Metal Sensing and Radical Quenching Properties of Thiophene-basedHydrazone

Metal ion sensing properties of thiophene based hydrazone (TH) have been studied using UV-Vis and DFT studies. In comparison to heavy transition metal ions, TH especially binds to Cu<sup>2+</sup> and Fe<sup>3+</sup> ions. The lower limit of detection (LOD) of the compound is 6 μM and 9 μM for Cu<sup>2+</sup> and Fe<sup>3+</sup> ions respectively. The binding constant for the compound: Cu<sup>2+</sup> and compound: Fe<sup>3+</sup> complexes are obtained as 3 x 10<sup>4</sup> M<sup>-1</sup> and 4.5 x 10<sup>3</sup> M<sup>-1</sup> respectively using the Benesi-Hildebrand plot. The stoichiometry ratio for compound: Cu<sup>2+</sup> complex 2:1 is obtained using Job's plot. The complex is more stable than the free compound and is validated through computation of HOMO-LUMO orbital energy and band gap of compound and complex using density functional theory. TH exhibits antioxidant properties against the DPPH radical with IC<sub>50</sub>: 23 μM. The possible mechanism of quenching of radical is suggested through single electron transfer followed by a proton transfer mechanism. From the above studies, it can be concluded that the hydrazone TH detects both Cu<sup>2+</sup> and Fe<sup>3+</sup> ions up to micromolar concentration and quenches the DPPH radical with IC<sub>50</sub> comparable to vitamin E.