Influence of the substitution of β-cyclodextrins by pyridinium groups on the complexation of adamantane derivatives
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A series of positively charged β-cyclodextrin derivatives have been synthesized by selective functionalization of β-cyclodextrin at the primary rim with pyridinium groups. Characterisation of the modified β-cyclodextrin was done by elementary analysis, FTIR, 1H and 13C NMR spectroscopy. The inclusion complexation of adamantane derivatives (Adamantan-1-ol: AdOH and Sodium adamantane-1-carboxylate: AdCOO−Na+) by the host β-cyclodextrin and its grafted pyridinium derivatives has been investigated using 1H NMR spectroscopy. The stoichiometry of the complexes was found to be in 1:1 (adamantane:β-cyclodextrin) ratio. 1H chemical shift changes of adamantane protons were used to calculate the apparent binding constants of the complexes. Two dimentional NOESY experiments were performed to allow the mode of binding. Mono- and per-charged β-cyclodextrin showed an enhancement of inclusion binding ability towards the sodium adamantane-1-carboxylate guest. The origin of the observed enhancement in the stability of the complexes was ascribed to electrostatic interaction between carboxylate ion and charged pyridinium groups. A simple thermodynamic model of the electrostatic contribution to the complexation is presented.
KeywordsPyridinium-β-cyclodextrins Adamantane derivatives Inclusion complexes 1H NMR Apparent binding constant
This work was supported by a Grant from French–Tunisian cooperation project (CMCU n°04S1207).
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