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J Phys Chem B. 2008 Feb 7;112(5):1445-50. doi: 10.1021/jp0760206. Epub 2008 Jan 15.

Effect of beta-cyclodextrin charge type on the molecular recognition thermodynamics of reactions with (ferrocenylmethyl)dimethylaminium derivatives.

Author information

1
Department of Chemistry, State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, People's Republic of China. yuliu@nankai.edu.cn

Abstract

Complex stability constants (KS), standard molar enthalpic changes (DeltaH degrees ), and entropic changes (TDeltaS degrees ) for the inclusion complexations of native beta-cyclodextrin (1) and two oppositely charged beta-cyclodextrins, i.e., mono(6-amino-6-deoxy)- beta-cyclodextrin (2) and mono[6-O-6-(4-carboxylphenyl)]- beta-cyclodextrin (3), with two (ferrocenylmethyl)dimethylaminium derivatives, i.e., FC4+Br(-) and FC8+Br(-), were determined at 25 degrees C in aqueous phosphate buffer solution (pH 7.20) by means of isothermal titration microcalorimetry (ITC). Cyclic voltammetry studies showed that the ferrocene groups of the guests were included in the beta-cyclodextrin cavity to form host-guest complexes. As compared with neutral beta-cyclodextrin, the positively charged host 2 showed decreased binding toward (ferrocenylmethyl)dimethylaminium guests. This was attributed to electrostatic repulsion, while the negatively charged host 3 displayed increased binding due to electrostatic attractions. Thermodynamically, the ionization of host CDs affects both enthalpic and entropic changes of host-guest complexations presumably by changing the hydrophobicity and the desolvation effect of hosts upon inclusion complexation. Moreover, the solvent effect was also discussed from the viewpoint of thermodynamics.

PMID:
18193857
DOI:
10.1021/jp0760206
[Indexed for MEDLINE]

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