Thiosemicarbazone- and Thiourea-Functionalized Calix[4]arenes in <i>cone</i> and 1,3-<i>alternate</i> Conformations: Receptors for the Recognition of Ions
2025
Andrés Ochoa | Belén Hernández-Arancibia | José Herrera-Muñoz | Horacio Gómez-Machuca | Claudio Saitz
In this research we have synthesized and evaluated five calix[4]arene-based receptors functionalized with thiosemicarbazone or thiourea groups, incorporating pyridinyl naphthalene or triazolopyridine chromophores in 1,3-<i>alternate</i>, pinched <i>cone</i> and <i>cone</i> conformations. The ion recognition capabilities of these receptors were investigated using UV-visible and fluorescence spectroscopy. Receptor (<b>I</b>), which adopts a pinched <i>cone</i> conformation with thiosemicarbazone groups, demonstrated bifunctional sensing abilities by detecting both cations and anions. Receptors (<b>II</b>) and (<b>III</b>) showed remarkable selectivity and sensitivity for Cu<sup>2+</sup> ions. Receptors (<b>IV</b>) and (<b>V</b>), in <i>cone</i> and 1,3-<i>alternate</i> conformations, respectively, where functionalized with a triazolo[1,5-a]pyridine fluorophore and exhibited highly sensitive ON-OFF fluorescence sensing for Co<sup>2+</sup>, Cu<sup>2+</sup> and Ni<sup>2+</sup> ions, with significant fluorescence quenching upon binding and a low detection limit of 2.94 µg/L for the Co<sup>2+</sup> ion in receptor (<b>IV</b>). Ion receptor (<b>I</b>) demonstrates a strong performance in broad-spectrum ion detection, whereas the structural conformations of receptors (IV) and (V) play a pivotal role in their remarkable selectivity and sensitivity for specific transition metals in fluorescence-based sensing.
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