Modulation of cation binding in calix[4]arene amides: synthesis, complexation and molecular modelling studies

We report combined experimental and theoretical studies on the complexation and liquid-liquid extraction of alkali and alkaline-earth cations by a ser ies of calix[4]arenes bearing various combinations of primary, secondary an d tertiary amide substituents. Four mixed calix[4]arene amides have been sy nthesized. Upon N-alkyl to N-H substitution on the amide binding sites, the binding strength of cations is reduced in methanol, and further, the extra ction of cations from water into dichloromethane becomes highly inefficient . However, high complexation selectivities for Sr2+ and Ca2+ over Na+ are a chieved for a mixed primary/tertiary derivative. The structures of typical free and complexed ligands are elucidated by NMR analysis and by molecular dynamics simulations in methanol and chloroform solution. Simulations at th e water/organic interface also reveal different behaviour of tertiary/secon dary/primary amide complexes.