Lateral diffusion of bilayer lipids measured via 31P CODEX NMR

We have employed 31P CODEX (centre-band-only-detection-of-exchange) NMR to measure lateral diffusion coefficients of phospholipids in unilamellar lipid bilayer vesicles consisting of 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC), alone or in mixtures with 30 mol% 1-palmitoyl-2-oleoyl-phosphatidylglycerol (POPG) or cholesterol (CHOL). The lateral diffusion coefficients of POPC and POPG were extracted from experimental CODEX signal decays as a function of increasing mixing time, after accounting for the vesicle's size and size distribution, as determined via dynamic light scattering, and the viscosity of the vesicular suspension, as determined via 1H pulsed field gradient NMR. Lateral diffusion coefficients for POPC and POPG determined in this fashion fell in the range 1.0–3.2 × 10−12 m2 s−1 at 10 °C, depending on the vesicular composition, in good agreement with accepted values. Thus, two advantages of 31P CODEX NMR for phospholipid lateral diffusion measurements are demonstrated: no labelling of the molecule of interest is necessary, and multiple lateral diffusion coefficients can be measured simultaneously. It is expected that this approach will prove particularly useful in diagnosing heterogeneities in lateral diffusion behaviours, such as might be expected for specific lipid–lipid or lipid–protein interactions, and thermotropic or electrostatically induced phase inhomogeneities.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlight► 31P CODEX was used to determine lipid lateral diffusion coefficients in LUVs. ► Multiple diffusion coefficients could be measured simultaneously without labelling. ► CODEX decays of LUVs were measured along with the viscosity and radii distribution. ► This data was used to determine diffusion coefficients via least squares analysis. ► Diffusion coefficients obtained were similar to literature values.