• Korean Journal of Metals and Materials
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• v.47 no.7
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• pp.423-432
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• 2009

In the galvanizing coating process, the effects of the silicon content on the coatability and wettability of molten zinc were investigated on Dual-Phase High Strength Steels (DP-HSS) with various Si contents using the galvanizing simulator and dynamic reactive wetting systems. DP-HSS showed good coatability and a well-developed inhibition layer in the range of Si content below 0.5 wt%. Good coatability was the results of the mixed oxide $Mn_{2}SiO_{4}$, being formed by the selective oxidation on the surface, with a low contact angle in molten zinc and a large fraction of oxide free surface that provided a sufficient site for the molten zinc to wet and react with the substrate. On the other hand, with more than 0.5 wt%, DP-HSS exhibited poor coatability and an irregularly developed inhibition layer. The poor coatability was due to the poor wettability that resulted from the development of network-type layers of amorphous ${SiO}_{2}$, leading to a high contact angle in molten zinc, on the surface.

• Journal of Electrochemical Science and Technology
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• v.10 no.1
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• pp.29-36
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• 2019

Corrosion inhibition by synthesised ligand, 2-acetylpyridine 4-ethyl-3-thiosemicarbazone (HAcETSc) and its tin(IV) complex, dichlorobutyltin(IV) 2-acetylpyridine 4-ethyl-3-thiosemicarbazone ($Sn(HAcETSc)BuCl_2$) on mild steel in 1 M hydrochloric acid (HCl) was studied using weight loss measurement, potentiodynamic polarisation, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). The inhibition efficiency increases by increasing the inhibitor concentrations. The polarisation study showed that both synthesised compounds were mixed type inhibitors. The electrochemical impedance study showed that the presence of inhibitors caused the charge transfer resistance to increase as the concentration of inhibitors increased. The adsorption of these compounds on mild steel surface was found to obey Langmuir's adsorption isotherm with the free energy of adsorption ${\Delta}G{^o}_{ads}$ of -3.7 kJ/mol and -7.7 kJ/mol for ligand and complex respectively, indicating physisorption interaction between the inhibitors and 1 M HCl solution.

• Corrosion Science and Technology
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• v.21 no.6
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• pp.423-433
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• 2022

The objective of this study was to determine whether Cymbopogon citratus extract as a corrosion inhibitor from natural tropical resources could prevent corrosion of carbon steel in sulfuric acid solution. Inhibitory action of this extract was investigated using electrochemical methods such as potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Those methods revealed corrosion rate, efficiency of inhibition, and adsorptions isotherm values when the extract was added to the sulfuric acid solution at concentration up to 500 ppm with various immersion time at ambient temperature. Results revealed that higher concentration of the extract and longer immersion time decreased the corrosion rate of carbon steel whereas the inhibition efficiency of the extract was increased up to 97.25%. The value of charge transfer resistance was increased significantly by adding the extract at concentration up to 500 ppm with an immersion time of 60 minutes. The type of the extract was a mixed inhibitor. It could inhibit the corrosion process in both anodic and cathodic sides electrochemically. Results of this study suggest that the mechanism of adsorption on the surface of carbon steel is related to Langmuir adsorption isotherm.

• Corrosion Science and Technology
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• v.12 no.2
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• pp.65-78
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• 2013

The present investigation deals with the corrosion inhibition of mild steel in 1M $H_2SO_4$ with 1, 4-dihydro pyridine and its derivatives prepared using microwave activation method. The synthesis of inhibitor was confirmed by IR spectra. The effect of 1, 4-dihydropyridine derivatives on the corrosion inhibition of mild steel in 1M $H_2SO_4$ was studied using weight loss and electrochemical polarization techniques. Influence of temperature (303-333K) and synergistic effect of halide ions ($I^-$, $Br^-$ and $Cl^-$) on the inhibition behaviour was also studied. Corrosion products on the metal surface were analyzed by scanning electron microscopy (SEM) and a possible mechanism of inhibition by the compounds is suggested. Thermodynamic parameters were calculated using weight loss data in order to elaborate the mechanism of corrosion inhibition. Polarization measurements revealed that the studied compounds acted as mixed type inhibitor but slightly anodic in nature. Electrochemical impedance measurements revealed that the compounds were adsorbed onto the carbon steel surface and the adsorption obeyed the Langmuir adsorption isotherm. The synergistic effect of halide ions on the IE increases with increase in concentration. The IE obtained from atomic absorption spectrophotometric studies was found to be in good agreement with that obtained from the conventional weight loss method. SEM revealed the information of a smooth, dense protective layer in presence of the inhibitors.

