A water-soluble phosphate-footed cavitand : synthesis and binding properties with small neutral organic molecules

• Main Author: Gui, Xuan
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/10642

This thesis presents a study of apolar host-guest complexations between a bowl-shaped cavitand host and small neutral organic guest molecules in aqueous solutions. The watersoluble host molecule-cavitand 1, with methyl groups on the rim positions and hydrophilic phosphate groups at the pendent positions, was synthesized. It forms 1:1 host-guest complexes in aqueous solutions exclusively with most investigated guest molecules. Binding constants of these complexes were determined from ¹H NMR titration experiments. The strongest bindings were found between host 1 and small ester guest molecules. Variable temperature NMR titration experiment uncovered that binding processes were driven by favorable enthalpy changes accompanied with unfavorable entropy changes. These results were discussed in terms of the attractive van der Waals interactions between host and guest as well as the hydrophobic effect. The geometry of the complexes in aqueous solution was elucidated by ¹H NMR spectroscopy and molecular mechanics calculations. For guests containing two potential binding sites, they form isomeric complexes with host 1.