Cross-Polarisation Applied to the Study of Liquid Crsytalline Ordering |
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Authors: | Krishna V Ramanathan and Neeraj Sinha |
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Institution: | (1) Universität Leipzig, Biotechnologisch-Biomedizinisches Zentrum, Nachwuchsgruppe Strukturaufklärung membranassoziierter Proteine mittels Festkörper-NMR ;(2) Universität Leipzig, Institut für Medizinische Physik und Biophysik;(3) Universität Leipzig, Institut für Medizinische Physik und Biophysik;(4) Universität Magdeburg, Klinik für Neurologie II;(5) Universität Leipzig, Institut für Medizinische Physik und Biophysik |
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Abstract: | Cross polarisation is extensively used in solid state NMR for enhancing signals of nuclei with low gyromagnetic ratio. However,
the use of the method for providing quantitative structural and dynamics information is limited. This arises due to the fact
that the mechanism which is responsible for cross polarisation namely, the dipolar interaction, has a long range and is also
anisotropic. In nematic liquid crystals these limitations are easily overcome since molecules orient in a magnetic field.
The uniaxial ordering of the molecules essentially removes problems associated with the angular dependence of the interactions
encountered in powdered solids. The molecular motion averages out intermolecular dipolar interaction, while retaining partially
averaged intramolecular interaction. In this article the use of cross polarisation for obtaining heteronuclear dipolar couplings
and hence the order parameters of liquid crystals is presented. Several modifications to the basic experiment were considered
and their utility illustrated. A method for obtaining proton–proton dipolar couplings, by utilizing cross polarisation from
the dipolar reservoir, is also presented. |
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