• International Journal of Industrial Entomology and Biomaterials
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• v.9 no.1
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• pp.29-33
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• 2004

Low molecular weight silk fibroin (LMSF), which was prepared by hydrolysis of silk fibroin using high-temperature and high-pressure method, was found to inhibit the oxidation of L-3,4,-dihydroxyphenylalanine (L-DOPA) catalyzed by mushroom tyrosinase (EC 1.14.18.1). LMSF contained mostly free amino acids such as L-glycine, L-alanine, and L-serine and oligopeptides, mainly glycine-alanine dimer. As a result of analyzing the inhibition kinetics from Lineweaver-Burk plots, L-glycine and glycine-alanine dimer showed noncompetitive behavior while uncompetitive behavior was observed in L-alanine, and L-serine. When weight percent concentration of ${ID_50}$ was compared, L-glycine was most effective on the inhibition and LMSF was also good enough for the inhibition effect of tyrosinase activity. LMSF showed a mixed-type inhibition and the inhibitory mechanism of LMSF might be caused by free amino acids and oligopeptides. As a result of spectroscopic observation with time, initial rate of increase of DOPAchrome decreased remarkably and the time to reach maximum absorbance increased as an increase of the concentration of L-glycine, meaning that L-glycine made itself mainly responsible for the formation of chelate with ${Cu^2+}$ in tyrosinase. However, in case of L-alanine, L-serine, and especially glycine-alanine dimmer, the production of DOPAchrome after an arrival at maximum absorbance decreased, indicating the production of adducts through the reaction with DOPAquinone.

• Bulletin of the Korean Chemical Society
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• v.35 no.6
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• pp.1681-1686
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• 2014

A series of hybrid molecules between (${\alpha}$)-lipoic acid (ALA) and 4-amino-1-benzyl piperidines were synthesized and their in vitro cholinesterase (acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE)) inhibitory activities were evaluated. Even though the parent compounds did not exhibit any inhibitory activity against cholinesterase (ChE) with the exception of compound 14 ($IC_{50}=255.26{\pm}4.41$ against BuChE), all hybrid molecules demonstrated BuChE inhibitory activity. Some hybrid compounds also displayed AChE inhibitory activity. Specifically, compound 17 was shown to be an effective inhibitor against both AChE ($IC_{50}=1.75{\pm}0.30{\mu}M$) and BuChE ($IC_{50}=5.61{\pm}1.25{\mu}M$) comparable to galantamine ($IC_{50}=1.7{\pm}0.9{\mu}M$ against AChE and $IC_{50}=9.4{\pm}2.5{\mu}M$ against BuChE). Inhibition kinetic studies using compound 17 indicated a mixed inhibition type for AChE and a noncompetitive inhibition type for BuChE. Its binding affinity ($K_i$) values to AChE and BuChE were $3.8{\pm}0.005{\mu}M$ and $7.0{\pm}0.04{\mu}M$, respectively.

• Microbiology and Biotechnology Letters
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• v.49 no.2
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• pp.217-224
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• 2021

Rice blast caused by Pyricularia oryzae, which is a major threat to food security worldwide, markedly decreases the yield of rice. Some rhizobacteria called 'plant growth-promoting rhizobacteria' inhibit plant pathogens and improve plant growth by secreting iron-chelating siderophores. The decreased availability of iron adversely affects the survival of pathogens, especially fungal pathogens, in the rhizosphere. This study aimed to determine the morphological diversity of siderophore-producing bacteria, analyze the type of siderophores produced by the bacteria, and examine their growth-inhibitory activity against Pyricularia oryzae. The rhizobacteria were isolated from the rhizosphere of Sembada Hitam variety of black rice plants in Pakem, Sleman, Yogyakarta, Indonesia. In total, 12 distinct isolates were screened for the production of siderophores. It was found that 9 out of 12 bacteria produced siderophore and most of them were Gram positive bacteria. The best siderophore-producing isolates with different type of siderophore were used in further studies. The IS3 and IS14 isolates were found to be the best siderophore producer that produced hydroxamate and mixed type of hydroxamate-carboxylate type of siderophore, respectively. In the dual culture assay, IS14 showed a strong antagonistic effect against Pyricularia oryzae by the 81.17% inhibition.

