Development of Conductometric Sensor Based on 25,27-Di-(5-thio-octyloxy)calix[4]arene-crown-6 for Determination of Ammonium

The conductometric sensor based on 25,27-di-(5-thio-octyloxy)calix[4]arene-crown-6 was developed for the quantitative analysis of ammonium. The calixarene was immobilized on the surface of the planar interdigitated electrodes by attachment of its dialkyl sulfide groups to the surface of the gold electrodes. The intrinsic ability of the calixarene to capture ammonium was studied in the conductometric measuring mode and by the electrochemical impedance spectroscopy. The developed sensor showed high selectivity to ammonium in the presence of mono-, di-, and trivalent cations. Selective and highly sensitive detection of ammonium resulted from the complexation between the ammonium ions and a crown-ether fragment of the upper rim of the 25,27-di-(5-thio-octyloxy)calix[4]arene-crown-6 macrocycle. The developed sensor had high signal repeatability. Its sensitivity was found to be satisfactory for the forthcoming sensor application in the water-sample analysis; the linear range was 0.01-1.5 mM and limit of detection 10 μM.

Synthesis and Structure of Upper-Rim 1,3-Alternate Tetraoxacalix[2]arene[2]triazine Azacrowns and Change of Cavity in Response to Fluoride Anion

The upper-rim 1,3-alternate tetraoxacalix[2]arene[2]triazine azacrowns were constructed effectively by macrocyclic condensation reaction of diamines with dichlorinated tetraoxacalix[2]arene[2]triazine intermediates that were synthesized from the stepwise fragment coupling reactions of 3,5-dihydroxybenzoic acid esters with cyanuric chlorides. Because of the formation of conjugation of amino groups with triazine rings, tetraoxacalix[2]arene[2]triazine azacrowns existed in a mixture of syn- and anti-isomeric forms. Both fluorescence titration and 1H NMR spectroscopic study showed that tetraoxacalix[2]arene[2]triazine azacrowns interacted with fluoride anion, leading to cavity changes of the host molecules.

Molecular recognition in methanol: the first example of hydrogen-bond-mediated self-association of a calix[4]arene in polar, protic solvent

Tetraalaninecalixarene was prepared by coupling of tetraaminocalix[4]arene with alanine. It dimerizes in methanol, providing the first example of a substituted calixarene that undergoes self-association through hydrogen bonding in polar, protic solvent. The association constant in 24:1 MeOH:H2O was determined to be 29 000 M-1. Addition of arginine or lysine results in disruption of the dimer and formation of a 1:1 complex between the amino acid and the tetraalaninecalixarene. The preparation of a peptidocalixarene that associates in polar solvent opens new doors for the use of calixarenes for molecular recognition in biologically relevant environments.