Effect of conformation on metal ion extraction by calix[4]arene dicarboxylic acids

Synthetic routes to four calix[4]arene stereoisomers with two distal methoxycarboxy groups and two distal butoxy groups are reported. Conformations of cone, partial cone (butyl up), partial cone (acid up), and 1,3-alternate were established by H-1 and C-13-NMR spectroscopy. To probe the influence of ligand conformation on metal ion complexation, extractions from aqueous solutions into 1,2-dichloroethane were performed. These included competitive alkali metal cation extractions, competitive alkaline earth metal cation extractions, and single species extractions of Pb2+ and of Hg2+. Comparisons are also made with the results for a conformationally mobile analogue in which the two butoxy groups are replaced with methoxy groups.