• Bulletin of the Korean Chemical Society
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• v.34 no.4
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• pp.1025-1029
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• 2013

In the previous paper (Bull. Korean Chem. Soc., 2011, 32, 2997), the hybrid molecules between ${\alpha}$-lipoic acid (ALA) and polyphenols (PPs) connected with neutral 2-(2-aminoethoxy)ethanol linker (linker-1) showed new biological activity such as butyrylcholinesterase (BuChE) inhibition. In order to increase the binding affinity of the hybrid compounds to cholinesterase (ChE), the neutral 2-(2-aminoethoxy)ethanol (linker 1) was switched to the cationic 2-(piperazin-1-yl)ethanol linker (linker 2). The $IC_{50}$ values of the linker-2 hybrid molecules for BuChE inhibition were lower than those of linker-1 hybrid molecules (except 9-2) and they also had the same great selectivity for BuChE over AChE (> 800 fold) as linker-1 hybrid molecules. ALA-acetyl caffeic acid (10-2, ALA-AcCA) was shown as an effective inhibitor of BuChE ($IC_{50}=0.44{\pm}0.24{\mu}M$). A kinetic study using 7-2 showed that it is the same mixed type inhibition as 7-1. Its inhibition constant (Ki) to BuChE is $4.3{\pm}0.09{\mu}M$.

• Journal of Electrochemical Science and Technology
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• v.13 no.2
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• pp.237-253
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• 2022

The methyl 2-(1,3-dithietan -2- ylidene)-3-oxobutanoate (MDYO) and 2-(1,3-dithietan-2-ylidene) cyclohexane -1,3-dione (DYCD) were synthesized and tested at various concentrations as corrosion inhibitors for 316L stainless steel in 1 M HCl using weight loss, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), surface analysis techniques (SEM / EDX and Raman spectroscopy) and Functional Density Theory (DFT) was also used to calculate quantum parameters. The obtained results indicated that the inhibition efficiency of MDYO and DYCD increases with their concentration, and the highest value of corrosion inhibition efficiency was determined in the range of concentrations investigated (0.01 × 10^-3 - 10^-3 M). Polarization curves (Tafel extrapolation) showed that both compounds act as mixed-type inhibitors in 1M HCl solutions. Electrochemical impedance spectra (Nyquist plots) are characterized by a capacitive loop observed at high frequencies, and another small inductive loop near low frequencies. The thermodynamic data of adsorption of the two compounds on the stainless steel surface and the activation energies were determined and then discussed. Analysis of experimental results shows that MDYO and DYCD inhibitors adsorb to the metal surface according to the Langmuir model and the mechanism of adsorption of both inhibitors involves physisorption. SEM-EDX results confirm the existence of an inhibitor protective film on the stainless steel surface. The results derived from theoretical calculations supported the experimental observation.

• Bulletin of the Korean Chemical Society
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• v.34 no.11
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• pp.3322-3326
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• 2013

A series of hybrid molecules between (${\alpha}$)-lipoic acid (ALA) and benzyl piperazines were synthesized and their in vitro cholinesterase [acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE)] inhibitory activities were evaluated. Even though the parent compounds did not show any inhibitory activity against cholinesterase (ChE), all hybrid molecules showed BuChE inhibitory activity. Some hybrid compounds also displayed AChE inhibitory activity. Specifically, ALA-1-(3-methylbenzyl)piperazine (15) was shown to be an effective inhibitor of both BuChE ($IC_{50}=2.3{\pm}0.7{\mu}M$) and AChE ($IC_{50}=30.31{\pm}0.64{\mu}M$). An inhibition kinetic study using compound 15 indicated a mixed inhibition type. Its binding affinity ($K_i$) value to BuChE is $2.91{\pm}0.15{\mu}M$.