This chapter discusses Two-dimensional (2D) implementations of the separation procedures. The techniques described can be generalized to higher dimensions. 2D exchange spectroscopy is a very convenient tool for studying dynamic processes in liquids. It is designed specifically for the elucidation of incoherent magnetization transfer processes: chemical exchange and cross-relaxation. However, the 2D exchange experiment also detects coherent magnetization transfer caused by scalar coupling. In laboratory-frame, 2D exchange spectra of macromolecules, cross-relaxation and chemical exchange are indistinguishable because both give rise to positive cross-peaks. In rotating-frame exchange spectra of macromolecules, cross-relaxation and chemical exchange are distinguishable because cross-peaks of the former are negative with respect to the diagonal whereas those of the latter are positive. However, for 2D exchange spectroscopy, only slow processes in which the observed spins change their resonance frequencies are suitable. In NMR spectroscopy, slow refers to an exchange rate, kij, between sites i and j that is smaller than the difference in the resonance frequencies of the two exchange sites—that is, exchange does not influence the shapes and positions of the individual resonance lines.
ASJC Scopus subject areas
- Molecular Biology