engleski

Hydrophobic effect – comparison of aromatic and aliphatic alcohols

Derivatives of adamantane and similar rigid aliphatic structures are known as suitable guests for cyclodextrins and cucurbit[7]uril in water. While hosting of aliphatic compounds was frequently explored, the inclusion of aromatic functionalities within cyclodextrins and cucurbiturils is far less investigated. Furthermore, the binding thermodynamics of aromatic and structurally similar aliphatic guests was never systematically compared. Therefore, the complexation of 2-naphthol and its hydrogenated analogues with cucurbit[7]uril and cyclodextrins in water was explored by means of isothermal titration microcalorimetry, fluorimetry, spectrophotometry, and NMR spectroscopy. Significant influence of guest aromaticity on complexation thermodynamics was observed – the reactions involving aliphatic guest were remarkably more entropically favourable, leading to higher complex stability constants compared to the ones with aromatic analogues. Reaction enthalpy and entropy of the majority of examined systems varied substantially with temperature, resulting in nearly complete enthalpy-entropy compensation (weak temperature dependence of ΔrG°). The complexation thermodynamics at lower temperatures was in agreement with the classical interpretation of the hydrophobic effect, while the binding at higher temperatures could be rationalized by the non-classical rationale.

2-naphthol derivatives ; complexation thermodynamics ; cucurbit[7]uril ; cyclodextrins ; hydrophobic effect ; inclusion complex

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