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Facile dimerization of viologen radical cations covalently bonded to β-cyclodextrin and suppression of the dimerization by β-cyclodextrin and amphiphiles

Title
Facile dimerization of viologen radical cations covalently bonded to β-cyclodextrin and suppression of the dimerization by β-cyclodextrin and amphiphiles
Authors
Park J.W.Choi N.H.Kim J.H.
Ewha Authors
박준우
SCOPUS Author ID
박준우scopusscopus
Issue Date
1996
Journal Title
Journal of Physical Chemistry
ISSN
0022-3654JCR Link
Citation
Journal of Physical Chemistry vol. 100, no. 2, pp. 769 - 774
Indexed
SCOPUS scopus
Document Type
Article
Abstract
Dimerization of radical cations of mono-6-(1-alkyl-4,4′-bipyridino)-β-cyclodextrins (β-CD-CnV•+, n = 6, 7, 8) formed via Ru(bpy)32+-sensitized photochemical reduction of β-CD-CnV2+ was studied spectroscopically, and the results were compared with those of methylalkyl viologens. Spectral characteristics of monomer and dimer of viologen radical cations were derived. The dimerization constants have been determined to be 4.0 × 104 M-1 for β-CD-C6V•+, 8.9 × 105 M-1 for β-CD-C7V•+, and 6.8 × 106 M-1 for β-CD-C8V•+. These values are 2-3 orders of magnitude greater than those for the corresponding methylalkyl viologen radical cations. The dimer formation is driven by a large enthalpy decrease and a moderate entropy increase. The dimerization is suppressed upon addition of β-CD or amphiphilic molecules that are included into β-CD. These results indicate that the dimers are stabilized by inclusion of the alkyl chain of the 1-alkyl-4,4′-bipyridino moiety of the β-CD-CnV•+ molecule into the β-CD cavity of the counter molecule. Association constants of β-CD-CnV•+ with β-CD and amphiphilic molecules have been determined from the dependence of dimerization constants on the concentrations of β-CD or amphiphiles. The results suggested that the terminal methyl and ethyl groups of the alkyl chains of β-CD-C7V•+ and β-CD-C8V•+, respectively, are included in the β-CD cavities of the same molecules, and this intramolecular inclusion affects the association of β-CD-CnV•+ with β-CD and amphiphiles. © 1996 American Chemical Society.
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자연과학대학 > 화학·나노과학전공 > Journal papers
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