PARAMAGNETICALLY ENHANCED RELAXATION OF NUCLEAR SPINS - MEASUREMENT OF DIFFUSION

Paramagnetically enhanced relaxation nuclear magnetic resonance (PER-NMR) is a technique for measuring diffusion constants of paramagnetic solutes in liquids. The paramagnetic solute gives rise to enhanced relaxation of the nuclear spins of the solvent, and the enhancement is linear in solute concentration C. Measurement of dT1-1/dC and dT2-1/dC for solvent nuclei usually enables us to obtain the diffusion constant D and the distance of closest approach 2rc between the paramagnetic moment and the nuclear moment being studied. D is the average of the particle diffusion constant for the solute and of that for the solvent. The method is particularly useful in bilayers or membranes where conventional procedures fail and D varies with position across the bilayer. By measuring T1-1 and T2-1 for nuclei at different positions, [D/rC2] and [C/rC3] can be determined as a function of position. Some experimental results are presented along with a discussion of the uses and shortcomings of the PER-NMR technique. Our result suggests that the Stokes-Einstein relation between D and viscosity (η) holds quite well over nearly five orders of magnitude of η. © 1979 American Chemical Society.