Temperature Dependence of Hydrotropy.

Area of Science:

• Physical Chemistry
• Thermodynamics
• Solution Chemistry

Background:

• Hydrophobic solutes exhibit increased solubility in water with rising temperatures when hydrotropes are present.
• The underlying mechanism of hydrotropic solubilization, particularly its temperature dependence, requires detailed explanation.

Purpose of the Study:

• To elucidate the thermodynamic mechanism behind temperature-dependent hydrotropic solubilization.
• To differentiate the roles of local hydrotrope-solute interactions and bulk hydrotrope self-association.

Main Methods:

• Statistical thermodynamics was employed to analyze the system.
• The study focused on the interplay between temperature and hydrotrope concentration.
• Analysis considered local (solute-surrounding) and bulk (solution) properties.

Main Results:

• Two key factors influence temperature dependence: enhanced local enthalpy-hydrotrope correlation and suppressed temperature dependence due to bulk hydrotrope self-association.
• For urea as a hydrotrope, the local effect dominates, indicating weakened interaction energies around the solute.
• Local hydrotrope accumulation around the solute is driven by enhanced self-association and accompanied by weakened energetic interactions.

Conclusions:

• Hydrotropic solubilization is a complex phenomenon influenced by both local and bulk solution properties.
• The temperature dependence of solubility is modulated by the balance between local hydrotrope-solute interactions and hydrotrope self-association.
• Water molecules play a crucial mediating role in the fluctuational nature of hydrotrope association.