Spectroscopic Fingerprints of Cavity Formation and Solute Insertion as a Measure of Hydration Entropic Loss and Enthalpic Gain
Simone Pezzotti, Federico Sebastiani, Eliane P. van Dam, Sashary Ramos, Valeria Conti Nibali, Gerhard Schwaab, Martina Havenith
Abstract
Abstract Hydration free energies are dictated by a subtle balance of hydrophobic and hydrophilic interactions. We present here a spectroscopic approach, which gives direct access to the two main contributions: Using THz‐spectroscopy to probe the frequency range of the intermolecular stretch (150–200 cm −1 ) and the hindered rotations (450–600 cm −1 ), the local contributions due to cavity formation and hydrophilic interactions can be traced back. We show that via THz calorimetry these fingerprints can be correlated 1 : 1 with the group specific solvation entropy and enthalpy. This allows to deduce separately the hydrophobic (i.e. cavity formation) and hydrophilic contributions to thermodynamics, as shown for hydrated alcohols as a case study. Accompanying molecular dynamics simulations quantitatively support our experimental results. In the future our approach will allow to dissect hydration contributions in inhomogeneous mixtures and under non‐equilibrium conditions.