Chlorosulfonylated calix[4]arenes: precursors for neutral anion receptors with a selectivity for hydrogen sulfate

Abstract

In nature phosphate and sulfate binding proteins are very important receptors for the active transport systems in the cell.1-2 A very high selectivity in binding has been observed in prokaryotic, periplasmic phosphate and sulfate binding proteins, which demonstrate >10® selectivity for binding phosphate over sulfate and sulfate over phosphate, respectively.3 In both proteins the specific binding exclusively takes place through hydrogen bonding. Synthetic receptors that bind anions contain either positively charged guanidinium or ammonium groups4 or Lewis acid metal centers5 to accomplish anion binding. Recently we reported functionalized uranyl-containing salenes6 and sulfonamides7 derived from tris(aminoethyl)-amine (TREN) that form complexes with hard anions in CH3CN with a selectivity for H2PO4™. In the present paper we report anion receptors based on chlorosulfonylated calix[4] arenes.8 Calix[4]arenes are important building blocks in supramolecular chemistry.10-11 They can be (selectively) functionalized both at the phenolic OH groups (lower rim) and at the para positions of the phenol rings (upper rim).12