Inclusion of Hydroxycinnamic Acids in Methylated Cyclodextrins: Host-Guest Interactions and Effects on Guest Thermal Stability
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2020-12-31
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Biomolecules
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Abstract
There is ongoing interest in exploiting the antioxidant activity and other medicinal properties of natural monophenolic/polyphenolic compounds, but their generally low aqueous solubility
limits their applications. Numerous studies have been undertaken to solubilize such compounds via
supramolecular derivatization with co-crystal formation with biocompatible coformer molecules and
cyclodextrin (CD) complexation being two successful approaches. In this study, eight new crystalline
products obtained by complexation between methylated cyclodextrins and the bioactive phenolic
acids (ferulic, hydroferulic, caffeic, and p-coumaric acids) were investigated using thermal analysis
(hot stage microscopy, thermogravimetry, differential scanning calorimetry) and X-ray diffraction.
All of the complexes crystallized as ternary systems containing the host CD, a phenolic acid guest,
and water. On heating each complex, the primary thermal events were dehydration and liberation
of the respective phenolic acid component, the mass loss for the latter step enabling determination
of the host-guest stoichiometry. Systematic examination of the X-ray crystal structures of the eight
complexes enabled their classification according to the extent of inclusion of each guest molecule
within the cavity of its respective CD molecule. This revealed three CD inclusion compounds with
full guest encapsulation, three with partial guest inclusion, and two that belong to the rare class of
‘non-inclusion’ compounds.
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Reference:
Hunt, L.E., Bourne, S.A. & Caira, M.R. 2020. Inclusion of Hydroxycinnamic Acids in Methylated Cyclodextrins: Host-Guest Interactions and Effects on Guest Thermal Stability. Biomolecules. 11(1) http://hdl.handle.net/11427/35243