Calix[4]arene sulfonate hosts selectively modified on the upper rim: a study of nicotine binding strength and geometry

We present the synthesis and structure-activity relationships of sulfonatocalix[4]arene hosts bearing novel substitutions. The calix[4]arenes are modified on upper rim at either one or two phenolic units, where dual modifications introduced regioselectively neighbouring opposing phenols. mono- di-functionalised with nitro formyl groups, remaining upper-rim sites in all cases occupied by sulphonates. Equilibrium association constants were determined between each host guests nicotine, nornicotine, cotinine. Indicator displacement-based binding studies show that nicotine binds most strongly to different members library followed whereas cotinine displays weak no binding. NMR titrations carried out host-guest interaction geometries for formyl-calix[4]arenes versus nitro-calix[4]arenes.