Hydration interactions beyond the first solvation shell in aqueous phenolate solution.

Area of Science:

• Physical Chemistry
• Chemical Physics
• Computational Chemistry

Background:

• Understanding the solvation dynamics of ions is crucial for various chemical and biological processes.
• The role of specific molecular interactions, like hydrogen bonding, in structuring solvent shells around solutes is a key area of research.

Purpose of the Study:

• To investigate the orientational dynamics of water molecules around phenolate ions.
• To compare the solvation behavior of phenolate with neutral phenol to elucidate the effect of charge.
• To understand the influence of the anion's hydrophilic and hydrophobic parts on water molecule immobilization.

Main Methods:

• Ultrafast vibrational spectroscopy was employed to experimentally probe water molecule dynamics.
• Density functional theory (DFT)-based molecular dynamics simulations were used to model the systems.
• Comparative studies were conducted on solutions of phenolate and phenol.

Main Results:

• Phenolate ions immobilize approximately 6.2 water molecules beyond the first solvation shell, with orientational relaxation times (τ_or) greater than 10 ps.
• Phenol immobilizes only about 2 water molecules, including those in the first solvation shell.
• Simulations accurately reproduced experimental findings, revealing that phenolate induces local ordering of hydrogen bonds extending beyond the first solvation shell.

Conclusions:

• The enhanced immobilization of water by phenolate is attributed to the high charge density of its oxygen atom, affecting water structure beyond the immediate vicinity.
• The negatively charged oxygen atom of phenolate plays a critical role in long-range solvation interactions.
• These findings highlight the significant impact of ionic charge on the organization of surrounding solvent molecules.