Experimental and theoretical studies on some amino acids and their potential activity as inhibitors for the corrosion of mild steel, part 2

Effects of L-ascorbic acid (C6H8O6: Vit-C) on collagen amino acids: DFT study

Vitamin C plays a very important role in the repair of connective tissue, especially for sports whose training causes the most damage to this tissue. Therefore, many people believe that L-ascorbic acid (C6H8O6: vitamin C) reduces the recovery time between sports exercises. The most abundant form of structural protein in the body is collagen. Collagen is characterized by a high concentration of the three amino acids glycine (Gly), proline (Pro), and hydroxyproline (Hyp), which creates its characteristic triple helix structure. Therefore, in this study, the effect of vitamin C presence on the sequence, interaction, and orientation of amino acids for collagen formation is investigated using computational simulation. This study aimed to investigate the mechanism of action of vitamin C in terms of thermodynamics and structure of the reaction. The calculations are performed using density function theory (DFT) by the base set of B3LYP/6-311++G (p,d). The results show that the presence of vitamin C is effective in the formation of collagen protein for this interaction and the mechanism of amino acid sequence (Gly-Hyp-Pro) is better in the formation of collagen protein in the presence of vitamin C. The presence of Vit-C in the formation and direction of hydroxyproline (Hyp) causes its separation from the prolyl 5-hydroxylase enzyme. In the absence of vitamin C, the reaction stops at this stage and proline cannot be converted into hydroxyproline. The computational data shows vitamin C prevents unwanted interactions and directs amino acid reactions to repair connective tissue (collagen). Therefore, vitamin C acts as a cofactor in the Prolyl 5-Hydroxylase enzyme and causes it to convert proline to hydroxyl.

Selective detection of nitrotyrosine using dual-fluorescent carbon dots

The post-translational modification of amino acid plays a critical role in normal and diseased biological states. Specifically, nitrotyrosine (nTyr) has been linked to diseases, including neurodegeneration, among others. Hence, alternative methods are required for detection and differentiation of nTyr from other structurally similar analogues, such as Tyrosine (Tyr) or phosphotyrosine (pTyr). Herein, the selective detection of nTyr, over other congeners, was achieved by using dual-fluorescent carbon dots (CDs) in buffered solution, artificial saliva, bovine serum albumin and diluted equine serum. The nTyr induced fluorescence quenching of the blue and red emissions of CDs, in the 20-105 μM linear range, and with the limit of detection (LOD) at 34 μM, which was well below the physiological concentration required for detection. The sensor was functional at biological pH values, with optimal quenching efficiency at basic pH. The sensor was highly selective for nTyr even in the presence of common biological interferences (metal cations, organic anions, amino acids, nucleosides and other biologicals). The mechanism of quenching (a combination of static and dynamic) was ascribed to the nonradiative energy transfer, due to electronic overlap between nTyr absorbance and CDs fluorescence emission, and electron transfer from excited CDs state to nTyr as an electron acceptor. The dual-fluorescent CDs represent viable sensors for key biological modifications, and their selectivity and sensitivity may be further improved through tailored chemical synthesis of CDs, such as tunable surface chemistry to promote selective recognition of analyte of interest.

A Brief Review on Fruit and Vegetable Extracts as Corrosion Inhibitors in Acidic Environments

