Coherence pathway selection by cogwheel phase cycling in liquid-state NMR

Coherence selection as an integral element of most multipulse NMR methods also represents a bottleneck to the efficiency of multidimensional NMR methods. in particular, phase cycling often requires total scan numbers in excess of signal-to-noise demands. M. H. Levitt and coworkers have recently introduced cogwheel phase cycling in solid-state NMR, which improves on this problem. In this article we recapitulate the principles of coherence selection in multipulse and multidimensional NMR. The fundamental differences between various coherence selection strategies are discussed, and examples of implementing cogwheel phase cycling in liquid-state NMR experiments commonly used for biopolymers are given. Design guidelines are suggested for incorporating cogwheel phase cycles into other pulsed NMR techniques. For experiments with multiple coherence transfer steps, cogwheel phase cycling is more efficient in spectrometer time usage than traditional nested phase cycling, as the scan numbers can be adjusted in smaller steps. Even compared with pulsed field gradient selection methods advantages exist, especially for fast relaxing resonances. (C) 2007 Wiley Periodicals, Inc.