Chloride‐Selective Electrodes Based on “Two‐Wall” Aryl‐Extended Calix[4]Pyrroles: Combining Hydrogen Bonds and Anion–π Interactions to Achieve Optimum Performance

Abstract

The performance of chloride-selective electrodes based on "two-wall" aryl-extended calix[4]pyrroles and multiwall carbon nanotubes is presented. The calix[4]pyrrole receptors bear two phenyl groups at opposite meso-positions. When the meso-phenyl groups are decorated with strong electron-withdrawing substituents, attractive anion-π interactions may exist between the receptor's aromatic walls and the sandwiched anion. These anion-π interactions are shown to significantly affect the selectivity of the electrodes. Calix[4]pyrrole, bearing a p-nitro withdrawing group on each of the meso-phenyl rings, afforded sensors that display anti-Hofmeister behavior against the lipophilic salicylate and nitrate anions. Based on the experimental data, a series of principles that help in predicting the suitability of synthetic receptors for use as anion-specific ionophores is discussed. Finally, the sensors deliver excellent results in the direct detection of chloride in bodily fluids.

New dimensions in calix[4]pyrrole: the land of opportunity in supramolecular chemistry

“…5), thereby highlighting the potential roles being played by different aryl-p substituents in anion-p contact. 33,65,66 Researchers worldwide have also carried out the synthesis of various other mesosubstituted two and four-walled C4Ps (Fig. 6).…”

Construction of Supramolecular Assemblies Based on Anion–π Interactions

“…A significant investigation that highlights the importance of the anion-π interactions in emerging fields of research has been reported by Sabek et al [124] They have demonstrated the performance of chloride-selective electrodes based on "two-wall" aryl-extended calix [4]pyrroles and multiwall carbon nanotubes. When the meso-aryl substituents of the calix [4]pyrrole core are electron deficient, attractive anion-π interactions exist between the aromatic walls of the receptor [I 3 ] -HIRKUQ FIgURE 11.17 The X-ray crystal structure of HIRKUQ [116].…”

Fluorinated tripodal receptors for potentiometric chloride detection in biological fluids

“…While most chloride-selective ionophores reported in the past are organometallic compounds, some active membrane components reported recently are based on chloride complexation by hydrogen bonds. (Sabek et al, 2015;Xiao et al, 1997;Zahran et al, 2010) Commonly used chloride-selective receptors with a metal center such as mercury, manganese or indium (Kondo et al, 1989;Park et al, 1991;Radu and Bakker, 2005;Rothmaier et al, 1996) often exhibit stability and/or toxicity issues. (Sabek et al, 2015) It is noted that most proposed receptors, both neutral and charged carriers, do not provide better selectivity and stability of chloride detection for clinical applications than traditional ion-exchanger based membrane (TDMACl).…”

“…(Sabek et al, 2015;Xiao et al, 1997;Zahran et al, 2010) Commonly used chloride-selective receptors with a metal center such as mercury, manganese or indium (Kondo et al, 1989;Park et al, 1991;Radu and Bakker, 2005;Rothmaier et al, 1996) often exhibit stability and/or toxicity issues. (Sabek et al, 2015) It is noted that most proposed receptors, both neutral and charged carriers, do not provide better selectivity and stability of chloride detection for clinical applications than traditional ion-exchanger based membrane (TDMACl). (Bratov et al, 2004) Consequently, the selectivity pattern of ISEs based on lipophilic quaternary ammonium salts (such as TDMACl) is fixed and follows the Hofmeister series since the selectivity of ion exchanger is mainly defined by the lipophilicity the ion.…”