Wrapping Up Hydrophobic Hydration: Locality Matters.

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Biophysics

Background:

• Water's role as a universal solvent is critical in biomolecular processes like folding and recognition.
• Understanding hydrophobic hydration is key to deciphering free energy differences that govern molecular function.
• Solvation entropy's temperature dependence is a crucial factor in molecular interactions.

Purpose of the Study:

• To elucidate the molecular mechanisms behind hydrophobic hydration using computational simulations.
• To differentiate and characterize distinct water populations in the hydration shell of tert-butanol.
• To correlate these water populations with experimentally observed spectral features and thermodynamic properties.

Main Methods:

• Employed ab initio and classical molecular dynamics simulations to model tert-butanol solvation.
• Analyzed hydration water populations, identifying 'HB-wrap' and 'HB-hydration2bulk' states.
• Correlated simulation results with experimental hydration water spectra (164 cm⁻¹ and 195 cm⁻¹ bands).

Main Results:

• Identified two distinct water populations ('HB-wrap' and 'HB-hydration2bulk') in tert-butanol's hydration shell.
• Attributed experimental spectral bands at 164 cm⁻¹ and 195 cm⁻¹ to these specific water populations.
• Established a quantitative link between water coordination motifs and temperature-dependent solvation entropy.

Conclusions:

• The distinct thermodynamic signatures of 'HB-wrap' and 'HB-hydration2bulk' populations explain solvation entropy changes.
• These findings rationalize the observed crossover from entropy to enthalpy dominance in solvation at higher temperatures.
• Provides a molecular basis for understanding hydrophobic hydration effects in biological and chemical systems.