Solute partitioning into lipid bilayer membranes.

Area of Science:

• Biophysics
• Physical Chemistry
• Membrane Science

Background:

• Lipid bilayers are fundamental to cell membranes.
• Understanding solute partitioning is crucial for drug delivery and membrane function.
• Previous models often treated membranes as simple oil phases.

Purpose of the Study:

• To quantify the effect of phospholipid chain surface density on benzene partitioning into lipid bilayers.
• To investigate the physical factors governing solute exclusion in membranes.
• To compare membrane partitioning with partitioning into bulk phases.

Main Methods:

• Utilized 2H Nuclear Magnetic Resonance (NMR) for precise measurement of phospholipid chain surface densities.
• Compared NMR results with X-ray diffraction data for validation.
• Measured membrane/water partition coefficients of benzene.

Main Results:

• Benzene partitioning into lipid bilayers is strongly dependent on phospholipid chain surface density.
• Increasing surface density from 50% to 90% reduced benzene partitioning by an order of magnitude.
• This solute exclusion effect was independent of temperature, cholesterol, and phospholipid chain length.

Conclusions:

• Solute partitioning into lipid bilayers is fundamentally different from partitioning into bulk oil phases.
• Entropic effects related to phospholipid chain ordering drive solute exclusion.
• Findings support statistical thermodynamic theories of interfacial solute partitioning.