On the temperature dependence of hydration thermodynamics for noble gases

The hydration thermodynamics of five noble gases in the temperature range 0 -60 degrees C have been carefully determined. We analyse these data using t he theoretical approach developed by Lee that emphasizes that there are dif ferent physical causes for the large and positive hydration Gibbs energy ch ange and the large and positive hydration heat capacity change. The analysi s confirms that the hydrophobicity of noble gases is caused by the excluded volume effect due to solute insertion and exaggerated by the small size of water molecules at any temperature. The reorganization of H-bonds in the h ydration shell of noble gases is a compensating process that does not contr ibute to the Gibbs energy change, but it is the cause of the large and posi tive hydration heat capacity change and determines the temperature dependen ce of the hydration enthalpy and entropy changes. The modified Muller's mod el, despite its simplicity, proves able to satisfactorily describe the reor ganization of H-bonds, indicating that the hydration shell does not resembl e an iceberg. The H-bonds in the hydration shell are energetically slightly stronger but more broken than those in the bulk water.