Nuclear Magnetic Resonance

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Nature Physics 2, 105 - 109 (2006)
Published online: 22 January 2006 | doi:10.1038/nphys211
Subject Categories: Chemical physics | Atomic and molecular physics

Chemical analysis by ultrahigh-resolution nuclear magnetic resonance in the Earth’s magnetic field

Stephan Appelt1, Holger Kühn1, F. Wolfgang Häsing1 & Bernhard Blümich2


High-resolution NMR spectroscopy is a powerful tool for non-destructive structural investigations of matter1. Typically, expensive and immobile superconducting magnets are required for chemical analysis by high-resolution NMR spectroscopy. Here we present the feasibility of liquid-state proton (1H), lithium (7Li) and fluorine (19F) ultrahigh-resolution NMR spectroscopy2 in the Earth’s magnetic field. We show that in the Earth’s field the transverse relaxation time T2 of the 7Li nucleus is very sensitive to its mobility in solution. The J-coupling constants3 of silicon-containing (29Si) and fluorine-containing molecules are measured with just a single scan. The accuracy of the measured 1H–29Si and 1H–19F J-coupling constants is between a few millihertz up to 20 mHz. This is at least one order of magnitude better than the precision obtained with superconducting magnets. The high precision allows the discrimination of similar chemical structures of small molecules as well as of macromolecules.

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Earth's Field Nuclear Magnetic Resonance (NMR)

URL: URL: Retrieved by DonEMitchell 13:08, 23 December 2011 (MST)

Near-zero-Field nuclear magnetic resonance[1]

M. P. Ledbetter,1,*, T. Theis,2, 3 J. W. Blanchard,2, 3 H. Ring,2, 3 P. Ganssle,2, 3 S. Appelt,4 B. Blumich,5 A. Pines,2, 3 and D. Budker1, 6

1Department of Physics, University of California at Berkeley, Berkeley, California 94720-7300
2Department of Chemistry, University of California at Berkeley, Berkeley, California 94720-3220
3Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley CA 94720
4Central Institute for Electronics, Research Center Julich, D-52425 Julich, Germany
5Institute of Technical and Macromolecular Chemistry,RWTH Aachen University, 52056 Aachen, Germany
6Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley CA 94720
*Electronic address

(Dated: July 11, 2011)

We investigate nuclear magnetic resonance (NMR) in near-zero-field, where the Zeeman interaction can be treated as a perturbation to the electron mediated scalar interaction (J-coupling). This is in stark contrast to the high field case, where heteronuclear J-couplings are normally treated as a small perturbation. We show that the presence of very small magnetic fields results in splitting of the zero-field NMR lines, imparting considerable additional information to the pure zero-field spectra. Experimental results are in good agreement with first-order perturbation theory and with full numerical simulation when perturbation theory breaks down. We present simple rules for understanding the splitting patterns in near-zero-field NMR, which can be applied to molecules with non-trivial spectra.
PACS numbers: 82.56.Fk, 33.25.+k, 71.70.Ej, 33.57.+c

[1]: The near-zero field is the high-strength magnetic field used in NMR. -dem

URL: Retrieved DonEMitchell 12:48, 23 December 2011 (MST)


Analytical Methods

NMR Source:

Nuclear magnetic resonance (NMR) is based upon the measurement of absorption of radiofrequency (RF) radiation by a nucleus in a strong magnetic field. Absorption of the radiation causes the nuclear spin to realign or flip in the higher-energy direction. After absorbing energy the nuclei will re-emit RF radiation and return to the lower-energy state.

The principle of NMR is that nuclei with odd number of protons, neutrons or both will have an intrinsic nuclear spin. When a nucleus with a non-zero spin is placed in a magnetic field, the nuclear spin can align in either the same direction or in the opposite direction as the field. These two nuclear spin alignments have different energies and application of a magnetic field lifts the degeneracy of the nuclear spins. A nucleus that has its spin aligned with the field will have a lower energy than when it has its spin aligned in the opposite direction to the field.

The energy of a NMR transition depends on the magnetic-field strength and a proportionality factor for each nucleus called the magnetogyric ratio. The local environment around a given nucleus in a molecule will slightly perturb the local magnetic field exerted on that nucleus and affect its exact transition energy. This dependence of the transition energy on the position of a particular atom in a molecule makes NMR spectroscopy extremely useful for determining the structure of molecules.

NMR spectroscopy is one of the most powerful tools for elucidating the structure of both organic and inorganic species. It has also proven useful for the quantitative determination of absorbing species.

See also

Earth's Field NMR Instrument