Synthesis, Characterization, and Anti-<i>TB</i> Application of Redox-Active Ethyl Carbazate-Derivatized Phenanthroline and Its Silver Complexes

Exploring the design and synthesis of new antibiotic compounds is important to treat multidrug-resistant bacterial infections for the already exposed drug molecules. In this work, a phenanthroline derivative, namely, 6-[2-(ethoxycarbonyl)-diazen-1-yl]-1,10-phenanthroline-5-one (ECDPO), and its mono- and bis-ligand silver complexes [Ag-(ECDPO)-(NO₃)] and [Ag-(ECDPO)₂]-(NO₃) were synthesized. Single-crystal X-ray diffraction (XRD) structure of methanol-solvated ECDPO was studied, which crystallized in a monoclinic system, <i>P</i>2₁/<i>n</i> space group. ECDPO is a planar molecule, and supramolecular arrays are stabilized by various hydrogen bonding, namely, O-H···N, N-H···O, and C-H···O, and π-π interactions. The spectroscopic features of ECDPO and its silver complexes were thoroughly studied by high-resolution mass spectrometry (HRMS), IR, ¹H NMR, ¹³C NMR, UV-visible spectroscopy, and X-ray photoelectron spectroscopy (XPS). Electrochemical redox features were studied by cyclic voltammetry. The ECDPO molecule and its silver complexes were studied for antibacterial activity against <i>Escherichia coli</i> bacteria and <i>Mycobacterium tuberculosis</i> (<i>Mtb</i>). ECDPO shows a minimum inhibitory concentration (MIC) of 1.56 μg/mL against <i>Mtb</i>, which is comparable to that of one of the clinically used drug candidates, namely, ethambutol. Silver complexes [Ag-(ECDPO)-(NO₃)] and [Ag-(ECDPO)₂]-(NO₃) showed enhanced anti<i>-TB</i> activities and MICs of 0.78 and 0.39 μg/mL, respectively.