Concentration of oxygen in lipid bilayers using a spin-label method

Area of Science:

• Biophysics
• Physical Chemistry
• Materials Science

Background:

• Lipid bilayers are fundamental components of cell membranes.
• Understanding the physical properties of lipid bilayers, such as oxygen solubility, is crucial for comprehending membrane function and dynamics.
• Previous methods for determining oxygen concentration in lipid phases were limited.

Purpose of the Study:

• To quantify the concentration of dissolved oxygen within the hydrocarbon region of lipid bilayers.
• To investigate the phase-dependent behavior of oxygen partitioning in dimyristoylphosphatidylcholine (DMPC) lipid bilayers.
• To determine the thermodynamic parameters governing the mixing of water and lipid in different phases.

Main Methods:

• Employed a novel electron spin resonance (ESR) technique utilizing a nitroxide-radical spin probe.
• Measured the partition coefficient of oxygen in DMPC lipid bilayers across different temperature phases.
• Calculated molar free energy, enthalpy, and entropy of mixing for water and lipid components.

Main Results:

• The partition coefficient of oxygen in DMPC was approximately 3 above the main transition temperature.
• A significant decrease in the partition coefficient to 0.2 was observed below the pretransition temperature.
• This indicates a substantial exclusion of oxygen from the crystalline phase of the lipid bilayer.

Conclusions:

• The electron spin resonance (ESR) method provides an effective means to determine oxygen concentration in lipid bilayers.
• Dimyristoylphosphatidylcholine (DMPC) lipid bilayers exhibit distinct oxygen partitioning behavior in fluid versus crystalline phases.
• Oxygen is largely excluded from the ordered crystalline phase, impacting membrane properties.