Triazolophanes: A New Class of Halide-Selective Ionophores for Potentiometric Sensors

Abstract

Triazolophanes, cyclic compounds containing 1,2,3-triazole units, are a new class of host molecules that demonstrate strong interactions with halides. These molecules are designed with a preorganized cavity that interacts through hydrogen bonding with spherical anions, such as chloride and bromide. We have explored the use of one such triazolophane as a halide-selective ionophore in poly(vinyl chloride) (PVC) membrane electrodes. Different membrane compositions were evaluated to identify concentrations of the ionophore, plasticizer, and lipophilic additive that give rise to the best chloride and bromide selectivity. The lipophilicity of the plasticizer was found to have a great impact on the electrode response. Additionally, the concentration of the lipophilic additive was found to be critical for optimal response. The utility of a triazolophane-based electrode was demonstrated by quantification of bromide in horse serum samples.

Calix[4]pyrrole-based anion transporters with tuneable transport properties

“…10 1,2,3-Triazoles have recently been shown by Flood and others to be effective hydrogen bond donor groups 55 with the polarization of the heterocycle resulting in the CH group forming strong hydrogen bonding interactions with halides. 11 We found that the introduction of the triazole strap to compound 3 resulted in a new mode of transport across POPC membranes (chloride/nitrate antiport) that was not 60 observed with parent compound 1. We wished to examine more closely the role played by the strap in modulating the transport efficiency and mechanism of a calixpyrrole.…”

“…Bridging the parent calix [4]pyrrole with a mono-triazole strap dramatically hampers the formation of a satisfactory complex structure with H 2 PO 4 -as indicated by the loss of more than 6 kcal in binding enthalpy (entries 3 versus 11). Embedding another triazole unit into a strap of the same length, using host 4 as a 5 probe, then increases the enthalpic interaction by almost 12 kcal (entries 11,17). As such a massive boost cannot be sensibly accounted for by the formation of at best two novel and dedicated hydrogen bonds in acetonitrile solvent (ε = 36; the triazole module may donate and accept just one hydrogen 10 bond each) we are led to conclude that the covalent connectivity of the bis-triazolo host 4 creates the correct and necessary environment for H 2 PO 4 -anion to act as the missing piece in a mosaic of hydrogen bonding.…”

Electroanalytical Sensor Technology

“…For example, Alvarez-Romero et al [145] discuss the successful development of a graphite-based composite containing epoxy resin, doped with chloride ion doped polypyrrole, as a chloride ion selective electrode. Zahran et al [146] report a novel PVC-based sensor that exhibit selectivity toward halides (chloride and bromine specifically). Similarly Kang et al [147] describe the fabrication and characterisation of a PVC based Sc 3+ octaethylporphyrin composite fluoride selective electrode this is significant as fluoride selective sensors allow for rapid detection of toxic organic fluorophosphates, which can contaminate drinking water.…”

1,2,3-Triazoles and the Expanding Utility of Charge Neutral CH···Anion Interactions

“…With this greater understanding of how anions can affect key biological processes, research in the field of anion supramolecular chemistry -anion binding and remediation utilizing noncovalent interactions [10,11] -has seen exponential growth in the last 20 years. These activities have led to applications in ion selective electrodes [12][13][14], which can be used for measuring chloride and phosphate concentrations in the human body, as well as to the design of selective receptors for use in environmental anion remediation and liquid-liquid extractions [15,16]. At the foundation of these advances in anion receptor chemistry lies the application of new synthetic methodologies to allow for the creation of these novel receptors.…”

“…Incorporating anion receptors, or ionophores, into the electrode's membranes can alter the selectivities. Ion selective electrodes with triazolophane 14 as the ionophore were prepared and showed good responses to chloride and bromide [14]. A submicromolar detection limit and a dynamic range of five orders of magnitude toward both halides were found.…”