European Journal of Organic Chemistry, issue 35 (2008) pp. 5891-5898
A combined NMR, computational, and HPLC study of the inclusion of aromatic and fluoroaromatic compounds in cyclodextrins has been carried out with the aim of studying this process as a model for carbohydrate···aromatic interac- tions. NMR experiments showed that although β-CD formed an inclusion complex with benzene, no stable inclusion ad- duct was formed with hexafluorobenzene. MM3* calcula- tions confirmed these data and, when extended to naphtha- lene, anthracene, phenanthrene, and their partially and fully fluorinated analogues, showed that β-CD formed inclusion adducts only with the hydrocarbons, whereas the partially fluorinated derivatives were shown to enter the cavity only with their non-fluorinated part, and the perfluoro compounds were not included. HPLC experiments, carried out by eluting these compounds through CD-modified HPLC columns, also confirmed these results, at least with the mono- and bicyclic arenes. Indeed, the elution of these derivatives showed that the efficiency of the inclusion, as determined by comparing HPLC retention times, decreased on passing from hydro- carbons to partially fluorinated compounds, and reached a minimum with perfluorinated derivatives. In contrast with this general trend, 1,2,3,4-tetrafluoroanthracene had longer retentions times on β- and γ-CD-modified HPLC columns than anthracene, possibly for solubility reasons. As a whole, these results were interpreted in terms of carbo- hydrate···aromatic interactions between the C5–H5 bonds on the hydrophobic faces of the sugars and the π electrons of the aromatic partner. The interactions seem to have an important dispersive component.
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