Discrimination among Octylamine Isomers by Polymeric Membrane Electrodes Based on Lipophilic Calix[6]arene Tetraester Derivatives

Abstract

Liquid membrane type ion-selective electrodes (ISEs) provide one of the most powerful sensing methods because they afford the ability to select various sensory elements according to the shape and size of the target ion. Liquid membrane type electrodes for inorganic cations, such as sodium, potassium and lithium based on the host-guest chemistry, have been developed using crown ethers and related macrocyclic hosts as well as acyclic ligands.1-11 Many of these inorganic cation-selective electrodes exhibit excellent selectivity for analyte cations and are now commercially available. 12-16For organic cation-ISEs based on derivatives of crown ether or natural ionophore, as reported thus far, there are not many of these ISEs that respond strongly enough to discriminate among organic guests, and the selectivities of these electrodes are mostly controlled by the lipophilicity of the guest. 7-18Recently, calixarenes have received considerable attention as an interesting class of ionic and molecular binding hosts, 19,20 and studies show that various functionalized calixarenes are selective host molecules for cations as well as anions. [21][22][23][24][25][26][27][28][29][30][31][32] The well-defined structure of the calixarene cavity could also be investigated for inclusion of organic guests. Actually, calix [4] 33-39 Calix[6]arene has a sufficiently large cavity so that it can accommodate organic guests, whereas the calix[4]arene cavity is too small for ordinary organic guests. In addition, the tetraester of calix [6]arene affords an excellent binding site for protonated primary amines, because the NH3 + moiety of these guests can bind strongly to the inward-directed ester carbonyl groups of the host by hydrogen bonds. 29 In the present study, synthesized lipophilic tetraesters of calix [6]arene and calix-[6]diquinone reported as cesium-selective ionophores 30 were exploited as the sensory element of a PVC matrix liquid membrane electrode for organic amines (protonated form). The potentiometric response properties were examined for octylamine, 1-methylheptylamine, 2-ethylhexylamine and tertoctylamine as octylamine isomers and phenethylamine. Experimental SectionReagents. Lipophilic tetraesters of calix [6]arene and calix[6]diquinone tested as octylamine ionophores are shown in Figure 1. They were prepared according to the procedures reported by our group.32 High molecular weight PVC, dioctyl sebacate (DOS), potassium tetrakis(p-chlorophenyl)borate (KTpClPB) and tetrahydrofuran (THF), which were obtained from Fluka (Buchs, Switzerland), were used to prepare the PVC membranes. As guests for the potentiometric measurements, the following amines were purchased: octylamine, 1-methylheptylamine, 2-ethylhexylamine, tert-octylamine and phenethylamine from Aldrich Chemical Co. (Milwaukee, WI USA). All guests were prepared with hydrochloric acid salts. The structures of all guests are shown in Figure 1. Doubly distilled water in a quartz apparatus was used to prepare all aqueous electrolyte solutions.Fabrication of polymeric ion-s...

Solid-contact ion-selective electrodes for potentiometric determination of phenylethylamine in vitro

“…However, only a small number of PEA ISEs is reported. The liquid selective membranes consist of acridine-18-crown-6, organoboron components and calix [6]arene tetraester derivatives as ionophores both show potentiometric sensitivity toward PEA [27][28][29]. In these conventional ISEs, the working electrodes contain polymeric selective membranes and internal filling electrolytes with high concentrations of chloride ion, to obtain a stable potential at the inner surface.…”