Molecular Design of Calixarene, Part 4, Synthesis of Novel Double-Armedp-(tert-Butyl)calix[4]arene-Derived Amides and Their Lead(II)(Pb2+)-Selective-Electrode Properties

Abstract

A series of novel double-armed p-(tert-butyl)calix[4]arenes, carrying benzoylamido, 4-nitrobenzoylamido, isonicotinamido, α-naphthamido, acetamido, propionamido, or butyramido groups (see 2 – 8, resp.) were synthesized in 80 – 86% yield by the reaction of the lower-rim 1,3-bis(aminoethoxy)-substituted calix[4]arenediol 1 with the corresponding acylating agents. Their structures were established by elemental analysis, mass, IR, UV, and 1H-NMR spectroscopy. Ion-selective electrodes (ISEs) for Pb2+, carrying 2 – 8 in a PVC membrane as neutral ionophore, were prepared, and their selectivity coefficients for Pb2+ (K) were determined against other heavy-metal ions, alkali and alkaline earth metal ions, and ammonium ions by means of the separate-solution method. The results obtained indicated that the electrodes based on the calix[4]arene-derived amides 2 – 8 as the neutral ionophores were all Pb2+ selective and exhibited almost theoretical Nernstian slopes, except for 3 and 4. Typically, the Pb2+-selective electrode based on 6 – 8 exhibited almost Nernstian slopes for Pb2+ over a relatively wide concentration range and had a fast response time as well as a long lifetime, although the silver ion interfered strongly. These ISEs based on 6 – 8 showed a relatively good Pb2+ selectivity against most of the interfering cations examined, except for Ag+. The effect of the side-arm functions of calix[4]arene derivatives 2 – 8 on the Nernstian slopes and on the selectivity coefficients for Pb2+ obtained with the Pb2+ ISEs based on 2 – 8 is discussed.