samoilov's assumption. The present approach shows that “positive hydrators” and “negative hydrators” interchange their roles along the temperature scale in terms of the sign of Δ E . This property of change in the sign of Δ E with temperature for a given ion may serve as a model to the more complex ion selective behavior of biological cells.