Development and application of high-performance electrochemical sensors for detecting biologically active substances

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The development and application of electrochemical sensors including ion selective electrode continue to be an area of focus. In this study, we developed new organic ammonium ion selective electrodes using homooxacalix[3]arene and calixarene derivatives. These derivatives with C_3 or C_6 symmetry are known to be effective in the recognition of primary organic ammonium ions. Since primary ammonium ions act as C_3-symmetrical proton donors, receptors bearing a C_3 symmetrically arranged proton acceptor site can interact with primary ammonium ions. Moreover, the hydrophobic cavities generated by the aromatic walls of phenol residues of these derivatives are potentially useful for the inclusion of non polar moieties of organic ammonium ions. In the process of screening homooxacalix[3]arene and calix[6]arene derivatives for responses to various organic ammonium ions including biogenic amines, we found that tris(methoxyphenylpropyloxy)hexahomooxacalix[3]arene-triethyl ether, responds strongly to serotonin, while p-tert-butylcalix[6]arene-hexaacetic acid hexaethyl ester responds to ethylammonium. This suggested that the cavity of homooxacalix[3]arene was spread out enough to interact with large molecules such as serotonin, while the cavity of calix[6]arene was so small, leading to effective interaction with ethylammonium. We also found that calix[8]arene, having larger cavity than calix[6]arene, responded to biologically active amines having a complicated structure, such as norephedrine. Calix[8]arene derivatives made effective recognition of bulky and complicated organic ammonium ions, using a large cavity and choosing an appropriate position at the proton acceptor sites to interact with these primary amines.We also applied ion selective electrodes to analyze the interaction between polyamines and the outer membrane of Escherichla coli cells. This and other results obtained in this study can be seen through references described in the back of this report.