NMR studies of cyclodextrin inclusion complexes with nitrophenols.
Item
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Title
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NMR studies of cyclodextrin inclusion complexes with nitrophenols.
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Identifier
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AAI9830782
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identifier
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9830782
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Creator
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Yuan, Lixun.
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Contributor
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Adviser: Theodore Axenrod
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Date
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1998
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Language
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English
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Publisher
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City University of New York.
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Subject
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Chemistry, Analytical | Chemistry, Organic
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Abstract
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The inclusion complexes of {dollar}\alpha{dollar}-cyclodextrin ({dollar}\alpha{dollar}-CD) and permethylated {dollar}\alpha{dollar}-cyclodextrin ({dollar}\alpha{dollar}-MCD) with the two nitrophenols, 4-nitrophenol (4-NP) and 2,6-dimethyl-4-nitrophenol (2,6-DM-4-NP), were studied by means of {dollar}\sp{15}{dollar}N-{dollar}\sp1{dollar}H heteronuclear Overhauser enhancement (NOE) experiments. Based on the enhancements of {dollar}\sp{15}{dollar}N resonances of the 4-nitrophenols upon irradiation at resonances of H-3 and H-5 inner protons in the cyclodextrin cavity, the results support the structures of these inclusion complexes. In these structures, the nitrophenols are preferentially inserted with the nitro group head first into the CD cavities and penetrated less deeply in the cavity of permethylated {dollar}\alpha{dollar}-CD than that of its parent cyclodextrin. Furthermore, these results are consistent with those derived from complexation-induced {dollar}\rm\sp1H,\ \sp{13}C{dollar} and {dollar}\sp{15}{dollar}N chemical shifts and NOESY experiments. The {dollar}\sp{15}{dollar}N spin-lattice relaxation time (T{dollar}\sb1{dollar}) was determined for the complexes of nitrophenols with {dollar}\alpha{dollar}- and {dollar}\beta{dollar}-cyclodextrins, and permethylated {dollar}\alpha{dollar}-cyclodextrin. The values obtained indicate that the complexes of {dollar}\alpha{dollar}-cyclodextrin with nitrophenols show weaker binding than the corresponding permethylated {dollar}\alpha{dollar}-cyclodextrin complexes and stronger binding than the corresponding {dollar}\beta{dollar}-cyclodextrin complexes. This observation supports the conclusion derived from the {dollar}\sp{15}{dollar}N-{dollar}\sp1{dollar}H NOE experiments. The method of using {dollar}\sp{15}{dollar}N-{dollar}\sp1{dollar}H nuclear Overhauser enhancement, while limited to guest molecules containing nitrogen, is shown to be useful when the dipolar interactions between protons involved in the cyclodextrin complex are too small to be measured. The advantage of using the {dollar}\sp{15}{dollar}N-{dollar}\sp1{dollar}H NOE experiment is due to the large magnitude of the {dollar}\sp{15}{dollar}N resonance enhancement (maximum 400%), compared to that of the {dollar}\sp1{dollar}H-{dollar}\sp1{dollar}H homonuclear NOE enhancement (maximum 50%).
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
