1H NMR and Calorimetric Studies of the Inclusion of Trimethylammonium Cations into Water Soluble Calixresorcinarenes

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Abstract
The complexation of tetramethylammonium (TEMA), benzyltrimethylammonium (BTMA), p-nitrobenzyltrimethylammonium (BTMAN) and N, N, N-trimethylanilinium (TMA) by the tetrasulphonate derivative of the resorcinol cyclic tetramer (1), was studied in aqueous solution by 1H NMR and calorimetry. Host 1 specifically recognizes the—N+ (CH3)3 group of TEMA, BTMA and BTMAN, whereas it binds TMA unselectively; TMA is included both via the charged group and the aromatic moiety. The binding constants of all four guests with 1, as determined by both 1H NMR and calorimetric titrations, show that all inclusion processes are almost equally stabilised. ΔHΔ and ΔSΔ values, determined by direct calorimetry, reveal specific interactions that are not expressed in the ΔGΔ terms and indicate that we are dealing with “non-classical hydrophobic effects”. The effects of the structural, conformational and electronic properties of the guests on the forces driving the inclusion processes are discussed.

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