A spectroscopic study of the inclusion of azulene by beta- and gamma-cyclodextrins.
The inclusion of azulene (AZ) inside the cavities of beta-cyclodextrin (beta-CD) and gamma-cyclodextrin (gamma-CD) was studied using absorption, fluorescence and induced-circular dichroism spectroscopy. The inclusion of AZ into the cavity of beta-CD has a stoichiometry of 1:1, whereas that of AZ/gamma-CD complex is 1:2. The equilibrium constants for the formation of the two complexes were calculated to be 780+/-150 M(-1) for AZ:beta-CD and (4.5+/-0.86)x10(5) M(-2) for AZ:(gamma-CD)(2). The latter is due to a stepwise equilibrium mechanism in which a 1:1 complex is formed with a binding constant of 775 M(-1), followed by the formation of a 1:2 complex with a binding constant of 580 M(-1). The difference between the two binding constant values is slight, indicating an almost equal contribution from each of the gamma-CD molecules to the overall binding in AZ:(gamma-CD)(2). From the induced-circular dichroism spectra, the inclusion of AZ was found to be axial in AZ:beta-CD and nearly axial in AZ:(gamma-CD)(2).
Abou-Zied
Osama K
OK
Department of Chemistry, Faculty of Science, Sultan Qaboos University, PO Box 36, Al-Khodh, Postal Code 123, Muscat, Sultanate of Oman. abouzied@squ.edu.om
D052176:Azulenes; D002942:Circular Dichroism; D003508:Cycloheptanes / Q000737:chemistry*; D007700:Kinetics; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D014867:Water; D047392:beta-Cyclodextrins / Q000737:chemistry*; D047408:gamma-Cyclodextrins / Q000737:chemistry*
D052176:Azulenes; D003508:Cycloheptanes; D047392:beta-Cyclodextrins; D047408:gamma-Cyclodextrins; D014867:Water; C005525:azulene; C031215:betadex