Singlet states open the way to longer time-scales in the measurement of diffusion by NMR spectroscopy

Abstract

Nuclear magnetic resonance is a powerful nonintrusive technique for measuring diffusion coefficients through the use of pulsed field gradients. The main limitation to the application range of this method is imposed by the relaxation time constants of the magnetization. The recently introduced singlet-state spectroscopy affords obtaining relaxation time constants for pairs of coupled spins which can be longer by more than an order of magnitude than the spin-lattice relaxation time constants. We review in this paper the advantages that are offered by these long relaxation time constants for diffusion measurements. Using experiments that combine singlet-state and diffusion spectroscopy, slower diffusion constants can be determined. The coupling of the two methods constitutes an alternative to the use of special probes equipped with strong gradients for the study of large molecules that diffuse slowly in solution. © 2008 Wiley Periodicals, Inc.