New NMR Experiments in Liquids

Instrumental Requirements. The topic New Experiments is specifically intended to cover new ways of generating spectroscopic information. That is, the techniques are not specifically oriented toward one 

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The principal dilTerence from liquid-state NMR is that the interactions which are averaged by molecular motion on the NMR timescale in liquids lead, because of their anisotropic nature, to much wider lines in solids. Extra infonnation is, in principle, available but is often masked by the lower resolution. Thus, many of the teclmiques developed for liquid-state NMR are not currently feasible in the solid state. Furthemiore, the increased linewidth and the methods used to achieve high resolution put more demands on the spectrometer. Nevertheless, the field of solid-state NMR is advancing rapidly, with a steady stream of new experiments forthcoming. 

Figure 6-17 Diagram of COSY and relayed coherence transfer (RCT) experiments for two three-spin systems (AMX and A M X ) whose M and M portions overlap. (Adapted from F. J. M. van de Yen, Multidimensional NMR in Liquids, VCH, New York,...

In liquid-state NMR, spin relaxation due to cross-correlation of two anisotropic spin interactions can provide useful information about molecular structure and dynamics. These effects are manifest as differential line widths or line intensities in the NMR spectra. Recently, new experiments were developed for the accurate measurement of numerous cross-correlated relaxation rates in scalar coupled multi-spin systems. The recently introduced concept of transverse relaxation optimized spectroscopy (TROSY) is also based on cross-correlated relaxation. Brutscher outlined the basic concepts and experimental techniques necessary for understanding and exploiting cross-correlated relaxation effects in macromolecules. In addition, he presented some examples showing the potential of cross-correlated relaxation for high-resolution NMR studies of proteins and nucleic acids. 

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