The corrosion of metals, i.e., the initiation and acceleration of the surface deterioration of metals through an electrochemical reaction with the surrounding intrusive environment, is a global concern because of the economic and environmental impacts. Corrosion inhibitors are considered the most practical choice among the available corrosion protection techniques due to their effectiveness in terms of functionality and cost. The use of traditional and toxic corrosion inhibitors has led to environmental issues, arousing the need for green counterparts that are environmentally friendly, easily accessible, biodegradable, and cost-effective. In this review, the utilization of green corrosion inhibitors purely acquired from renewable sources is explored, with an in-depth focus on the recent advancements in the use of fruit and vegetable extracts as green corrosion inhibitors. In particular, fruits and vegetables are natural sources of various phytochemicals that exhibit key potential in corrosion inhibition. To shed light on the true potential of such extracts in the protection of steel in acidic environments, the experimental techniques involved in corrosion inhibition and the mechanism of corrosion inhibition are discussed in detail. The study highlights the potential of fruit and vegetable extracts as non-toxic, economical, and effective corrosion inhibitors in the pursuit of green chemistry. In addition to discussing and outlining the current status and opportunities for employing fruit and vegetable extracts as corrosion inhibitors, the current review outlines the challenges involved in the utilization of such extracts in corrosion inhibition.

Synthesis of TiO2 nanogel composite for highly efficient self-healing epoxy coating

INTRODUCTION

Organic coatings are the most effective and facile methods of protecting steel against corrosion, which shields it from direct contact with oxygen and moisture. However, they are inherently defective and susceptible to damage, which allows the penetration of the corrosive media into the underlying substrates. Self-healing coatings were developed to address this shortcoming.

OBJECTIVE

The current research aims to develop a coating with superior self-healing ability via embedment of titanium dioxide (TiO₂) nanogel composite (NC) in a commercial epoxy.

METHODS

The TiO₂ NC was prepared by efficient dispersion of TiO₂ nanoparticles in copolymer gel of acrylamide (AAm) and 2-acrylamido-2-methyl propane sulfonic acid (AMPS) with the help of 3-(trimethoxysilyl) propyl methacrylate (MPS). The chemical structure, morphology, and thermal properties of the modified and functionalized nanoparticles were assessed by infrared spectroscopy, electron microscopy, X-ray diffraction, and thermogravimetric analysis, respectively. In addition, TiO₂ nanoparticles, nano-TiO₂ functionalized monomer (NTFM), and NTFM/AAm/AMPS in different weight percentages were incorporated into epoxy resin to prepare a self-healing coating.

RESULTS

The results confirmed the successful fabrication of the NC. In addition, the incorporation of 1 wt% NTFM/AAm/AMPS led to homogenous dispersion, enhanced anti-corrosive and self-healing performance with the healing efficiencies of 100% and 98%, which were determined by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization methods, respectively.

CONCLUSION

The prepared NC was sensitive towards salt concentration, pH, which aids the quick reaction of the TiO₂ NC to corrosive ions, once the cracks occur. In addition, this is a unique feature compared to the other self-healing mechanisms, especially, the encapsulation of healing agents, which can be effective as long as the healing agent is present.

Comparative Gravimetric Studies on Carbon Steel Corrosion in Selected Fruit Juices and Acidic Chloride Media (HCl) at Different pH

