Double Uphill Transport of Ca2+−Na+ or Ca2+−K+ in Opposite Directions by Lipophilic Crown Ethers with Two Carboxylic Acid Moieties

A variety of lipophilic crown ethers containing two carboxylic acid moieties were prepared, and their transport abilities were estimated in the double uphill transport system of Ca2+−Na+ or Ca2+−K+ by pH control through a bulk liquid membrane using dichloromethane. As expected, 15-crown-5 and 18-crown-6 derivatives were found to be effective for Ca2+−Na+ and Ca2+−K+ exchange systems, respectively. As a result, the calcium ion was concentrated in the acidic phase, and the sodium ion or potassium ion was concentrated in the other phase. In addition to the structure of the carriers, a proper selection of the transport conditions was one of the crucial factors for realizing this double uphill transport system. A simple combination of the active transporter of the calcium ion and the passive carrier for the sodium ion was also found to enable the exchange between the calcium and sodium ions against their concentration gradients. When two ionophores effective for Ca2+−K+ and K+−Na+ exchange systems, respectively, were used at the same time, the calcium and potassium ions were concentrated in the acidic phase, whereas the sodium ion was concentrated in the basic phase.