Ion transport activity of calix[n]arene (n=4, 5, 6, 7, 8) esters toward alkali-metal cations in a phospholipid bilayer membrane

Abstract

Alkali-metal ion transport by a series of p-tert-butylcalix[n]arene (n=4, 5, 6, 7, 8) esters (1–5) across a soybean phospholipid bilayer membrane has been investigated by a voltage clamp method. The measurement of electric currents resulting from ion transport across the phospholipid bilayer shows that esters 1–4, show ion transport ability but that 5 does not. From an analysis of current–voltage curves, the values of ion permeability across the bilayer are determined for 1–4. The ion permeability of Na⁺ by 1 is >20 times that of other alkali-metal ions, suggesting that 1 acts as a selective Na⁺ carrier in phospholipid bilayer membranes. 2 transports K⁺ better than Na⁺, while the ion transport selectivity of 2 is poor compared to that of 1. Both 3 and 4 shows Cs⁺ transport selectivity. The transport selectivity (Cs⁺/Rb⁺) of 3 is better than that of 4 by a factor of 2.