Synthesis, structural characterization of phenoxo-bridged zinc(II) complexes and their binding interaction with the spike protein of SARS-CoV-2

The research article reports the synthesis and structural study of the optimized geometry of selenium (Se) bearing 24- and 28- membered macrocyclic Schiff bases, L a H 2, L b H 2 and their reactions with zinc metal ion. The reactions of the macrocyclic Schiff bases with ZnCl₂ in 1:2 molar ratios result in the formation of bimetallic Zn(II) complexes having molecular composition [Se{(CH₂)₂N = CPh(4-CH₃-C₆H₂O) PhC = O}₂ · Zn₂Cl₂], (1) and [Se{(CH₂)₃N = CPh(4-CH₃-C₆H₂O)PhC = O}₂ · Zn₂Cl₂], (2). Moreover, as confirmed by various physico-chemical techniques such as elemental analysis, UV–Vis, FTIR,¹H NMR, and mass spectrometry, the proligands underwent partial hydrolytic cleavage at one of the C = N positions and behave like hexadentate (N₂O₄) ligands binding to two Zn(II) ions via bridging through the O_phenolic atoms, which results in a square pyramidal geometry around Zn(II) with the chlorine atom occupying axial positions. Further, following density functional study, the stable optimized configuration of the Schiff bases L a H 2 and L b H 2 is found to adopt bowl shape geometry. Conversely, in molecular docking studies, the synthesized complex 1 exhibits a significantly stronger binding affinity (−8.7 kcal/mol) to the spike protein of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) as compared to the common coronavirus disease 2019 (COVID-19) treatment drugs such as chloroquine, hydroxychloroquine, and remdesivir with activity percentage showing more than 20% overall effectiveness than remdesivir and thus indicating its potential for COVID-19 therapeutics.