Biological and equilibrium studies of Co(II), Cu(II), Zn(II), and Cd(II) complexes of 1‐formyl‐3‐semicarbazide: Docking studies

Abstract

1‐Formyl‐3‐semicarbazide (FSC, HL) and its metal complexes with Co(II), Cu(II), Zn(II), and Cd(II) ions have been synthesized and characterized by elemental analysis, liquid chromatography‐mass spectrometry (LC–MS), infrared (IR), electronic, nuclear magnetic resonance (NMR) and electron spin resonance (ESR) spectroscopy, thermogravimetric analysis (TGA), magnetic susceptibility, and conductivity measurements. The chelates are non‐electrolytic in nature with distorted octahedral geometry. The kinetic and thermodynamic properties were calculated using the Coats–Redfern relation results in positive enthalpy change values and negative entropy change values. The equilibrium studies of FSC with Co(II), Zn(II), and Cd(II) ion have been carried out by potentiometric pH titrations in 70% v/v DMF‐water medium at 303 K and 0.1 M (KNO3) ionic strength. The study revealed that FSC is monobasic acid with pKa value of 8.84. The stability constants suggested the formation of 1:1 Co(II)‐FSC complex, and Zn(II)‐FSC and Cd(II)‐FSC systems revealed the formation of both 1:1 and 1:2 complexes in the solution. DNA binding studies for the metal chelates have been carried out using electronic absorption spectra, fluorescence emission spectra, and viscosity measurements revealing groove binding for Co(II), and Zn(II) complexes, and intercalation mode of binding for Cu(II)‐FSC complex with CT‐DNA. The Kb values from absorption studies are Co(II)‐FSC = 0.9990 × 102, Cu(II)‐FSC = 2.433 × 104, and Zn(II)‐FSC = 8.277 × 102 M−1, and the KSV values from the competitive fluorescence emission studies are Co(II)‐FSC = 0.19212 and Cu(II)‐FSC = 0.11482 M−1. Molecular docking carried out for both ligand and its Co(II) and Zn(II) complexes also revealed groove mode of binding, and Cu(II) complex showed intercalative mode of binding. The inhibition constants for HL, Co(II), Cu(II), and Zn(II) are 1460, 0.478, 0.122, and 0.194 μM, respectively. The antimicrobial activity has been studied using agar disk diffusion method against Escherichia coli and Bacillus subtilis. FSC has been found to be more active against gram +ve and gram –ve bacteria than its metal chelates.