EFFECTS OF CHEMICAL-EXCHANGE IN DIFFUSION-ORDERED 2D NMR-SPECTRA

Diffusion-ordered 2D NMR spectra (DOSY) are generated by the transformation of PFG NMR data sets associated with each point on the chemical-shift axis. Here the effects of chemical exchange in DOSY are investigated, and the two-site problem is treated in detail. Expressions are derived for echo amplitudes as functions of K2, where K = γgδ is the gradient-pulse area, and these expressions are converted into diffusion spectra by means of an inverse Laplace transformation. The resulting spectra consist of δ functions at low exchange rates and Gaussian distributions at high exchange rates. The measurement of exchange rates by means of experimental diffusion spectra is possible under certain circumstances, but requires high signal-to-noise ratios and sophisticated data-inversion techniques. © 1993 Academic Press. All rights reserved.