Exploitation of Na⁺-selective electrodes for protein solutions from crown-bridged calix[4]quinones

Crown-bridged calix[4]quinones (5 and 6) were synthesized from calix[4]crown (2). The ion-selective electrodes prepared from 5 or 6 still retained high selectivity for Na⁺ against K⁺ (>10³). For protein solution samples the electrode prepared from 2 showed a large phase divergence whereas those prepared from 5 or 6 were much more stable in protein solution. The difference is attributed to the less hydrophobic nature of 5 and 6 which strongly influences the protein adsorption onto the membrane surface.