Abstract
The position Ho of the ESR central absorption maximum of a spin-labeled phospholipid dispersion was recorded in the manner of a g-factor; γ=hν/βHo. The point Ho corresponds to the center line zero crossing point of the first derivative ESR spectrum. A 5-doxyl derivative of stearic acid was incorporated into dispersions of dipalmitoyl phosphatidyl choline and dipalmitoyl phosphatidyl ethanolamine formed either by shaking a lipid film in the presence of buffered saline or by dialysis of label and lipid in 2-chloroethanol against buffered saline. It was found that during the gel to liquid crystal phase transition, the decrease in the order parameter, S, ranged from about .045 to .06 and the increase in the parameter γ ranged from about .0001 to .0002 depending upon the lipid and preparation method. In all cases examined, the changes could be associated with the lipid phase transition. A simple model based on rapid anisotropic motion indicates that about a 38% decrease in line width accounts for the observed shift in γ.
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