Concepts in NMR, updated to March 2007

Coherence pathway selection by cogwheel phase cycling in liquid-state NMR
Gerhard Zuckerstätter, Norbert Müller *
Institute of Organic Chemistry, Johannes Kepler University, Altenbergerstrasse 69, A-4040 Linz, Austria

*Correspondence to Norbert Müller, Institute of Organic Chemistry, Johannes Kepler University, Altenbergerstrasse 69, A-4040 Linz, Austria

Keywords
cogwheel phase cycling • coherence order • coherence transfer pathways • coherence selection • phase cycling • triple resonance

Abstract
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. © 2007 Wiley Periodicals, Inc. Concepts Magn Reson Part A 30A: 81-99, 2007.
Received: 21 September 2006; Revised: 21 December 2006; Accepted: 21 December 2006

Digital Object Identifier (DOI)
10.1002/cmr.a.20079

A practical guide for solid-state NMR distance measurements in proteins
Frank A. Kovacs, Daniel J. Fowler, Gregory J. Gallagher, Lynmarie K. Thompson *
Department of Chemistry, University of Massachusetts Amherst, Amherst, Massachusetts

*Correspondence to Lynmarie K. Thompson, Department of Chemistry, University of Massachusetts Amherst, Amherst, Massachusetts

Keywords
rotational resonance • R2 • REDOR • MAS • solid-state NMR • site-directed distance measurements

Abstract
Rotational resonance (R2) and rotational echo double resonance (REDOR) are powerful solid-state NMR techniques that can be applied in a site-directed fashion for precise distance measurements in proteins. These tools are well suited for systems in which a few precise distance measurements are needed to understand a mechanism or map a binding site, particularly if this information is unavailable from x-ray crystallography or solution NMR, as is often the case for membrane proteins. Strategies and challenges in the design and implementation of such experiments are described and illustrated with experiments probing mechanisms of transmembrane signaling in bacterial chemotaxis receptors. © 2007 Wiley Periodicals, Inc. Concepts Magn Reson Part A 30A: 21-39, 2007.
Received: 27 July 2006; Accepted: 28 August 2006

Digital Object Identifier (DOI)

10.1002/cmr.a.20071