Measuring Molecular Forces With Atomic Force Microscopy 1: Solvent Influence on Hydrophobic Interactions

Area of Science:

• Physical Chemistry
• Surface Science
• Biophysics

Background:

• Hydrophobic interactions are fundamental to molecular self-assembly, protein folding, and aggregation.
• The precise origins and characteristics of hydrophobic forces, including their strength and range compared to van der Waals (vdW) forces, are not fully understood.
• Potential contributing factors include water structuring, polarization effects, and entropic contributions.

Purpose of the Study:

• To investigate the impact of solvent polarity on hydrophobic interactions.
• To explore the behavior of hydrophobic forces in water:DMSO binary solvent mixtures.
• To contribute to understanding the fundamental mechanisms driving hydrophobic phenomena.

Main Methods:

• Preparation of fluorocarbon surfaces on gold substrates using chemical vapor deposition (CVD).
• Utilized atomic force microscopy (AFM) to measure force-distance curves.
• Applied an extended van der Waals (vdW) model to analyze the measured forces.

Main Results:

• Characterized hydrophobic interactions between surfaces in varying water:DMSO mixtures.
• Quantified the influence of medium polarity on the measured hydrophobic forces.
• Demonstrated that solvent composition significantly alters hydrophobic interaction profiles.

Conclusions:

• Hydrophobic interactions are strongly modulated by the polarity of the surrounding solvent medium.
• The study provides experimental insights into the nature of hydrophobic forces.
• Findings contribute to a deeper understanding of molecular interactions in complex solvent systems.