2.3 Thermodynamic analysis
The pressure-induced conformational transition from the native state (N) to the intermediate state (I), was determined by examining changes in NMR peak intensities, i.e. peak-area of L109 and V199 methyl groups to estimate an equilibrium constant K (= [I ]/[N ]). Assuming two-state exchange between N and I, the Gibbs free energy difference at any given pressure ΔG p was obtained according to Equation 1. The Gibbs free energy difference ΔG 0 and the partial molar volume difference ΔV 0 between the two conformers at 0.1 MPa was estimated by assuming zero compressibility difference between the states as follows:
\({G}^{p}=-RTln\ K={G}^{0}+{V}^{0}\left(p-p^{0}\right)\) (1)
where R is the gas constant, T is the absolute temperature, p and p 0 are high pressure and 0.1 MPa, respectively.