Alison Skelley - University of Alberta

Placement: University of Victoria
Supervisor: Dr. Cornelia Bohne

Investigation of the Dynamics of Xanthone and Xanthone Derivatives in Cyclodextrins

In an attempt to find a probe with photophysics like those exhibited by xanthone, the molecule 4mpx was studied. It behaved in a similar fashion to xanthone, in that when complexed to cyclodextrins (b- and g-) the intensity of fluorescence decreased. From that information, the equilibrium constants for complexation could be calculated. Laser flash photolysis studies indicate that 4mpx is also sensitive to its environment, meaning that its triplet state exhibits a shift in absorption maximum depending on polarity. However, it was found to be a light sensitive compound and, unlike xanthone, the equlibrium constant for the formation of the b-cyclodextrin complex decreased over time. When complexed with the larger g-cyclodextrin, the equlibrium constant remained steady as did that of xanthone, so perhaps the size of the cavity is preventing the 4mpx molecule from entering the bucket easily. This theory was also supported by Induced Circular Dichroism, in which the spectra of xanthone and 4mpx contained maxima at different wavelengths, suggesting that the molecules were in diffferent locations within the b-cyclodextrin host. Finally, using a quenching methodology the k_association and k_dissociation could be calculated. 4mpx was found to have a k_association about 10 times faster than that of xanthone, again implying that the molecule is somehow not sitting as expected inside the host. Further studies to be done include a time dependance for the ICD to see if the spectral maxima shift when the 4mpx/b-cyclodextrin solution is allowed to sit, and further quenching studies to establish that the preliminary results are correct and to see if the two k's change over time.