Complexation of methylammonium salts and sugar-related alcohols with resorcinol cyclic tetramer in water: An implication of the CH-π interaction on polar guest binding

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Abstract
Methylammonium cations and sugar-related alcohols are bound to the tetrasulphonate derivatives 1a-1c of the resorcinol cyclic tetramer in water. With respect to the change in substituent X on C-2 of the benzene rings of the host, both 1b (X = CH3, highly hydrophobic and moderately electron-donating) and 1c (X = OH, highly hydrophilic and highly electron-donating) exhibit higher binding abilities than the parent host 1a (X = H). These results suggest that the CH-π interaction, involving polarized C-H bonds of the guest and electron-rich benzene rings of the host, makes a substantial contribution to the guest-binding process. Host 1c even binds more hydrophilic dioxygen-functionalized sugar models (cis-1,2-cyclohexanediol, 2-oxacyclohexyl-1-carbinol and 2-oxacyclopentyl-1-carbinol) more strongly than the corresponding more hydrophobic mono-ols (cyclohexanol, cyclohexylcarbinol and cyclopentylcarbinol).