Membrane transport systems. I. Synthesis and characterization of carriers for a proton driven alkali metal cation pump

The synthesis of a series of macrocyclic polyethers (crown ethers) of interest as carriers for the countertransport of metal ions and protons across artificial membranes is described. Thallium mediated cyclization of oligoethyleneglycol diiodides with (+)–N,N,-N′,N′-tetramethyltartaramide gave 15-crown-5 and 18-crown-6 diamides which were converted, via the diacids and anhydrides, to crown ether monoamides bearing long chain alkyl groups (octyl, tetradecyl, and octadecyl). The alkali metal salts and complexes of these carriers are soluble in nonpolar solvents and alkali metal ions are extracted from aqueous solutions into chloroform solutions of the carriers. Acidity constants and stability constants for complex formation in methanol/water (90:10 v/v) solutions have been determined using a combination of ion selective electrode and pH-metric techniques. Deprotonation of the ligand carboxylic acid group results not only in more stable complexes but also more selective complexation. Implications for membrane transport are discussed.