Food contamination due to metal corrosion and the consequent leakage of metals into foods is a problem. Understanding the mechanism(s) of metal corrosion in food media is vital to evaluating, mitigating, and predicting contamination levels. Fruit juices have been employed as model corrosive media to study the corrosion behaviour of metallic material in food media. Carbon steel corrosion in fresh juices of tomato, orange, pineapple, and lemon, as well as dilute hydrochloric acid solutions at varied pH, was studied using scanning electron microscopy, gravimetric and spectrophotometric techniques, and comparisons made between the corrosivity of these juices and mineral acids of comparable pH. The corrosion of carbon steel in fruit juices and HCl solutions manifests as a combination of uniform and pitting corrosion. Gravimetric data acquired after one hour of immersion at ambient temperature (22 °C) indicated corrosion rates of 0.86 mm yr^-1 in tomato juice (pH ≈ 4.24), 1.81 mm yr^-1 in pineapple juice (pH ≈ 3.94), 1.52 mm yr^-1 in orange juice (pH ≈ 3.58), and 2.89 mm yr^-1 in lemon juice (pH ≈ 2.22), compared to 2.19 mm yr^-1 in 10^-2 M HCl (pH ≈ 2.04), 0.38 mm yr^-1 in 10^-3 M HCl (pH ≈ 2.95), 0.17 mm yr^-1 in 10^-4 M HCl (pH ≈ 3.95), and 0.04 mm yr^-1 in 10^-5 M HCl (pH ≈ 4.98). The correlation of gravimetrically acquired corrosion data with post-exposure spectrophotometric analysis of fruit juices enabled de-convolution of iron contamination rates from carbon steel corrosion rates in fruit juices. Elemental iron contamination after 50 h of exposure to steel samples was much less than the values predicted from corrosion data (≈40%, 4.02%, 8.37%, and 9.55% for tomato, pineapple, orange, and lemon juices, respectively, relative to expected values from corrosion (weight loss) data). Tomato juice (pH ≈ 4.24) was the least corrosive to carbon steel compared to orange juice (pH ≈ 3.58) and pineapple juice (pH ≈ 3.94). The results confirm that though the fruit juices are acidic, they are generally much less corrosive to carbon steel compared to hydrochloric acid solutions of comparable pH. Differences in the corrosion behaviour of carbon steel in the juices and in the different mineral acid solutions are attributed to differences in the compositions and pH of the test media, the nature of the corrosion products formed, and their dissolution kinetics in the respective media. The observation of corrosion products (iron oxide/hydroxide) in some of the fruit juices (tomato, pineapple, and lemon juices) in the form of apparently hollow microspheres indicates the feasibility of using fruit juices and related wastes as "green solutions" for the room-temperature and hydrothermal synthesis of metal oxide/hydroxide particles.

Evaluation of extracellular polymeric substances extracted from waste activated sludge as a renewable corrosion inhibitor

Background

Waste activated sludge (WAS) has recently gained attention as a feedstock for resource recovery. The aim of this study is to investigate the corrosion inhibition efficiencies of extracellular polymeric substances (EPS) extracted from WAS.

Methods

The studied corrosion inhibitors were tested with carbon steel in 3.64% NaCl saturated with CO₂ at 25 °C, which is the typical oilfield environment. They were first prepared by EPS extraction (heating at 80 °C), followed by centrifugation for solid and liquid separation, then the supernatant was freeze-thawed five times for sterilization of microorganisms in WAS to terminate metabolic activities in the test inhibitors to ensure consistency in corrosion inhibition. The EPS mixture (supernatant) was then deemed as the test corrosion inhibitor. The inhibition performance was determined using potentiodynamic polarization scans.

Results

Waste activated sludge alone showed unsatisfactory inhibition. However, EPS extracted from WAS showed an optimum inhibition of approximately 80% with 1,000 mg/L of inhibitor. The average total solid (TS) and EPS contents of the WAS were 7,330 mg TS/L WAS and 110 mg EPS/g TS, respectively. Three sets of extracted EPS were scanned with fourier-transform infrared spectroscopy (FTIR) and showed almost overlapping curves, yielding the consistent inhibition performance.

Discussion

The potentiodynamic polarization results indicated that EPS acts as a mixed-type inhibitor which inhibits corrosion on both anode and cathode sites of metal surfaces. Based on the FTIR results, it was assumed that major chemical groups O–H, N–H, C–N, C=O, and C–H contributed to the inhibition by adsorbing on the metal surface, forming a biofilm that acts as a protective barrier to isolate the metal from its corrosive environment. Results show that WAS EPS corrosion inhibitors have inhibition performance comparable to commercial products, signifying their potential in commercialization. This corrosion inhibitor is renewable, biodegradable, non-toxic, and free from heavy metal, making it a superior green corrosion inhibitor candidate. Additionally, turning biomass into value-added product can be beneficial to the environment and, in this case, deriving new materials from WAS could also transform the economics of wastewater treatment operations.

