where fi corresponds to the fraction of structural species i in the sample such that the intrinsic property αi represents the degree of hydration of structure i. This model has been successfully applied to describe other systems such as virus dissociation ( Bispo et al., 2012). The considerations related to distinct structures resemble those from the important studies of Monod, Wyman, and Changeux (1965) and Weber (1986) who outlined the initial steps for characterizing heterogeneous species in a two-state or two-structure model.
For the simple case involving only two structural species, i.e., n = 2, Eq. (2) becomes: