Multidimensional Nuclear Magnetic Resonance of Biomolecules
Nuclear Magnetic Resonance and Electron Spin Resonance Spectroscopy
Published Online: 13 JUN 2008
Copyright © 2000 John Wiley & Sons, Ltd. All rights reserved.
Encyclopedia of Analytical Chemistry
How to Cite
Craik, D. J., Horne, J. and Scanlon, M. J. 2008. Multidimensional Nuclear Magnetic Resonance of Biomolecules. Encyclopedia of Analytical Chemistry. .
- Published Online: 13 JUN 2008
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Nuclear magnetic resonance (NMR) is associated with transitions, induced by radiofrequency (RF) irradiation, between energy levels of nuclei with nonzero spin quantum numbers in a magnetic field. Traditional “one-dimensional” (1-D) NMR spectra are presented as a plot of signal intensity versus applied frequency and provide information about the chemical environment of magnetically active nuclei. This is used to deduce information about the chemical structure and dynamics of molecules containing the magnetically active nuclei (most often protons). The frequencies of individual nuclei are referred to as their chemical shifts. Multidimensional NMR encompasses a range of related techniques, based on the application of a variety of precisely timed RF pulses to the sample, which extends traditional 1-D NMR into two-, three-, or four-frequency dimensions. These additional frequency dimensions may be the same as the first frequency dimension, referred to as homonuclear multidimensional NMR, or different, referred to as heteronuclear NMR. In multidimensional NMR of biomolecules, the most common frequencies correspond to 1H in the directly detected dimension and one or more of 1H, 13C, or 15N in the additional dimensions. Peaks in such spectra are defined by their intensity and frequency coordinates in two, three, or four dimensions obtained by extrapolation back to the respective frequency axes, which are in turn determined by the nature of the applied RF pulse sequences. The intensity and chemical shifts of such peaks provide information about the chemical environment, molecular connectivity, or spatial proximity of the participating nuclei. Multidimensional NMR has major advantages over 1-D NMR: reduction of peak overlap and provision of information on connectivity (either through bonds or through space). Multidimensional NMR spectroscopy of biomolecules is usually done for samples in solution at millimolar concentration. Where experiments require the use of 13C or 15N frequencies, it is usually necessary to isotopically enrich the macromolecule with these nuclei to >90%. This is readily achieved with modern molecular biology techniques and does not present a major limitation. The biggest limitation relates to molecular size, with studies generally limited to macromolecules of less than approximately 35 kDa.