Hydrogen-bond forming ionophore for highly efficient transport of phosphate anions across the nitrobenzene–water interface

Abstract

Thiourea-based hydrogen-bond forming ionophore 2, alpha,alpha'-bis(N'-p-nitrophenylthioureylene)-m-xylene, is synthesized and investigated by using ion transfer polarography for the facilitated transfers of H2PO4-, HPO42- and Cl- across the nitrobenzene-water interface. Bis-thiourea 2 has a significant ability to assist H2PO4- transfer across the interface whereas its counterpart, N-(p-nitrophenyl)-N'-propylthiourea (ionophore 3), cannot facilitate the transfer of this hydrophilic anion. The H2PO4- transfer assisted by 2 is based on the formation of a 2:1 complex between H2PO4- and ionophore, and the transfer reaction is more stable by over -12 kJ mol(-1) than the case of 3. The stabilization of the H2PO4- transfer for 2 is even stronger by -11 kJ mol(-1) than that for bis-thiourea 1, 2,7-di-t-butyl-4,5-bis(N'-butylthioureylene)-9,9-dimethylxanthene, which forms a 1:1 complex through the formation of four hydrogen bonds. Bis-thiourea 2 is also able to facilitate transfers of HPO42- and Cl- by the formation of 1:1 complex. As compared to bis-thiourea 1, HPO42- transfer by 2 is significantly stabilized by -27 to -31 kJ mol(-1) while the stabilization of the Cl- transfer is relatively moderate (-6.1 kJ mol(-1)). These binding properties of bis-thiourea 2 are discussed for the design of phosphate-selective ionophores for use in two-phase distribution systems such as ion-selective electrodes.

Evaluation of healthy and sensory indexes of sweetened beverages using an electronic tongue

“…This interaction would be similar to that described, based on studies concerning the structure-activity relationships, between hydroxyl groups in sweet-tasting sugars and the human sweet taste receptor [32]. In fact, literature [29,32,48,49] reports that the electric response of potentiometric E-tongue to sugars may be due to the interaction on the surface of the lipid/polymer membrane (at the oil/water interface), either derived from the establishment of hydrogen bonds or due to the presence of some mediating electrolyte substances, between carboxyl or phosphate groups in the lipid/polymer membrane and the two vicinal hydroxyl groups of the sugar molecules. The response of the potentiometric E-tongue towards the organic acids present in the fruit beverages, may be explained since these molecules, which are electrolytes, electrically interact with the lipid/polymer membrane and after being adsorbed induce a change in the membrane potential [30,31].…”

Sweetness Sensor with Lipid/Polymer Membranes: Response to Various Sugars

“…Moreover, it seems that this interaction itself must occur on the surface of the lipid/polymer membrane of the sweetness sensor, that is, oil/water interface, like in the other examples reported. (13,14) However, even if such an interaction itself may be possible there, the reason why an electric potential change is observed in the sweetness sensor from sugars, which are nonelectrolytes, is still unknown. On the other hand, if the interaction is indirect, then, there may be some mediating substances between the carboxyl group and the two vicinal hydroxyl groups.…”

Electroanalytical Opportunities Derived from Ion Transfer at Interfaces between Immiscible Electrolyte Solutions

“…The assisted transfer of phosphate at water/DCE interfaces employing a bis-urea-calix [4]arene [80] as receptor was reported, together with a similar study at water/NB interfaces with a bis-thiourea ligand. [81] Shao et al [82] reported the facilitated ion transfer of four anions (NO2 -, Cl -, Br -and COO -) facilitated by calix-pyrrole ligands at a micro-interface, while Dryfe and colleagues [83] reported the transfers of a series of anions facilitated by a cholapod ionophore, and determined their complexation constants.…”