ΔGH2O and mGdHCl values obtained for staphylococcal nucleases at room temperature ~25°C using the PEPS HX ESI-MS method compared to fluorescence values [5, 6,36]. Units of ΔGH2O and mGdHCl units are kcal mol− and kcal mol−1 M−1 respectively. Estimated average uncertainty for the ΔGH2O is ~0.3 kcal/mol and for mGdHCl it is 0.1 kcal mol−1 M−1.