*4.6. Fraction Folded Population and Folding Free Energy (*∆*Gfold)*

The equilibrium constant between the unfolded and folded states of an experimental peptide is the ratio of the folded and unfolded populations. The fraction folded population for each residue was derived from the chemical shift data according to Equation (5). The folding free energy ∆Gfold for each residue was derived using Equation (6). The fraction folded population and folding free energy (∆Gfold) of the peptide was obtained by averaging the fraction folded population and ∆Gfold, respectively, for the residues 2, 3, 9, and 10 [11,20,22,23].

$$\text{Fraction Folded Population} = \frac{\ $\text{H}\alpha(\text{exp}) - \$ \text{H}\alpha(\text{U})}{\ $\text{H}\alpha(\text{F}) - \$ \text{H}\alpha(\text{U})} \times 100\% \tag{5}$$

$$\Delta\mathbf{G}\_{\text{fold}} = -\text{RTln}\frac{\delta\mathbf{H}\alpha(\exp) - \delta\mathbf{H}\alpha(\mathbf{U})}{\delta\mathbf{H}\alpha(\mathbf{F}) - \delta\mathbf{H}\alpha(\exp)}\tag{6}$$
