Effect of beta-cyclodextrin charge type on the molecular recognition thermodynamics of reactions with (ferrocenylmethyl)dimethylaminium derivatives.
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.
Liu
Yu
Y
Department of Chemistry, State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, People's Republic of China. yuliu@nankai.edu.cn
Cao
Rui
R
Chen
Yong
Y
He
Jia-Yue
JY
D000465:Algorithms; D002151:Calorimetry; D005296:Ferrous Compounds / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D000075163:Metallocenes; D012997:Solvents; D021241:Spectrometry, Mass, Electrospray Ionization; D013816:Thermodynamics; D047392:beta-Cyclodextrins / Q000737:chemistry*
D005296:Ferrous Compounds; D000075163:Metallocenes; D012997:Solvents; D047392:beta-Cyclodextrins; C004998:ferrocene