Molecular Recognition Study on Supramolecular System. 14.1 Synthesis of Modified Cyclodextrins and Their Inclusion Complexation Thermodynamics with L-Tryptophan and Some Naphthalene Derivatives

Document Type

Article

Publication Date

3-6-1998

Abstract

A series of β-cyclodextrin derivatives, carrying pyridinio (4-6), phosphonyl (7, 8), seleno (9-11), m- and p-picolinyl (12, 13), o-chloroanilino (16), 8-quinolyl (17), furfuryl (18), and 9-fluorenyl (19) moieties in the side chain, were newly synthesized, and their complexation behavior was assessed and discussed thermodynamically, using L-tryptophan and a few naphthalene derivatives as representative guests. Calorimetric titrations have been performed at 25.0°C in buffered aqueous solution (pH 7.20) to give the complex stability constants and thermodynamic parameters for the 1:1 inclusion complexation of these guests with the native and modified α-, β-, and/or γ-cyclodextrins (1-20). All of the chemical modifications to the primary side of cyclodextrins examined led to significant changes in complex stability and thermodynamic parameters, which are elucidated in terms of the conformational, electrostatic, hydrogen-bonding, and hydration effects. Thermodynamically, the inclusion complexation is mainly enthalpy-driven with a negative or minor positive entropic contribution, which in some cases determines the complex stability. The induced circular dichroism spectral analyses of these cyclodextrin derivatives indicated that the aromatic moiety in modified β-cyclodextrins (4-6, 9-19) only shallowly penetrates into the hydrophobic cavity of β-cyclodextrin, while the phenyl phosphate and fluorenyl moieties in 7 and 20 are embedded into the hydrophobic cavity of β-cyclodextrin because of the longer linking chain. Using all the thermodynamic data for a wide variety of cyclodextrin derivatives obtained in this and previous studies, the entropy changes (TΔS) were plotted against the enthalpy changes (ΔH) to give an excellent linear relationship. The slope (α) of 1.02 and an intercept (TΔS0) of 4.3 of the regression line indicate substantial conformational changes and extensive desolvation caused upon complexation, respectively.

Publication Source (Journal or Book title)

Journal of Organic Chemistry

First Page

1444

Last Page

1454

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