Synthesis, characterization, fluorescence and catalytic activity of some new complexes of unsymmetrical Schiff base of 2-pyridinecarboxaldehyde with 2,6-diaminopyridine

Spectroscopic investigation, thermal behavior, catalytic reduction, biological and computational studies of novel four transition metal complexes based on 5-methylthiophene Schiff base type

Four new complexes prepared from 5-Methyl-2-carboxaldehyde-thiophene and 2,6-pyridinediamine with cobalt, nickel, copper and cadmium ions have been synthesized because of the significance of these complexes in pharmacological research and catalytic reduction. The prepared compounds were characterized using elemental analysis, mass, UV-visible, NMR and FTIR spectroscopy, as well as molar conductance, magnetic susceptibility measurements, fluorescence properties and TGA analysis. The stoichiometry mode was confirmed as 1:1 (metal: ligand) for Co, Ni and Cu complexes and 1:2 (metal: ligand) for Cd complex according to the results of the elemental and spectral studies. Furthermore, the thermal stability and luminescence properties of complexes have been studied. Thermal studies confirmed the presence of water molecules. The thermodynamic properties of the complexes were measured via the Coats-Redfern procedure. The geometric structures of the complexes were found to be octahedral around the metal ions. The optical energy gaps (Eopt) vary between 2.92 and 3.71 eV indicating that these compounds can be used as selective absorbing solar energy in photovoltaic applications. In the presence of NaBH₄, the greatest reduction efficiency for the conversion of 2-NP to 2-AP was discovered to be 73-91% within 15-25 min. In vitro, high antifungal and antibacterial activity was shown by complexes than the ligand alone. The Cd(II) complex was shown to have greater activity than all of the examined microorganisms when compared to the reference drug in addition it had 4.94 μg/ml minimal inhibitory concentration against "S. aureus", "B. subtilis", and "E. coli". The bond angles, bond lengths, and quantum chemical factors of the ligand and complexes were shown in the molecular modeling using the DFT approach. The studied compounds' binding modes were confirmed using the Gaussian 09 program.

Synthesis, anti-bacterial evaluation, DFT study and molecular docking as a potential 3-chymotrypsin-like protease (3CLpro) of SARS-CoV-2 inhibitors of a novel Schiff bases

New Schiff bases {N'-(phenyl(pyridin-2-yl)methylene) isonicotinohydrazide (L¹H), N¹ -(naphthalen-1-yl)-N² -(phenyl(pyridin-2-yl) methylidene) ethane-1,2-diamine (L²H), N-(6-chlorobenzo[d]thiazol-2-yl)-1-phenyl-1-(pyridin-2-yl) methanimine (L³H)}were synthesized by reaction of 2-benzoylpyridine with different amines (2-amino-6-chlorobenzothiazole, isonicotinohydrazide and N ¹-(naphthalen-1-yl)ethane-1,2-diamine) and characterized by ¹H-NMR, ¹³C-NMR, IR mass spectroscopy and elemental analysis. The compounds were assayed by the disc diffusion method for anti-bacterial against five pathogenic bacteria species (Staphylococcus aureus, Micrococcus luteus, Staphylococcus pyogenes, Bacillus subtilis, and E. coli). All prepared Schiff bases showed good activity compared to positive control (streptomycin), Moreover the L³H showed the highest activity against S. aureus, and M. luteus than the other compounds and streptomycin. In additional molecular docking studies with 3-chymotrypsin-like protease (3CLpro), the essential enzyme for SARS-CoV-2 proliferation. The rest of compounds have shown promising results as 3CLpro inhibitors interacting with the active sites of the enzymes. Finally, DFT 's estimated electrostatic molecular potential results were used to illustrate the molecular docking findings. The DFT calculations showed that L³H has the highest dipole moment and electrophilicity index. Interestingly, L²H of the largest energy gap ∆E = 2.49 eV, there are several hydrophilic interactions that could facilitate the binding with the receptors. All of these parameters could be shared to significantly affect the protein sites of binding affinity with different extent.

A selective naked-eye chemosensor derived from 2-methoxybenzylamine and 2,3-dihydroxybenzaldehyde - synthesis, spectral characterization and electrochemistry of its bis-bidentates Schiff bases metal complexes

A new colorimetric receptor HL, acting as a bidentate Schiff base ligand, has been synthesized by condensation of 2-methoxybenzylamine on 2,3-dihydroxybenzaldehyde in a methanolic solution. Interestingly, this chelating agent can selectively detect Cu²⁺, Co²⁺, Fe²⁺ and Fe³⁺ ions with a simple and an easy-to-make, well defined naked-eye visible color changes in two different solvents like acetonitrile and methanol. This bidentate ligand coordinates three metal ions of Co(II), Cu(II) and Fe(II) via nitrogen and oxygen atoms. The molecular structures of the synthesized compounds were elucidated by various physicochemical properties such as the elemental analysis, FT-IR, HNMR, UV-Vis and the Mass spectrometry. The resulting general formulae [M(L)₂·H₂O] (M(II)=Cu, Fe, Co) are proposed as mononuclear complexes. The solvatochromism properties of these compounds were studied with their absorption spectra using different solvents as methanol (MeOH), acetonitrile (AN), tetrahydrofuran (THF), dimethylformamid (DMF), dimethylsulfoxid (DMSO) and dichloromethane (DC). The Electrochemical behavior of copper complex was explored in DMF solutions by cyclic voltammetry (CV) with two working electrodes: glassy carbon (GC) and platinum electrode (Pt). This study reveals that copper complex shows successively two redox systems as Cu^III/II and Cu^II/I. The Fe^III/II and Co^II/I redox systems have also been studied in DMF and DMSO media.