Kinetic and equilibrium studies of cyclomalto-octaose (γ-cyclodextrin)-methyl orange inclusion complexes

✍ Scribed by Ronald J. Clarke; John H. Coates; Stephen F. Lincoln

• Publisher: Elsevier Science
• Year: 1984
• Tongue: English
• Weight: 667 KB
• Volume: 127
• Category: Article
• ISSN: 0008-6215
• DOI: 10.1016/0008-6215(84)85352-5

✦ Synopsis

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 (y-cyclodextrin, r-CD) have been carried out. Three mechanistic steps were detected through the temperature-jump data (25.0"): MO + y-CD = MO e y-CD fast WI), MO + MO . y-CD 2 (MO), . y-CD k-z slow (&), and y-CD + (MO)* * y-CD = (MO), * (y-CD), fast (&),

where K,, K2, and K3 are 45 (f7), 2.0 (fl.1) X 106, and 6.1 (f2.5) X lo3 dm3.mol-I, respectively, k2 = 9.4 (f5.1) x lo9 dm3.mol-1.s-1, and k_* = 4.8 (kO.8) X103 s-l. The equilibrium u.v./visible data are also consistent with this reaction scheme. The high stability of the dimer inclusion complex (MO), * y-CD compared to that of the monomer inclusion complex MO . y-CD appears to be related to the annular diameter of y-CD and demonstrates a degree of selectivity in cyclodextrin inclusion complexes. The (MO), * (Y-CD)~ complex also contains a dimer , included by both y-CD molecules.