Pressure Effects on the Binding of 1,4-Dioxane to Amide Naphthotubes in Water

Abstract

Host-guest interactions between a pair of naphthalene-based molecular tubes (i.e., anti-isomer and syn-isomer) and 1,4-dioxiane have been studied to understand selective recognition. Volume changes for complexation of the amide naphthotubes with 1,4-dioxane were investigated using high-pressure fluorescence and high-pressure NMR spectroscopy. We found that the partial molar volume change (ΔV°) for the association of 1,4-dioxane with the naphthotubes was －6.3±0.1 mL mol^－1 for the anti-isomer and 3.2±0.4 mL mol^－1 for the syn-isomer. To elucidate the molecular basis of ΔV°, molecular dynamics simulations of the complexation process were also performed. The difference in ΔV° was attributed to variations in the shape and hydration of naphthotube hydrophobic cavities.