Spectroscopic Fingerprints of Cavity Formation and Solute Insertion as a Measure of Hydration Entropic Loss and Enthalpic Gain
Angew. Chem. Int. Ed.: RESOLV spokeperson Prof. M. Havenith's study addresses the challenge of distinguishing between hydrophilic and hydrophobic contributions to hydration free energies—an essential step toward a deeper understanding of biological processes. By applying THz calorimetry, the team linked specific THz spectral signatures to group-specific solvation entropy and enthalpy. This approach enabled them to separately quantify the contributions of solute-water interactions (hydrophilic effects) and cavity formation (hydrophobic effects) to the overall hydration process.
Dissecting hydration entropy and enthalpy into hydrophobic and hydrophilic contributions from “wrap” and “bound” spectroscopic fingerprints in the low frequency THz range is reported by this study. In the future, this THz-calorimetry decomposition method could be broadly applied to uncover local hydration thermodynamics, e.g. in molecular recognition. Hydration free energies are dictated by a subtle balance of hydrophobic and hydrophilic interactions. Presented by this study is 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. It's shown 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.
