NMR studies of chloroform@cryptophane-A and chloroform@bis-cryptophane inclusion complexes oriented in thermotropic liquid crystals |
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Authors: | Chaffee Kathleen E Marjanska Malgorzata Goodson Boyd M |
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Institution: | Department of Chemistry and Biochemistry, 113 Neckers Hall, Southern Illinois University, Carbondale, IL 62901, USA. |
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Abstract: | Oriented inclusion complexes of chloroform@cryptophane-A and chloroform@bis-cryptophane were prepared using a nematic thermotropic liquid crystal (ZLI 1132), and the alignment and magnetic resonance properties of these host-guest systems were studied via (13)C NMR of the labeled guests. Large (1)H-(13)C dipolar splittings for (13)CHCl(3) guests indicated significantly enhanced (approximately 2-fold) ordering for the trapped vs. free ligands under all conditions studied, with similar ordering observed for the two complexes-despite significant differences in size and motional freedom between the hosts. For each environment, variable-temperature studies permitted the sign and magnitude of the order parameter for chloroform's C-H bond to be independently determined from the (13)C chemical shift anisotropy (CSA) shifts (via the gradient method) and the restored (1)H-(13)C dipolar couplings. In both systems, the results are consistent with overall alignment of the complexes such that the cage principal axis lies roughly perpendicular to the LC director. |
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