Corrosion Inhibition of Mild Steel by Poly(butylene succinate)-L-histidine Extended with 1,6-diisocynatohexane Polymer Composite in 1 M HCl

The ecofriendly poly(butylene succinate) extended with 1,6-diisocynatohexane composted with L-histidine (PBSLH) polymer composite was synthesized by condensation polymerization. The polymer composite was characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD), and scanning electron microscope (SEM-EDX). The inhibition action of the polymer composite was investigated by conventional weight loss, potentiodynamic polarization, variable amplitude micro (VASP), and electrochemical impedance spectroscopy (EIS). The maximum corrosion inhibition efficiency of 78 % was obtained at concentration level of 600 ppm. The results revealed PBSLH as a mixed type corrosion inhibitor. The thermodynamic and kinetic parameters also revealed adsorption of PBSLH on to mild surface as exothermic and the adsorption was conformed to Langmuir model. The morphology of mild steel coupons was investigated by SEM and atomic force microscope (AFM) and the results showed PBSLH to have inhibited corrosion on mild steel in 1 M HCL.

A theoretical study of 5,6,7,8-tetrahydro-6-hydroxymethylpterin: insight into intrinsic photoreceptor properties of 6-substituted tetrahydropterins

Tetrahydropterins are essential biological cofactors, which play a crucial role in DNA and RNA syntheses, NO synthesis, hydroxylation of aromatic amino acids, etc. In the last few years, it has been shown that 6-substituted "unconjugated" tetrahydropterins can also play a photoreceptor chromophoric role in plants and cyanobacteria. However, the nature of the initial light signal transduction act in which H4pterins participate is unknown. Our quantum chemical calculations have shown the possibility of the fast internal conversion of excited states of H4pterins. The potential energy surface scan along the 1ππ* state shows no energy barrier leading to 1ππ*/S0 conical intersection, this explains the absence of fluorescence for H4pterins. Other trajectories of the internal conversion relate to the stretching vibrations of the N-H bonds of the pyrimidine ring for the Rydberg state. The presence of several trajectories of nonradiative quenching of the photoexcited singlet states provides the photostability of the molecule. It was demonstrated for the first time that the nature of the excited states of H4pterins is similar to the nature of the excited states of guanine.

Computational chemistry study of toxicity of some m-tolyl acetate derivatives insecticides and molecular design of structurally related products

Molecular descriptors (including quantum chemical, topological and physicochemical descriptors) were calculated for five m-tolyl derivatives insecticides [namely, carbosulfan (CBS), carbofuran (CBF), isoprocab (IFP), methiocarb (MTC) and isocarbophos (ICP)]. Calculated quantum chemical parameters included the total energy, the electronic energy, the binding energy, the core-core repulsion energy, the heat of formation, the dipole moment and the frontier molecular orbital energies. All the calculated quantum chemical parameters (except dipole moment) exhibited strong correlation with the experimental LD₅₀ values of the studied insecticides (at various Hamiltonians). Calculated topological parameters included the molecular topological index (MTI), polar surface area (PSA), total connectivity (TC), total valence connectivity (TVC), Wiener index (WI), topological diameter (TD) and Balaban index (BI). However, only MTI, PSA, WI and BI exhibited excellent correlation with the toxicological activity of the insecticides. Also among all the calculated physicochemical parameters [logP, surface area (SA), surface volume (SV), hydration energy (E_Hydr), polarizability (PLZ) and refractivity (RFT)], only SV, E_Hydr, PLZ and RFT were useful in establishing quantitative structure activity relationship (QSAR). Application of QSAR indicated that the calculated theoretical LD₅₀ values for the studied insecticides displayed excellent correlation with experimentally derived LD₅₀ values. However, best results were obtained from quantum chemical descriptors under modified neglect of atomic overlap (MNDO). The toxicity profile of the insecticides also correlated strongly with ionization energy, electron affinity, global softness and global harness. Reactive sites of each of the insecticides were established using Fukui function, Huckel charges and HOMO/LUMO diagrams. Six new molecules were proposed and their theoretical activities were estimated. The proposed molecules included 2-methyl-2-(methylthio)-2,3-dihydrobenzofuran-7-yl methylcarbamate, O-methyl O-2-((methylaminooxy)carbonyl)phenyl phosphoramidothioate, 2-((methylaminooxy)carbonyl)phenyl methylcarbamate, 2-(1-(methylthio)ethyl)phenyl methylcarbamate, N-methyl-O-(2-(methylthiooxy) benzoyl) hydroxyl amine and 4-methyl naphthalen-2-yl methylcarbamate. Some of the proposed molecules exhibited negative values of LD₅₀ (indicating extreme toxicity) while two of them exhibited values that are comparable to existing insecticides.

