engleski

Solvation effect on the complexation of adamanthyl glycoside with beta- cyclodextrins

(S)-N-(adamant-1-yl)-3-(β-D- mannopyranosyloxy)-2-methylpropanamide, was prepared by condensation of 1- adamantamine and mannose through short linker. The complexation thermodynamics of this compound with β-cyclodextrin and 6-O- monotosyl-β-cyclodextrin in water, methanol, ethylene glycol, formamide, and N-methylformamide was explored by means of microcalorimetry and NMR spectroscopy. The complex formation was observed in water, ethylene glycol and formamide. The temperature dependence (5 ≤ θ / ºC ≤ 65) of standard thermodynamic complexation parameters in these solvents was studied in detail. The structures of reaction products were investigated by means of NMR spectroscopy. The stabilities of the complexes were highest in water followed by formamide and ethylene glycol, whereby all reactions were enthalpically controlled at temperatures examined. The ΔrHº values for complexation reactions in formamide and ethylene glycol were rather similar in the studied temperature range, whereas the corresponding values in water decreased with the increase in temperature. The reaction entropies in all examined solvents were less favourable at higher than at lower temperatures. The stability constant of the synthetic macrocycle and adamantyl mannoside complex was lower than that with β-cyclodextrin. The main driving force for the formation of complexes can be attributed to solvophobic solvation of the host cavity and the adamantane subunit. The differences in the temperature dependence of the complex stabilities in water and both formamide and ethylene glycol can be explained by more pronounced changes of water structure with change in temperature.

adamantane ; β-cyclodextrin ; complexation ; solvation

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