engleski

Hydrophobic cavities and diamantanes

Diamantane derivatives are excellent guests for cucurbit[7]uril (CB7), forming complexes with stability constants reaching above petamolar values in water. However, their inclusion within hydrophobic cavities was rarely explored in non- aqueous solutions. We have therefore studied the solvent (water, formamide, ethylene glycol) and temperature effects on the complexation of diamantane alcohols with CB7 and β- and γ- cyclodextrin by means of isothermal microcalorimetry and NMR spectroscopy. Complex stability constants were much higher in water due to less unfavorable ΔrS°. The reactions involving apical alcohols were the most exergonic. A significant temperature dependence of ΔrH° and ΔrS° resulted in an almost perfect enthalpy- entropy compensation for most of the studied host- guest systems. The thermodynamic complexation parameters were in agreement with the classical rationale of the hydrophobic effect at lower temperatures and non-classical explanation at higher ones. The results of 1H NMR titrations were in accord with the thermodynamic studies and have revealed an interesting difference in complex formation kinetics between cucurbit[7]uril and β- cyclodextrin hosts.

cucurbit[7]uril ; cyclodextrins ; diamondoid alcohols ; host-guest complexes ; microcalorimetry ; solvophobic effect

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