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High-Resolution NMR in Magnetic Fields with Unknown Spatiotemporal Variations

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Science  26 Jun 2009:
Vol. 324, Issue 5935, pp. 1693-1697
DOI: 10.1126/science.1175102

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NMR Under Stormy Conditions

Nuclear magnetic resonance spectroscopy is immensely useful for molecular characterization. However, the resolution necessary for making fine structural distinctions relies on sample isolation in a surrounding magnetic field that exhibits minimal variation in space and time over the course of the measurement; this requirement limits the range of materials that can be easily probed. Pelupessy et al. (p. 1693) present an approach that circumvents the need for spatiotemporal field homogeneity by detecting coherence transfer among coupled spins. Whereas prior methods have compensated for heterogeneity by applying corrective magnetic fields, this technique relies on the inherent insensitivity of the measured coherences to changes in the local magnetic environment and thus can be applied without prior knowledge of the field variation profile.

Abstract

Nuclear magnetic resonance (NMR) experiments are usually carried out in homogeneous magnetic fields. In many cases, however, high-resolution spectra are virtually impossible to obtain because of the inherent heterogeneity of the samples or living organisms under investigation, as well as the poor homogeneity of the magnets (particularly when bulky samples must be placed outside their bores). Unstable power supplies and vibrations arising from cooling can lead to field fluctuations in time as well as space. We show how high-resolution NMR spectra can be obtained in inhomogeneous fields with unknown spatiotemporal variations. Our method, based on coherence transfer between spins, can accommodate spatial inhomogeneities of at least 11 gauss per centimeter and temporal fluctuations slower than 2 hertz.

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