 Equilibrium unfolding is used to determine the conformational stability of the molecule.In its simplest form, equilibrium unfolding assumes that the molecule may belong to only two thermodynamic states, the "folded state" (typically denoted "N" for "native" state) and the unfolded state (typically denoted "U").This "all-or-none" model of protein folding was first proposed by Tim Anson in 1945, but is believed to hold only for small, single structural domains of proteins (Jackson, 1998); larger domains and multi-domain proteins often exhibit intermediate states.