This research study reports the synthesis, structural characterization and phenoxazinone synthase-like activity of two structurally similar copper(II) complexes developed with a benzimidazole functionalized Schiff base (L). The ligand, L, was designed and synthesized in high yield by the reaction of p-methoxy benzaldehyde with o-phenylenediamine. The reaction of L with CuCl 2 and Cu(NO 3 ) 2 leads to the formation of two isostructural complexes, [Cu(L) 2 Cl 2 ] 2 (1) and [Cu(L) 2 (NO 3 ) 2 ] 2 (2). Single crystal X-ray structural study reveals that both the Cu(II) centre in 1 and 2 adopts a square planar geometry. An attempt has also been made to understand the role of coordinated coligands on the catalytic oxidation of 2-aminophenol (2-AP) to 2-amino-3Hphenoxazine-3-one (2-APX) in methanol. The presence of coordinated nitrate to Cu(II) ions imparts a more labile character to complex 2, and the catalytic efficiency (k cat /K M ) for complex 2 (1.50 × 10 7 ) was determined almost double compared with that of complex 1 (8.78 × 10 6 ). Electro-chemical and electrospray ionization mass spectrometry studies of 1 and 2 with 2-AP suggests that the square planar geometries of the Cu(II) centres remain the driving force to develop enzyme-substrate adducts and excellent catalytic performance of the complexes. Electrochemical and EPR spectral analysis of the reaction mixture confirm the presence of active 2-AP − /2-AP •− redox species in the course of catalytic oxidation and suggest the radical driven oxidative coupling of 2-AP in an aerobic environment. Temperature-dependent kinetic measurements were carried out to evaluate the activation parameters (E a , ΔH ‡ , ΔS ‡ ), which favours the higher rate of catalytic oxidation of 2-AP for complex 2 than complex 1.

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Phenazine scaffolds are the versatile secondary metabolites of bacterial origin. It functions in the biological control of plant pathogens and contributes to the producing strains ecological fitness and pathogenicity. In the light of the excellent therapeutic properties of phenazine, we have synthesized a hydrated 2,3-diaminophenazinium chloride (DAPH+Cl−·3H2O) through direct catalytic oxidation of o-phenylenediamine with an iron(III) complex, [Fe(1,10-phenanthroline)2Cl2]NO3 in ethanol under aerobic condition. The crystal structure, molecular complexity and supramolecular aspects of DAPH+Cl− were confirmed and elucidated with different spectroscopic methods and single crystal X-ray structural analysis. Crystal engineering study on DAPH+Cl− exhibits a fascinating formation of (H2O)2…Cl−…(H2O) cluster and energy framework analysis of defines the role of chloride ions in the stabilization of DAPH+Cl−. The bactericidal efficiency of the compound has been testified against few clinical bacteria like Streptococcus pneumoniae, Escherichia coli, K. pneumoniae using the disc diffusion method and the results of high inhibition zone suggest its excellent antibacterial properties. The phenazinium chloride exhibits a significant percentage of cell viability and a considerable inhibition property against SARS-CoV-2 at non-cytotoxic concentration compared to remdesivir. Molecular docking studies estimate a good binding propensity of DAPH+Cl− with non-structural proteins (nsp2 and nsp7-nsp-8) and the main protease (Mpro) of SARS-CoV-2. The molecular dynamics simulation studies attribute the conformationally stable structures of the DAPH+Cl− bound Mpro and nsp2, nsp7-nsp8 complexes as evident from the considerable binding energy values, − 19.2 ± 0.3, − 25.7 ± 0.1, and − 24.5 ± 0.7 kcal/mol, respectively.

A metal‐free methodology for the synthesis of 1,2‐disubstituted and 2‐substituted benzimidazoles with high to excellent yields has been developed. The course of synthesis involves easy work‐up, straightforward purification, inexpensive reaction setup, and wide substrate scope under extremely mild and operationally simple conditions which makes the synthetic strategy more lucrative, practical and reliable. The serious challenge to carry out these reactions in a pure aqueous medium has been achieved at 75 °C in presence of air bubbles. The applicability of this operationally simple and metal‐free synthetic approach for the gram‐scale synthesis of benzimidazole derivatives with good yield (∼74%) further strengthens its potentiality for the synthesis at an industrial scale.

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