Selected biologically relevant ions at the air/water interface: a comparative molecular dynamics study

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Surface Science

Background:

• Understanding ion behavior at interfaces is crucial for various chemical and biological processes.
• The air/water interface presents unique challenges due to its distinct properties compared to bulk water.

Purpose of the Study:

• To investigate the interfacial behavior of biologically and technologically relevant ions at the air/water interface.
• To analyze the influence of ion hydrophobicity and counter-anions on interfacial adsorption.
• To compare ion segregation at the air/water interface with that at protein surfaces.

Main Methods:

• Molecular dynamics (MD) simulations were employed.
• Polarizable potentials were utilized to accurately model ion-water interactions.
• Density profiles were analyzed to quantify ion propensities for the air/water interface.

Main Results:

• Tetraalkylammonium (TAA) ion affinity for the air/water interface increases with hydrophobicity.
• Cations with propyl and butyl chains exhibit surfactant-like behavior.
• The effect of counter-anions (sulfate, chloride) on cation interfacial behavior was minimal.
• No correlation was found between ion segregation at the air/water interface and protein surfaces.

Conclusions:

• Ion hydrophobicity is a key determinant of interfacial behavior at the air/water interface.
• The air/water interface and protein surfaces exhibit distinct ion segregation patterns.
• Findings provide insights into ion solvation and interfacial phenomena.