A model for sequential threading of alpha-cyclodextrin onto a guest: a complete thermodynamic and kinetic study in water.

Détails

ID Serval
serval:BIB_89DAC4FD0FDB
Type
Article: article d'un périodique ou d'un magazine.
Collection
Publications
Titre
A model for sequential threading of alpha-cyclodextrin onto a guest: a complete thermodynamic and kinetic study in water.
Périodique
Journal of the American Chemical Society
Auteur(s)
Saudan C., Dunand F.A., Abou-Hamdan A., Bugnon P., Lye P.G., Lincoln S.F., Merbach A.E.
ISSN
0002-7863
Statut éditorial
Publié
Date de publication
2001
Peer-reviewed
Oui
Volume
123
Numéro
42
Pages
10290-10298
Langue
anglais
Résumé
The first variable-temperature and variable-pressure stopped-flow spectrophotometric study of the sequential threading of alpha-cyclodextrin (alpha-CD) onto the guest dye Mordant Orange 10, S, is reported. Complementary (1)H one-dimensional (1D) variable-temperature kinetic studies and two-dimensional (2D) rotating-frame nuclear Overhauser effect spectroscopy (ROESY) and EXSY NMR studies are also reported. In aqueous solution at 298.2 K, the first alpha-CD threads onto S to form a 1:1 complex S.alpha-CD with a forward rate constant k(1,f) = 15 200 +/- 200 M(-1) s(-1) and dethreads with a reverse rate constant k(1,r) = 4.4 +/- 0.3 s(-1). Subsequently, S.alpha-CD isomerizes to S.alpha-CD (k(3,f) = 0.158 +/- 0.006 s(-1), k(3,f) = 0.148 +/- 0.006 s(-1)). This process can be viewed as a thermodynamically controlled molecular shuttle. A second alpha-CD threads onto S.alpha-CD to form a 1:2 complex, S.(alpha-CD)(2), with k(2,f) = 98 +/- 2 M(-1) s(-1) and k(2,r) = 0.032 +/- 0.002 s(-1). A second alpha-CD also threads onto S.alpha-CD to form another 1:2 complex, S.(alpha-CD)(2), characterized by k(4,f) = 9640 +/- 1800 M(-1) s(-1) and k(4,r) = 61 +/- 6 s(-1). Direct interconvertion between S.(alpha-CD)(2) and S.(alpha-CD)(2) was not detected; instead, they interconvert by dethreading the second alpha-CD and through the isomerization equilibrium between S.alpha-CD and S.alpha-CD. The reaction volumes, DeltaV(0), were found to be negative for the first three equilibria and positive for the fourth equilibrium. For the first three forward and reverse reactions, the volumes of activation are substantially more negative, indicating a compression of the transition state in comparison with the ground states. These data were used in conjunction with DeltaH, DeltaH degrees, DeltaS, and DeltaS degrees data to deduce the dominant mechanistic threading processes, which appear to be largely controlled by changes in hydration and van der Waals interactions, and possibly by conformational changes in both S and alpha-CD. The structure of the four complexes were deduced from (1)H 2D ROESY NMR studies.
Mots-clé
Azo Compounds/chemistry, Benzene Derivatives/chemistry, Coloring Agents/chemistry, Cyclodextrins/chemistry, Kinetics, Magnetic Resonance Spectroscopy, Spectrophotometry/methods, Thermodynamics, alpha-Cyclodextrins
Pubmed
Web of science
Création de la notice
19/05/2008 11:00
Dernière modification de la notice
20/08/2019 14:48
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