Recent progress in understanding hydrophobic interactions.

Area of Science:

• Physical Chemistry
• Surface Science
• Biophysics

Background:

• The hydrophobic effect describes low solute solubility in water.
• Hydrophobic interaction is the strong attraction between hydrophobic surfaces in water.
• This interaction is crucial for processes like protein folding and micelle formation.

Purpose of the Study:

• To review direct force measurements of hydrophobic interactions.
• To differentiate between long-range and short-range hydrophobic attractions.
• To identify the true nature of hydrophobic interactions at the molecular level.

Main Methods:

• Direct force measurements between macroscopic hydrophobic surfaces in aqueous solutions.
• Utilizing Surface Force Apparatus (SFA) and Atomic Force Microscopy (AFM).
• Analysis of interaction ranges from angstroms to thousands of angstroms.

Main Results:

• Reported attraction ranges between hydrophobic surfaces have expanded significantly over decades.
• Long-range attraction (>200 Angstrom) is explained by recent advancements.
• Short-range attraction (<100 Angstrom) is tentatively identified as the true hydrophobic interaction.

Conclusions:

• The true hydrophobic interaction likely occurs at short ranges (<100 Angstrom).
• Further research is needed for a quantitative explanation of short-range hydrophobic forces.
• A stronger, uncharacterized force may dominate at molecular contact (<10 Angstrom).