Molecular engineering. Part 7. Cavitands having four aromatic sp(2) nitrogens as salt binding ligands

Nine new salt binders built on resorcin[4]arene or calix[4]arene and having four aromatic sp(2) nitrogens as salt binding ligands were designed and ch aracterized. Structurally rigid cavitands based on resorcin[4]arene showed much higher affinities toward metal cations compared to those based on flex ible calix[4]arene. In particular, imidazolylcavitand 7 showed high affinit y for alkali metal cations (-DeltaG degrees =7.0-10.9 kcal mol(-1)) and pyr azolylcavitand 8 showed unusually high selectivity for silver cations, whic h are presumably due to their different binding modes, nesting vs. inclusio n fashion, respectively.