Complexation of carboxylic acids and anions by alpha and beta cyclodextrins |
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Authors: | Robert I Gelb Lowell M Schwartz |
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Institution: | (1) Department of Chemistry, University of Massachusetts, 02125 Boston, MA, USA |
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Abstract: | A pH potentiometric method is used to measure complex formation constants of aqueous alpha- and/or beta-cyclodextrin with several carboxylic acids and carboxylate anions: butyric acid/butyrate; valeric acid/valerate; hexanoic acid/hexanoate; octanoic acid/octanoate; decanoic acid/decanoate; cyclohexanecarboxylic acid/cyclohexanecarboxylate and benzoic acid/benzoate. Standard enthalpies and entropies of complex formation are calculated from the temperature dependencies of the equilibrium constants. These thermodynamic parameters of the alpha-cyclodextrin complexes largely conform to a correlation based on complexes with other substrate species previously reported. Both standard enthalpies and entropies of formation of beta-cyclodextrin complexes are found to be more positive than the corresponding complexes of alpha-cyclodextrin with the same substrates. These observations lead to insights into the bonding mechanism of cyclodextrin complexation. |
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Keywords: | Cyclodextrin formation constant carboxylic acid guests |
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