Complexation of p‐Sulfonatocalixarenes with Local Anaesthetics Guests: Binding Structures, Stabilities, and Thermodynamic Origins

The binding geometries, abilities and thermodynamic parameters for the intermolecular complexation of three water‐soluble p ‐sulfonatocalix[ n ]arenes ( SC n A s), p ‐sulfonatocalix[4]arene ( SC4A ), p ‐sulfonatocalix[5]arene ( SC5A ), and p ‐sulfonatothiacalix[4]arene ( STC4A ), with five local anesthetics ( LA ), procaine, tetracaine, lidocaine, dibucaine, and procainamide, have been determined by means of 1 H NMR spectroscopy, X‐ray crystallography, and isothermal titration calorimetry (ITC). The obtained results show that the complexation of SC n A s with LA guests shows unappreciable guest selectivity, but regular host selectivity: SC4A > SC5A > STC4A for each guest. A large difference in the enthalpy term is responsible for the decrease in the stability constants. The intrinsic relationship between binding structures and host selectivities were comprehensively analyzed and discussed from the viewpoint of thermodynamics. Furthermore, the complexation of SC4A towards LA guests were compared with other macrocyclic hosts, β‐cyclodextrin and cucurbit[7]uril.