Rapid Determination of Translational Diffusion Coefficients Using ESR Imaging*

The use of ESR imaging for the rapid determination of diffusion coefficients, D, in anisotropic solvents is reported, and the use of Fourier transforms of the concentration profile to determine D is discussed. An approximate rapid analysis technique is also presented. The ditfusion coefficients for motion perpendicular to the director axis for 4-0x02,2,6,6,-tetramethylpiperidine-I-oxyl (TEMPONE) and octylbenzoyl spin label (OBSL) in the nematic phase of Phase V have been determined. They are D(TEMPONE) = 1.25 X lo-’ cm* SK’ and D(OBSL) = 0.48 X lo-’ cm* s-’ at 294 K. The lateral diffusion coefficients for cholestane spin label (CSL) in POPC and 16PC in DMPC were also determined. The diffusion coefficients were measured as a function of temperature from 11 to 60°C and they range from 4 X 10-a to 2 X lo-’ cm* SK‘. Activation energies for diffusion in the two systems are E.(CSL/POPC) = 6.30 kcal mol-’ and E.( 16PC/DMPC) = 8.63 kcal mol-‘.