Aminothiazole-Linked Metal Chelates: Synthesis, Density Functional Theory, and Antimicrobial Studies with Antioxidant Correlations

Abstract

During the current study, the new aminothiazole Schiff base ligands (<b>S¹</b> ) and (<b>S²</b> ) were designed by reacting 1,3-thiazol-2-amine and 6-ethoxy-1,3-benzothiazole-2-amine separately with 3-methoxy-2-hydroxybenzaldehyde in good yields (68-73%). The ligands were characterized through various analytical, physical, and spectroscopic (FT-IR, UV-Vis, ¹H and ¹³C NMR, and MS) methods. The ligands were exploited <i>in lieu</i> of chelation with bivalent metal (cobalt, nickel, copper, and zinc) chlorides in a 1:2 (M:L) ratio. The spectral (UV-Vis, FT-IR, and MS), as well as magnetic, results suggested their octahedral geometry. The theoretically optimized geometrical structures were examined using the M06/6-311G+(d,p) function of density function theory. Their bioactive nature was designated by global reactivity parameters containing a high hardness (η) value of 1.34 eV and a lower softness (σ) value of 0.37 eV. Different microbial species were verified for their potency (<i>in vitro</i>), revealing a strong action. The Gram-positive <i>Micrococcus luteus</i> and Gram-negative <i>Escherichia coli</i> gave the highest activities of 20 and 21 mm for compounds (<b>8</b>) and (<b>7</b>), respectively. The antifungal activity against the <i>Aspergillus niger</i> and <i>Aspergillus terreus</i> species gave the highest activities of 20 and 18 mm for compounds (<b>7</b>) and (<b>6</b>), respectively. The antioxidant activity, evaluated as DPPH and ferric reducing power, gave the highest inhibition (%) as 72.0 ± 0.11% (IC₅₀ = 144 ± 0.11 μL) and 66.3% (IC₅₀ = 132 ± 0.11 μL) for compounds (<b>3</b>) and (<b>8</b>), respectively. All metal complexes were found to be more biocompatible than free ligands due to their chelation phenomenon. The energies of LUMOs had a link with their activities.