Synthesis of new coumarins complemented by quantum chemical studies

Transition metal complexes of a multidentate Schiff base ligand containing pyridine: synthesis, characterization, enzyme inhibitions, antioxidant properties, and molecular docking studies

A series of Fe(II), Ni(II), and Pd(II) complexes were prepared with a novel Schiff base ligand containing pyridine moiety. The prepared compounds were characterized using FT-IR, ¹H and ¹³ C NMR, UV-Vis, powder XRD, thermogravimetric analysis, mass spectra, magnetic susceptibility, and elemental analysis. The coordination geometry of Fe(II) and Ni(II) complexes were octahedral, where Fe(II) and Ni(II) metal ions were coordinated by an oxygen atom of the carbonyl group, a nitrogen atom of the azomethine moiety, and a phenolic oxygen atom. The Pd(II) complex had square planar geometry. All of the synthesized compounds were tested for their biochemical properties, including enzyme inhibition and antioxidant activities. According to the in vitro DPPH and FRAP antioxidant methods, the Schiff base ligand and its Fe(II)/Pd(II) complexes showed close antioxidant activities against the standards (BHA, BHT, ascorbic acid, and α-tocopherol). Enzyme inhibitions of the metal complexes were investigated against glutathione S-transferase (GST), acetylcholinesterase (AChE), and butyrylcholinesterase (BChE) enzymes. The best inhibition value (K_i) was observed for the Ni(II) complex against GST (2.63 ± 0.04 µM). Also, the Pd(II) complex showed the best inhibition value (10.17 ± 1.88 µM) against AChE. Molecular docking specified significant interactions at the active pockets of respective target enzymes. The Ni(II) complex exhibited good binding affinity against both BChE (- 9.0 kcal/mol and 9.36 ± 2.03 µM) and GST (- 7.0 kcal/mol and 2.63 ± 0.04 µM) enzymes.

The structural, spectral, frontier molecular orbital and thermodynamic analysis of 2-hydroxy 2-methyl propiophenone by MP2 and B3LYP methods

In the present work, we have studied the 2-hydroxy 2-methyl propiophenone (2H2MPP) theoretically as well as experimentally. The optimized molecular structure has been obtained by the density functional theory (DFT), second-order Moller–Plesset perturbation theory (MP2) and Hartree Fock (HF) in the gas phase as well as in different media like ethanol, DMSO and heptane. FT-IR and FT-Raman spectra were computed as well as recorded and fundamental vibrational wavenumbers were assigned. The electronic absorption spectra were calculated by employing the time-dependent density functional theory (TD-DFT) to get the information about excitation energies, oscillator strength and excited state geometries in gas phase and in different solvent media. Chemical activity and chemical stability obtained by HOMO-LUMO studies using a HF/6-31[Formula: see text]G and MP2/6-311[Formula: see text]G calculations. The chemical interpretation of hyperconjugation interactions obtained by the Natural Bond Orbital (NBO) analysis. Moreover, electrostatic potential (ESP) calculations performed to get the visual representation of relative polarity of molecule. Thermodynamic parameters like enthalpy, entropy, heat capacity, and Gibbs free energy computed with varying temperature from 10[Formula: see text]K to 500[Formula: see text]K. The aim of the current investigation is to find out the quantum chemical properties of the title compound which show an active role in the pharmaceutical and printing industries.

Experimental and theoretical studies of Schiff bases as corrosion inhibitors

Background

Relatively inexpensive, stable Schiff bases, namely 3-((4-hydroxybenzylidene)amino)-2-methylquinazolin-4(3H)-one (BZ3) and 3-((4-(dimethylamino)benzylidene)amino)-2-methylquinazolin-4(3H)-one (BZ4), were employed as highly efficient inhibitors of mild steel corrosion by corrosive acid.

Findings

The inhibition efficiencies were estimated based on weight loss method. Moreover, scanning electron microscopy was used to investigate the inhibition mechanism. The synthesized Schiff bases were characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy and micro-elemental analysis. The inhibition efficiency depends on three factors: the amount of nitrogen in the inhibitor, the inhibitor concentration and the inhibitor molecular weight.

Conclusions

Inhibition efficiencies of 96 and 92% were achieved with BZ4 and BZ3, respectively, at the maximum tested concentration. Density functional theory calculations of BZ3 and BZ4 were performed to compare the effects of hydroxyl and N,N-dimethylamino substituents on the inhibition efficiency, providing insight for designing new molecular structures that exhibit enhanced inhibition efficiencies.