Photocontrolled binding of artemisinin to a bis(beta-cyclodextrin) bearing azobenzene on the primary face

Circular dichroism titrations with multivariate global analysis of multiwavelength data have been used to study the binding behavior of 4,4'-bis(6'-O-cyclomaltoheptaosyl)azobenzene (CyD2-AB). This host system in the trans configuration, 10-4 M in neutral aqueous solution, is able to form a 1:1 complex with artemisinin (ART) with log (K11/M-1) = 4.1 ± 0.1, at 22 °C. Photoirradiation at 363 nm switches the linker from the trans to the cis configuration and the latter shows a loss of interaction with ART. The difference in the binding features between the two geometrical isomers of CyD2-AB suggests light control is possible for ART binding in aqueous solution through the photoisomerization reaction. The binding behavior of this host depends on its concentration. At 10-3 M trans CyD2-AB forms a complex with ART characterized by a 2:1 host:guest stoichiometry and log (K21/M-2) = 6.7 ± 0.3 .