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In magnetic resonance spectroscopy, the transfer of spin polarization from one spin population to another via cross-relaxation is generally called the Overhauser Effect, after American physicist Albert Overhauser who hypothesized it while a postgraduate student in the early 1950s. The phenomenon was demonstrated experimentally by C. P. Slichter and T. R. Carver in 1953. The original Overhauser effect1 was described in terms of polarization transfer between electron and nuclear spins, but is now mostly used for transfer between nuclear spins—the Nuclear Overhauser Effect (NOE or nOe). A very common application is NOESY (Nuclear Overhauser Effect Spectroscopy), an NMR technique for structure determination of macromolecular motifs.
NOE differs from spin coupling in the respect that NOE is observed through space, not through bonds. Thus, all atoms that are in close proximity to each other give a NOE, whereas spin coupling is observed only when the atoms are bonded to same or neighboring atoms. Furthermore, the distance can be derived from the observed NOEs, so that the precise, three-dimensional structure of the molecule can be reconstructed.
Other experimental techniques exploiting the NOE include and are not limited to:
- HOESY, Heteronuclear Overhauser Effect Spectroscopy
- ROESY, Rotational Frame Nuclear Overhauser Effect Spectroscopy
- TRNOE, Transferred Nuclear Overhauser Effect
- DPFGSE-NOE, Double Pulsed Field Gradient Spin Echo NOE experiment
References
- ^ A.W. Overhauser, Phys. Rev. 92, 411 (1953).
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