Estimation of Gel and Fluid Domain Sizes in Two-Component Lipid Bilayers
The widths and shapes of electron spin resonance (ESR) spectroscopic lines were analyzed to determine the average size of gel and fluid domains in a two-component, two-phase lipid bilayer system. The ratio of the maximum peak-to-peak amplitude to the amplitude in the wings of electron spin resonance spectral lines from a spin labelled lipid was found to be diagnostic of the connectedness of the system. Analysis of the ESR lineshapes suggested that for a statistical distribution of the spin labels in disconnected domains, the intensity ratio is always greater than the value for connected domains. The intensity ratio was calculated as a function of the average number of spin labels per domain. This method was applied to the binary mixtures of dimyristoyl phosphatidylcholine (DMPC) with distearoyl phosphatidylcholine (DSPC) probed with a spin labelled derivative of DMPC. The results suggest that the size of the fluid (or gel) domains increases with increasing fluid (or gel) mole fraction.
KeywordsElectron Spin Resonance Electron Spin Resonance Spectrum Spin Label Coexistence Region Lineshape Analysis
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