Measurements of self-diffusion coefficients of monensin in chloroform solution by PFG-NMR

Abstract

The self-diffusion coefficients D of MonH·H ₂ O and MonNa have been measured by pulsed field gradient NMR (PFG-NMR) as a function of the concentration C. An exponential dependence of D on C has been found and explained on the basis of the free volume theory. The diffusion coefficients in the infinite dilute solution D(0) for MonH·H ₂ O and MonNa have been estimated by extrapolating to C=0 using the relationship between diffusion coefficient and solute concentration based on free volume theory. Valves of D(0) estimated in this way have been applied to the Stokes–Einstein equation in order to obtain Stokes' radii. The radius of MonNa (0.511 nm) was larger than that of MonH·H ₂ O (0.484 nm). These values were not very different from the radii of gyration (0.435 nm) in crystalline MonH·H ₂ O.