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 diffusion coefficients for motion perpendicular to the director axis for 4-oxo2,2,6,6,-tetramethylpiperidine-l-oxyl (TEMPONE) and octylbenzoyl spin label (OBSL) in the nematic phase of Phase V have been determined. They are D(TEMPONE) = 1.25 × 10^-7 cm² s^-1 and D(OBSL) = 0.48 × 10^-7 cm² s^-1 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 × 10^-8 to 2 × 10^-7 cm² s^-1. Activation energies for diffusion in the two systems are E_a(CSL/POPC) = 6.30 kcal mol^-1 and E_a(16PC/DMPC) = 8.63 kcal mol^-1.