Development and application of high-performance ion-selective electrodes

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The development and application of ion-selective electrodes continue to be an area of focus. In this study, we developed organic ammonium ion-selective electrodes by modifying the upper rim of calix[6]arene.hexaacetic acid hexaethyl ester with various alkyl substituents. We found that the substitution of bulkier alkyl groups enabled a more effective discrimination of simple aliphatic ammonium ions such as methylammonium and ethylammonium. In particular, an electrode based on p.1,1,3,3-tetramethylbutylcalix[6]arene-hexaacetic acid hexaethyl ester showed the highest response to methylammonium among various organic ammonium ions and inorganic cations. We further developed serotonin and mexiletine electrodes using the electrostatic interaction between the NH3+ group of these amines and the negatively polarized oxygen atoms in the phosphoryl (P=O) groups of phosphorus compounds. Among a series of the phosphorus compounds containing P=0 groups, tris(2-ethylhexyl)phosphine oxide and S, S, S-tris(2-ethylhexyl) phospho otrithioate proved to be effective for constructing serotonin and mexiletine electrodes, respectively.As for the application of ion-selective electrodes, we used K+ and tetraphenylphosphonium electrodes simultaneously in order to evaluate the ability of antimicrobial peptides to form channels (or more generally to increase permeability) and to abolish membrane potential in bacterial cytoplasmic membranes in situ. Furthermore, the changes induced by biologically active substances in the permeability to K+ and calcein of liposomes were measured simultaneously in order to rapidly screen the sizes of pores formed in a membrane, using different sized markers. We also applied K+ electrode to analyze gastric mucosal cell damage mediated by non-steroidal anti-inflammatory drugs.