Experimental and theoretical investigation on the anti-corrosion characteristics of pyridine-substituted benzothiazole derivatives for mild steel in aqueous HCl.

Three new 2-(2-pyridyl)benzothiazole derivatives, namely 2-(benzothiazol-2-yl)pyridin-3-amine (APYBT), 2-(benzothiazol-2-yl)pyridin-5-ol (HPYBT) and 2-(pyridin-2-yl)benzothiazole (PYBT), have been synthesized. Those are tested for their potentiality to impart corrosion resistance to mild steel exposed to 1 M aqueous HCl. Both electrochemical and gravimetric experiments establish the studied benzothiazole (BT) derivatives as promising corrosion inhibitors, with APYBT standing out as the most effective one exerting more than 97% inhibition efficiency at 1 mM concentration. PYBT exerts the least inhibitory performance. The electron donating property of the amine group present on the pyridine moiety in APYBT could be responsible for the superiority of APYBT as a corrosion inhibitor among the three. A potentiodynamic polarization study revealed that the inhibitors could retard both the cathodic and anodic reactions. The adsorption of the inhibitors on metal surfaces follows the Langmuir adsorption isotherm. SEM images provide visual confirmation of the protection of mild steel surfaces from corrosion in the presence of the studied benzothiazole (BT) derivatives. The interaction pattern between the mild steel and the inhibitors is explored using results derived from density functional theory (DFT) calculations. Variation of the interaction energy as obtained from molecular dynamics (MD) simulation confirms the corrosion inhibitory trend. Fukui index calculation enables the role played by the substituent group towards the relative electron donation/acceptance properties of the atoms present at the different parts of the inhibitor molecule.

Adsorption and anti-corrosion characteristics of vanillin Schiff bases on mild steel in 1 M HCl: experimental and theoretical study.

Herein, two Schiff base derivatives of vanillin and divanillin with 2-picolylamine, namely, 2-methoxy-4-((pyridin-2-ylmethylimino)methyl)phenol (compound A) and 3,3'-dimethoxy-5,5'-bis-((pyridin-2-ylmethylimino)methyl)-[1,1'-biphenyl]-2,2'-diol (compound B), respectively, were synthesized. Additionally, their adsorption characteristics and corrosion inhibition behavior were compared for mild steel in 1 M HCl using electrochemical impedance spectroscopy, potentiodynamic polarization and weight loss methods. Compound B was found to impart a better anti-corrosive effect (around 95% inhibition efficiency at 313 K) than compound A. The inhibitors act as effective mixed-type inhibitors and exhibit Langmuir-type adsorption behaviour. The kinetic-thermodynamic parameters together with the data obtained from density functional theory (DFT) and molecular dynamics (MD) simulations illustrate the mechanism of corrosion and mode of adsorption of both inhibitors on the metal surface. The better corrosion mitigation propensity of the dimeric form of the inhibitor (compound B) over the monomeric form (compound A) was tested experimentally and explained according to the theoretical data.

Newly synthesized quercetin derivatives as corrosion inhibitors for mild steel in 1 M HCl: combined experimental and theoretical investigation.

To evaluate the corrosion inhibition efficacy of the derivatives of naturally available organics, mono and di-4-((2-hydroxyethyl)piperazin-1-yl)methyl derivatives of quercetin, a flavonoid, have been synthesized. Their potential as anti-corrosive agents is assessed for mild steel in 1 M HCl employing the weight-loss technique as well as electrochemical methods. Comparing the rate of corrosion in uninhibited and inhibited solutions as a function of temperature, the thermodynamic parameters of adsorption of these derivatives on mild steel surfaces and the kinetic parameters of the corrosion process are evaluated. These parameters together with information derived from electrochemical methods are further used to ascertain the mechanism of corrosion and mode of adsorption of inhibitors with intricate detail. Density functional theory (DFT) calculations were employed to explain the relative corrosion inhibition propensity between the studied mono and di quercetin derivatives. Molecular dynamics (MD) simulations were carried out to obtain the interaction energy between the inhibitor molecules and the metal surface. Results show that both derivatives, acting as mixed-type inhibitors, exert profound anti-corrosive influence (around 95% inhibition efficiency at 1 mM concentration at 313 K). Theoretical studies suggest that the trihydroxy chromone ring and dihydroxy phenyl ring of quercetin maintain a planar orientation with respect to each other and are adsorbed on the metal surface (mostly chemisorption).

Novel Schiff-base molecules as efficient corrosion inhibitors for mild steel surface in 1 M HCl medium: experimental and theoretical approach.

