KINETIC AND EQUILIBRIUM STUDIES OF CYCLOMALTO-OCTAOSE (γ-CYCLODEXTRIN)-METHYL ORANGE INCLUSION COMPLEXES

Article abstract of DOI:10.1016/0008-6215(84)85352-5

Measurements of the equilibrium and temperature-jump u.v., visible, and induced c.d. spectra of Methyl Orange (MO) in the presence of cyclomalto-octaose (γ-cyclodextrin, γ-CD) have been carried out.Three mechanistic steps were detected through the temperature-jump data (25.0 deg): MO + γ-CD <*> MO.γ-CD fast (K1), MO + MO.γ-CD <*> (MO)2.γ-CD slow (K2), and γ-CD + (MO)2.γ-CD + (MO)2.γ-CD ^->_<- (MO)2.(γ-CD)2 fast (K3), where K₁, K₂, and K₃ are 45 (+/-7), 2.0 (+/-1.1) x 1E6, and 6.1 (+/-2.5) x 1E3 dm³.mol^-1, respectively, k₂ = 9.4 (+/-5.1) x 1E9 dm3.mol^-1.s^-1, and k_-2 =4.8 (+/-0.8) x 1E3 s^-1.The equilibrium u.v./visible data are also consistent with this reaction scheme.The high stability of the dimer inclusion complex (MO)2.γ-CD compared to that of the monomer inclusion complex MO.γ-CD appears to be related to the annular diameter of γ-CD and demonstrates a degree of selectivity in cyclodextrin inclusion complexes.The (MO)2.(γ-CD)2 complex also contains a dimer, included by both γ-CD molecules.