Isotope effect on solvation Helmholtz energy and structural aspects of aqueous solutions

3 Isotope effect on solvation Helmholtz energy and structural aspects of aqueous solutions 

In the previous section, we derived a general and formal relationship between thermodynamics of solvation and structural changes induced in the water. Now, we present an approximate relationship between the structure of water, 

As in section (7.10.1), we assume in this section that water molecules interact according to a potential function of the form (7.206). We also assume that H20 and D20 have essentially the same pair potential function, except for the HB energy parameter. It is assumed that Hb is slightly larger for D20 than for H20. We denote by D and sH the energy parameters for D20 and H20 respectively. 

Viewing AA W as a function of the HB energy parameter, we expand AA q about AAj 0 to first order in sD-sH and obtain 

The derivative of AA W with respect to sHb may be obtained from the general expression 

---