Complexation of adamantane-ammonium substrates by beta-cyclodextrin and itsO-methylated derivatives
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A spectrophotometric method is used to determine formation constants of complexes ofβ-cyclodextrin, the 2,6-di-O-methylated and 2,3,6-tri-O-methylated derivatives ofβ-cyclodextrin as hosts with adamantan-1-ylammonium, adamantan-2-ylammonium and adamantan-1-ylmethylammonium as substrate species. The spectrophotometric method uses methyl orange anion and acid forms as indicator species. Complexes of the cyclodextrins with these species are determined as well as with the adamantane derivatives. Standard enthalpies and entropies of formation of all complexes are calculated from the temperature variation of the equilibrium constants.β-Cyclodextrin and its 2,6-O-methyl derivative have comparable complex strengths with adamantaneammonium substrates and these strengths are about two orders of magnitude stronger than the corresponding complexes of the permethylated derivative. Thermodynamic parameters are interpreted in terms of differing intramolecular properties of the cyclodextrin complexes.
Key wordsCyclodextrin formation constant uv-visible spectrophotometry cationic guests
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