Syntheses of coumarins, which are a structurally interesting antioxidant activity, was done in this article. The modification of 7-hydroxycoumarin by different reaction steps was done to yield target compounds. Molecular structures were characterized by different spectroscopical techniques (Fourier transformation infrared and nuclear magnetic resonance). Antioxidant activities were performed by using various in vitro spectrophometric assays against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and hydrogen peroxide (H 2 O 2 ). All compounds exhibited high efficiency as antioxidants compared to ascorbic acid. The highest efficiency scavenging activity was found for compound 3 (91.0˘5.0), followed by compounds 2 and 4 (88.0˘2.00; and 87.0˘3.00). Ascorbic acid C was used as a standard drug with a percentage inhibition of 91.00˘1.5. The mechanism of the synthesized compounds as antioxidants was also studied. Hartree-Fock-based quantum chemical studies have been carried out with the basis set to 3-21G, in order to obtain information about the three-dimensional (3D) geometries, electronic structure, molecular modeling, and electronic levels, namely HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital), to understand the antioxidant activity for the synthesized compounds.
Background
The acid corrosion inhibition process of mild steel in 1 M HCl by 4-[(2-amino-1, 3, 4-thiadiazol-5-yl)methoxy]coumarin (ATC), has been investigated using weight loss technique and scanning electron microscopy (SEM). ATC was synthesized, and its chemical structure was elucidated and confirmed using spectroscopic techniques (infrared and nuclear magnetic resonance spectroscopy).FindingsThe results indicated that inhibition efficiencies were enhanced with an increase in concentration of inhibitor and decreased with a rise in temperature. The adsorption equilibrium constant (K) and standard free energy of adsorption (ΔGads) were calculated. Quantum chemical parameters such as highest occupied molecular orbital energy, lowest unoccupied molecular orbital energy (EHOMO and ELUMO, respectively) and dipole moment (μ) were calculated and discussed. The results showed that the corrosion inhibition efficiency increased with an increase in both the EHOMO and μ values but with a decrease in the ELUMO value.ConclusionsOur research show that the synthesized macromolecule represents an excellent inhibitor for materials in acidic solutions. The efficiency of this macromolecule had maximum inhibition efficiency up to 96 % at 0.5 mM and diminishes with a higher temperature degree, which is revealing of chemical adsorption. An inhibitor molecule were absorbed by metal surface and follow Langmuir isotherms low and establishes an efficient macromolecule inhibitor having excellent inhibitive properties due to entity of S (sulfur) atom, N (nitrogen) atom and O (oxygen) atom.
The corrosion inhibition of Schiff base, namely 2-((2-hydroxy-5-methoxybenzylidene)amino)pyridine (HMAP), for mild steel (MS) in a 1 M hydrochloric acid environment was investigated by means of weight loss and scanning electron microscopy techniques. Quantum chemical calculation based on density functional theory (DFT) was carried out on HMAP. Results illustrated that HMAP is a superior inhibitor for the corrosion of MS in 1.0M hydrochloric acid environment, and inhibition efficiency is higher than 90.0% at 0.5 g/L HMAP. Inhibition performance increases with regard to concentration increase and inhibition performance decreases when raising temperature. Adsorption of the inhibitor on the MS surface followed Langmuir adsorption isotherm and the value of the free energy of adsorption; ΔGads indicated that the adsorption of HMAP was a physisorption/chemisorption process. The DFT refers to perfect correlation with methodological inhibition performance.
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