Chapter 4: Cyclodextrin Inclusion Compounds
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Published:10 Nov 2011
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Special Collection: 2011 ebook collection , 2011 ebook collection , 2011-2015 analytical chemistry subject collection
Circular Dichroism and Magnetic Circular Dichroism Spectroscopy for Organic Chemists, The Royal Society of Chemistry, 2011, ch. 4, pp. 93-103.
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The use of cyclodextrin (CyD) inclusion compounds to study the circular dichroism (CD) spectra of guest molecules trapped in the central cavity is described in detail. Host-guest complexes with clearly defined geometries are readily formed in solution, which enables an analysis of the alignment of band polarisations at wavelengths as short as 200 nm even in the absence of single crystals. The orientation of the chromophore within the CyD cavity can be elucidated by analysing the CD spectra, or alternatively, if the inclusion type has been established, the direction of the electric dipole transition moment (edtm) can be determined instead. Since CyDs are composed of chiral glucose units, the CD signal is induced in the absorption bands of the achiral guest molecules and the rotational strength values of intense electric dipole allowed bands can be determined using the coupled oscillator model of Kirkwood. CyD complexes of pyrene, diaminonaphthalenes and the pyrene-1,3,6,8-tetrasulfonate anion provide examples of the use of CD spectroscopy to identify axial, equatorial and lid type inclusions, respectively, while CyD complexes of biphenyls, bipyridyls and ferrocenes provide examples of the use of known axial inclusion structures to determine the alignment of the edtms of the major electronic transitions of the guest molecule.