Transduction of selective recognition by preorganized lonophores; K+ selectivity of the different 1,3-diethoxycalixarene crown ether conformers
Three different conformers of 1,3-diethoxy-p-tert-butylcalixarene crown ethers have been used to study the effect of the ionophore preorganization on the potentiometric K+-selectivity. Selectivities were measured for chemically modified field effect transistors (CHEMFETs) and membrane ion-selective electrodes (ISEs) by two different methods. The ionophores show decreasing K+/Na+ selectivities in the order: partial cone > 1.3-alternate > cone. As a function of time the cone conformer maintained a constant selectivity whereas a continuous decrease of the selectivity values was observed for the other two conformers. This supports our prediction based on the association constants and our previous 1H NMR studies on conformational stability.