Observation of Translational Diffusion in a Planer Supported Lipid Bilayer Membrane by Total Internal Reflection-Transient Grating Method

Total internal reflection-transient grating (TIR-TG) method has been applied to diffusion coefficient measurements of trans-stilbene in a dimyristoylphosphatidylcholine (DMPC) lipid bilayer membrane at a silica/water interface. The observed TIR-TG signal consisted of four decay components. The rate constants of the third and fourth components quadratically depended on grating wavenumbers, which indicates that these components represent diffusion processes of trans-stilbene (diffusion signals). From the decay rate constants of the diffusion signals, two different diffusion coefficients, (5.7 ± 1.0) × 10−10 and (2.8 ± 0.5) × 10−12 m2s−1 were obtained for trans-stilbene in the DMPC membrane. This result indicates that the DMPC membrane is an inhomogeneous environment that can be described with two different effective viscosities.