Selective binding and highly sensitive fluorescent sensor of palmatine and dehydrocorydaline alkaloids by cucurbit[7]uril

The complexation behavior of palmatine (P) and dehydrocorydaline (DHC) alkaloid guest molecules by cucurbit[7]uril (CB7) host have been investigated by means of fluorescence spectra in aqueous phosphate buffer solution (pH 7.2). It is found that each alkaloid exhibits dramatic fluorescence enhancement upon complexation with CB7, and the intensity of the emittance is strong enough to be readily distinguished by the naked eye. Although the two guests possess similar structure, the complex stability constant of P with CB7 is 5.4 times larger than that of DHC. 1H NMR studies show that the binding modes differ much, i.e., deep encapsulation for P-CB7 and shallow encapsulation for DHC-CB7. Furthermore, the solvent effects and salt effects during the course of complexation have also been investigated, showing they significantly influence the binding ability and selectivity of CB7 with the alkaloid guests. Particularly, addition of a small amount (4 vol%) of ethanol increases the P/DHC selectivity to 17.2.