The diffusion-solubility of oxygen in lipid bilayers

Area of Science:

• Biophysics
• Physical Chemistry
• Materials Science

Background:

• Understanding oxygen transport in biological membranes is crucial for cellular respiration and drug delivery.
• Phosphatidylcholine bilayers serve as a model system for cell membranes.
• Previous studies have measured oxygen diffusion and solubility separately, but their combined product (Doα) provides a more comprehensive view of oxygen transport dynamics.

Purpose of the Study:

• To determine the product of oxygen diffusion coefficient (Do) and oxygen solubility (α), denoted as Doα, in phosphatidylcholine bilayers.
• To investigate the spatial variation of Doα across the bilayer using electron spin resonance (ESR) spin-exchange measurements.
• To compare the results with those obtained from fluorescence-quenching experiments.

Main Methods:

• Electron spin resonance (ESR) spin-exchange measurements were employed to determine Doα.
• Fatty acid spin labels were utilized to probe Doα at different positions perpendicular to the bilayer surface.
• Measurements were conducted at temperatures above the lipid phase transitions.

Main Results:

• The determined values of Doα from ESR spin-exchange experiments were in good agreement with fluorescence-quenching data.
• Doα was found to be strongly dependent on the position perpendicular to the bilayer surface.
• The highest values of Doα were observed in the center of the bilayer, while the lowest values were found near the bilayer head groups.

Conclusions:

• The product of oxygen diffusion and solubility (Doα) exhibits significant spatial heterogeneity within phosphatidylcholine bilayers.
• Oxygen transport is most efficient in the hydrophobic core of the bilayer and less efficient near the polar head groups.
• ESR spin-exchange is a valuable technique for spatially resolved measurements of oxygen transport properties in lipid membranes.