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  Deuteron NMR of methyl groups in the tunneling regime. A single crystal study of aspirin-CD3

Detken, A., Focke, P., Zimmermann, H., Haeberlen, U., Olejniczak, Z., & Lalowicz, Z. T. (1995). Deuteron NMR of methyl groups in the tunneling regime. A single crystal study of aspirin-CD3. Zeitschrift für Naturforschung, A: Physical Sciences, 50(1), 95-116. doi:10.1515/zna-1995-0113.

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 Creators:
Detken, Andreas1, Author              
Focke, Peter2, Author              
Zimmermann, Herbert3, 4, Author              
Haeberlen, Ulrich2, Author              
Olejniczak, Zbigniew, Author
Lalowicz, Z. T., Author
Affiliations:
1Emeritus Group Bioorganic Chemistry, Max Planck Institute for Medical Research, Max Planck Society, ou_1497711              
2Research Group Prof. Dr. Haeberlen, Max Planck Institute for Medical Research, Max Planck Society, ou_1497739              
3Department of Molecular Physics, Max Planck Institute for Medical Research, Max Planck Society, ou_1497705              
4Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Max Planck Society, ou_1497700              

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 Abstract: We report the first single crystal deuteron NMR spectra of CD3 groups which display the socalled ±ß, ±(|α| ± ß) and ±(2|α| ± ß) lines characteristic of rotational tunneling in a sufficiently clear manner to allow a quantitative comparison with the respective theory developed in 1988 by the group of W. Müller-Warmuth. The molecular system we study is aspirin-CD3. We recorded spectra for differently oriented single crystals and measured spin-lattice relaxation times T1 in a wide temperature range. At 12.5 K we exploit the dependence of the ±(|α| ± ß) and ±(2|α| ± ß) lines on the orientation of the applied field B0 for determining the equilibrium orientation of the CD3 group in the crystal lattice. The spectra display features which allow, by comparison with simulated spectra, a measurement of the tunnel frequency vt. Its low temperature limit is (2.7 ± 0.1) MHz. It allows to infer the height V3 of the potential V(φ) in which the CD3 group moves, provided that this potential is purely threefold. We get V3 = (47.2 ± 0.5) meV. The transition from the tunneling to the classical, fast reorienting regime occurs in the 15 K ≲ T ≲ 35 K temperature range. In this range we observe a broadening, merging and eventually narrowing of the ± |α| and ±2|α| lines in very much the way predicted by Heuer. His theory, however, must be extended by taking into account all librational levels. The behaviour of the ± ß lines in the transition temperature range signalizes a reduction of the observable tunnel frequency with increasing temperature. This reduction allows an independent measurement of the potential height and represents a test of the assumption of a purely threefold potential. From the T1 -data we derive the temperature dependence of the correlation time Ƭc of the reorientational jumps. The plot of log Ƭc vs. 1 /T follows a straight line for more than five decades. From its slope we get yet another independent number for the potential height. It agrees well with the other ones, which confirms the assumption of the essentially threefold potential V(φ) in aspirin-CD3.

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Language(s): eng - English
 Dates: 1994-10-042014-06-021995-01-01
 Publication Status: Published in print
 Pages: 22
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 Rev. Type: Peer
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Title: Zeitschrift für Naturforschung, A: Physical Sciences
  Other : Z. Naturforsch., A: Phys. Sci.
Source Genre: Journal
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Publ. Info: Tübingen : Verlag der Zeitschrift für Naturforschung
Pages: - Volume / Issue: 50 (1) Sequence Number: - Start / End Page: 95 - 116 Identifier: ISSN: 1865-7109
CoNE: https://pure.mpg.de/cone/journals/resource/954928567579