Molecular Orientation at the Squalene/Air Interface from Sum Frequency Generation Spectroscopy and Atomistic Modeling

Area of Science:

• Environmental Chemistry
• Atmospheric Chemistry
• Biochemistry

Background:

• Human skin oils are a major source of organic compounds indoors.
• Squalene is a key component of skin lipids and reacts with atmospheric oxidants.
• Understanding squalene's behavior at interfaces is crucial for indoor air quality.

Purpose of the Study:

• To investigate the conformational and orientational preferences of squalene at the air/oil interface.
• To determine how squalene's structure at the interface affects its reactivity with ozone.
• To assess the implications for indoor air chemistry models.

Main Methods:

• Combined spectroscopic analysis and atomistic molecular modeling.
• Simulations of squalene at the air/oil interface.
• Analysis of squalene's molecular orientation and double bond accessibility.

Main Results:

• Squalene molecules exhibit a preference for aligning with the surface normal.
• This alignment leads to differential accessibility and reactivity of squalene's double bonds.
• Water molecules were detected at the surface of the hydrophobic squalene layer.

Conclusions:

• Squalene's surface orientation significantly influences its reaction rate with ozone indoors.
• The presence of water at the interface may affect squalene's reactivity.
• Findings necessitate refinement of kinetic models for indoor air chemistry involving skin oils.