Substituent effects on the binding of phenols to cyclodextrins in aqueous solution

Journal Article · Thu Sep 07 00:00:00 EDT 1989 · Journal of Physical Chemistry; (USA)

DOI:https://doi.org/10.1021/j100355a057· OSTI ID:7246585

Bertrand, G L; Faulkner, Jr, J R; Han, S M; Armstrong, D W ^[1]

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1. Univ. of Missouri, Rolla (USA)

Equilibrium constants and standard enthalpies have been measures calorimetrically for the formation of complexes of {alpha}- and {beta}-cyclodextrins with substituted phenols in aqueous solutions at 298.15 K. The study includes variation of the size and shape of the phenol, the size and degree of methylation of the cyclodextrin, and the effects of pH and ionic strength. Substituent effects were measured for p-chloro-, p-bromo-, p-methyl-, p-hydroxy-, p-nitro- and m-nitrophenols. The effects of ionization were studied with m- and p-nitrophenolate ions. The effects of methyl substitutions of {beta}-cyclodextrin were investigated with nitrophenol and nitrophenolate ions complexing with heptakis (2,6-di-O-methyl)-{beta}-cyclodextrin and heptakis (2,3,6-tri-O-methyl)-{beta}-cyclodextrin. All of the effects studied show a substantial amount of entropic-enthalpic compensation, such that free energy effects are relatively small in comparison to enthalpic and/or entropic effects, but there was no simple relationship between the standard enthalpies and entropies of complex formation. However, a linear relationship was observed between the enthalpy and entropy for the transfer of substituted phenols from the complex with {alpha}-cyclodextrin to the complex with {beta}-cyclodextrin. This relationship was independent of pH and ionic strength. In general, complex formation of a substituted phenol with {alpha}-cyclodextrin is more exothermic than with {beta}-cyclodextrin, but the entropy of complex formation is also more negative.

• DOE Contract Number: FG02-88ER13819
• OSTI ID: 7246585
• Journal Information: Journal of Physical Chemistry; (USA), Journal Name: Journal of Physical Chemistry; (USA) Vol. 93:18; ISSN 0022-3654; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400000* -- Chemistry
400200 -- Inorganic
Organic
& Physical Chemistry
AQUEOUS SOLUTIONS
AROMATICS
CALORIMETRY
CARBOHYDRATES
CHEMICAL REACTIONS
DATA
DEXTRIN
DISPERSIONS
ENTHALPY
EXPERIMENTAL DATA
HYDROXY COMPOUNDS
INFORMATION
MEASURING INSTRUMENTS
MEASURING METHODS
MIXTURES
NUMERICAL DATA
ORGANIC COMPOUNDS
PHENOLS
PHYSICAL PROPERTIES
POLYSACCHARIDES
SACCHARIDES
SOLUTIONS
THERMODYNAMIC PROPERTIES