Figure 7. Thermodynamic cycle for separating the contributions of hydration of native (V_Hyd,N) and unfolded (V_Hyd,U) state ensembles from the contribution of geometric volume changes (ΔV_SE) to the total changes in volume (ΔV_Tot) upon protein unfolding in aqueous solution.

The sum of all three steps is equal to the volume of unfolding of the protein in aqueous solution, ΔV_Tot, as defined by equation (11). It must emphasized that this process is valid because volume as a thermodynamic parameter is a state function and there are no conformational changes in the native or unfolded state ensembles upon transfer to and from the gas phase.