In order to evaluate the effect of the functional group present in the ligand backbone towards corrosion inhibition performances, three Schiff-base molecules namely, (E)-4-((2-(2,4-dinitrophenyl)hydrazono)methyl)pyridine (L(1)), (E)-4-(2-(pyridin-4-ylmethylene)hydrazinyl)benzonitrile (L(2)) and (E)-4-((2-(2,4-dinitrophenyl)hydrazono)methyl)phenol (L(3)) were synthesized and used as corrosion inhibitors on mild steel in 1 M HCl medium. The corrosion inhibition effectiveness of the studied inhibitors was investigated by weight loss and several sophisticated analytical tools such as potentiodynamic polarization and electrochemical impedance spectroscopy measurements. Experimentally obtained results revealed that corrosion inhibition efficiencies followed the sequence: L(3) > L(1) > L(2). Electrochemical findings showed that inhibitors impart high resistance towards charge transfer across the metal-electrolyte interface and behaved as mixed type inhibitors. Scanning electron microscopy (SEM) was also employed to examine the protective film formed on the mild steel surface. The adsorption as well as inhibition ability of the inhibitor molecules on the mild steel surface was investigated by quantum chemical calculation and molecular dynamic (MD) simulation. In quantum chemical calculations, geometry optimized structures of the Schiff-base inhibitors, electron density distribution in HOMO and LUMO and Fukui indices of each atom were employed for their possible mode of interaction with the mild steel surfaces. MD simulations revealed that all the inhibitors molecules adsorbed in parallel orientation with respect to the Fe(110) surface.

Adsorption and corrosion inhibition effect of Schiff base molecules on the mild steel surface in 1 M HCl medium: a combined experimental and theoretical approach.

Corrosion inhibition performance of 2-(2-hydroxybenzylideneamino)phenol (L(1)), 2-(5-chloro-2-hydroxybenzylideneamino)phenol (L(2)) and 2-(2-hydroxy-5-nitrobenzylideneamino)phenol (L(3)) on the corrosion behaviour of mild steel surface in a 1 M hydrochloric acid (HCl) solution is investigated by sophisticated analytical methods like potentiodynamic polarization, electrochemical impedance spectroscopy and weight loss measurements. Polarization studies showed that all the compounds are mixed type (cathodic and anodic) inhibitors and the inhibition efficiency (η%) increased with increasing inhibitor concentration. The inhibition actions of these Schiff base molecules are discussed in view of blocking the electrode surface by means of adsorption of the inhibitor molecule obeying the Langmuir adsorption isotherm. Scanning electron microscopy (SEM) studies of the metal surfaces confirmed the existence of an adsorbed film. Density functional theory (DFT) and molecular dynamics (MD) simulation have been used to determine the relationship between molecular configuration and their inhibition efficiencies. The order of inhibition performance obtained from experimental results is successfully verified by DFT and MD simulation.

Conserved water-mediated H-bonding dynamics of catalytic His159 and Asp158: insight into a possible acid-base coupled mechanism in plant thiol protease.

Cysteine protease is ubiquitous in nature. Excess activity of this enzyme causes intercellular proteolysis, muscle tissue degradation, etc. The role of water-mediated interactions in the stabilization of catalytically significant Asp158 and His159 was investigated by performing molecular dynamics simulation studies of 16 three-dimensional structures of plant thiol proteases. In the simulated structures, the hydrophilic W(1), W(2) and WD(1) centers form hydrogen bonds with the OD1 atom of Asp158 and the ND1 atom of His159. In the solvated structures, another water molecule, W(E), forms a hydrogen bond with the NE2 atom of His159. In the absence of the water molecule W(E), Trp177 (NE1) and Gln19 (NE2) directly interact with the NE2 atom of His159. All these hydrophilic centers (the locations of W(1), W(2), WD(1), and W(E)) are conserved, and they play a critical role in the stabilization of His-Asp complexes. In the water dynamics of solvated structures, the water molecules W(1) and W(2) form a water...water hydrogen-bonded network with a few other water molecules. A few dynamical conformations or transition states involving direct (His159 ND1...Asp158 OD1) and water-mediated (His159 ND1...W(2)...Asp158 OD1) hydrogen-bonded complexes are envisaged from these studies.

Conserved water-mediated H-bonding dynamics of catalytic Asn 175 in plant thiol protease.

The role of invariant water molecules in the activity of plant cysteine protease is ubiquitous in nature. On analysing the 11 different Protein DataBank (PDB) structures of plant thiol proteases, the two invariant water molecules W1 and W2 (W220 and W222 in the template 1PPN structure) were observed to form H-bonds with the O b atom of Asn 175. Extensive energy minimization and molecular dynamics simulation studies up to 2 ns on all the PDB and solvated structures clearly revealed the involvement of the H-bonding association of the two water molecules in fixing the orientation of the asparagine residue of the catalytic triad. From this study,it is suggested that H-bonding of the water molecule at the W1 invariant site better stabilizes the Asn residue at the active site of the catalytic triad.