Spatial/spectral encoding of the spin interactions in ultrafast multidimensional NMR.

Two-dimensional nuclear magnetic resonance (2D NMR) spectroscopy provides the means to extract diverse physical, chemical, and biological information at an atomic level. Conventional sampling schemes, however, may result in relatively long 2D experiments; this has stimulated the search for alternative, rapid acquisition schemes. Among the strategies that have been recently proposed for achieving this counts an "ultrafast" approach, relying on the spatial encoding of the indirect domain evolution to provide arbitrary spectra within a single scan. A common feature of all spatial encoding schemes hitherto described is their uniform encoding of a continuous bandwidth of indirect-domain frequencies, regardless of the chemical sites' spectral distribution within it. These very general conditions, however, are often associated with a number of tradeoffs and compromises in the spectral widths and resolutions that can be achieved for both the direct and indirect domains. This paper proposes a different strategy for single-scan acquisition of 2D spectra, which performs an optimal encoding by employing a priori information regarding the positions of NMR resonances along the indirect domain. We denote this as "spatial/spectral encoding"; the underlying principles of this new approach, together with experimental results based on uni- and multidimensional rf pulse schemes, are presented.