Membrane electrodes and optodes performing allosteric recognition of ions

Abstract

New polyvinyl chloride (PVC) membrane electrodes which show allosteric ion recognition between F- and Na+ were proposed and fabricated. The membranes incorporating phenylboronic acid as a precursor for anionic sites, F- as an effector to generate anionic site and NaX ionophore as a receptor for Na+ ions in DOS-plasticized PVC were fabricated. The study was initially relied on optode experiments. The optode membrane was prepared to study the interaction of phenylboronic acid and F- in the membrane phase using UV-Vis spectroscopy. The result showed that phenylboronic could form complex with F-, and the membrane responded to F- at concentration as low as 10-8 M. Moreover, potentiometry was used to ¬study the response of the membrane towards Na+. DOS-plasticized PVC membranes containing p-tert-butylcalix[4]arene-tetraacetic acid tetraethyl ester (NaX) and 4-[(4-tert-butyl-2-methylphenoxy)methyl]phenylboronic acid (50% mol compared to NaX) were found to give the best characteristic of Na-ISEs upon conditioning the membranes in 10-2 M NaF: a response slope of 57.48 mV per decade and detection limit of 7.42×10-7 M. Potentiometric responses of Na-ISEs were found to depend largely on membrane resistances (Rm) varied with concentrations of fluoride ions used in membrane conditioning steps. Electrochemical impedance spectra showed a linear relationship between Rm and concentration range of NaF (1×10-1–1×10-8 M). Conditioning optimal membranes with various concentrations of Bu4NF gave a non-linear relationship. The proposed allosteric membrane electrode, thus, showed permselectivity toward Na+ using F- as an effector. The results can be potentially used for detection of low concentration of F- in aqueous solution.