engleski

(A) Romantic Relationship Between Hydrophobic Cavities and Aromatic Alcohols

β-cyclodextrin and cucurbit[7]uril are known to be very good receptors for adamantane-like guests in water, due to their perfect fit within the mentioned cavities. By contrast, the hosting of aromatic guests was far less frequently explored. The influence of various substituents on benzene inclusion remained almost unknown. Likewise, the binding thermodynamics of aromatic and structurally similar aliphatic guests was never systematically compared. We therefore studied the complexation of various aromatic alcohols and their hydrogenated analogues with cucurbit[7]uril and β-cyclodextrin in water using several experimental techniques (isothermal titration microcalorimetry, fluorimetry, spectrophotometry and NMR spectroscopy). Considerable substituent impact on the complex stability was observed in the case of p-substituted phenols which can be explained by differences in electron density distributions of the hosts and guests. Substantial influence of guest aromaticity on complexation thermodynamics was observed in experiments with hydrogenated derivatives of 2-naphthol. The reactions involving the aliphatic guest were far more entropically favourable, leading to higher stability constants compared to complexes with aromatic analogues. For most of the examined host-guest systems an enthalpy-entropy compensation was observed, resulting in weak temperature dependence of ΔrG°. The complexation thermodynamics was in agreement with the classical interpretation of the hydrophobic effect at lower temperatures and the non-classical explanation at higher ones.

Hydrophobic effect ; inclusion complex ; complexation thermodynamics ; cyclodextrins ; cucurbit[7]uril ; aromatic alcohols

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