Corrosion inhibition performance of newly synthesized 5-alkoxymethyl-8-hydroxyquinoline derivatives for carbon steel in 1 M HCl solution: experimental, DFT and Monte Carlo simulation studies

Three new organic compounds primarily based on 8-hydroxyquinoline have been successfully synthesized and characterized via different spectroscopic methods (FTIR, ¹H, and ¹³C NMR).

A composite additive used for a new cyanide-free silver plating bath (II): an insight by electrochemical measurements and quantum chemical calculation

BPY and PAT are effective additives for silver plating due to their ability for strong adsorption on silver surfaces.

Synthesis, biological evaluation and docking studies of some novel isatin-3-hydrazonothiazolines

The putative binding mode of compound 6i in the active site of Jack bean urease.

Synthesis, cytotoxic and urease inhibitory activities of some novel isatin-derived bis-Schiff bases and their copper(ii) complexes

The putative binding mode of the most active compound 3b in the active site of Jack bean urease.

A new insight into resource recovery of excess sewage sludge: feasibility of extracting mixed amino acids as an environment-friendly corrosion inhibitor for industrial pickling

The work mainly presented a laboratory-scale investigation on an effective process to extract a value-added product from municipal excess sludge. The functional groups in the hydrolysate were characterized with Fourier transform infrared spectrum, and the contained amino acids were measured by means of an automatic amino acid analyzer. The corrosion-inhibition characteristics of the hydrolysate were determined with weight-loss measurement, electrochemical polarization and scanning electron microscopy. Results indicated that the hydrolysate contained 15 kinds of amino acid, and their adsorption on the surface could effectively inhibit the corrosion reaction of the steel from the acid medium. Polarization curves indicated that the obtained hydrolysate was a mixed-type inhibitor, but mainly restricted metal dissolution on the anode. The adsorption accorded well with the Langmuir adsorption isotherm, involved an increase in entropy, and was a spontaneous, exothermic process.

Theoretical and experimental studies on the corrosion inhibition potentials of some purines for aluminum in 0.1 M HCl

Experimental aspect of the corrosion inhibition potential of adenine (AD), guanine (GU) and, hypoxanthine (HYP) was carried out using weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods while the theoretical aspect of the work was carried out by calculations of semi-empirical parameters (for AM1, MNDO, CNDO, PM3 and RM1 Hamiltonians), Fukui functions and inhibitor–metal interaction energies. Results obtained from the experimental studies were in good agreement and indicated that adenine (AD), guanine (GU) and hypoxanthine (HYP) are good adsorption inhibitors for the corrosion of aluminum in solutions of HCl. Data obtained from electrochemical experiment revealed that the studied purines functioned by adsorption on the aluminum/HCl interface and inhibited the cathodic half reaction to a greater extent and anodic half reaction to a lesser extent. The adsorption of the purines on the metal surface was found to be exothermic and spontaneous. Deviation of the adsorption characteristics of the studied purines from the Langmuir adsorption model was compensated by the fitness of Flory Huggins and El Awardy et al. adsorption models. Quantum chemical studies revealed that the experimental inhibition efficiencies of the studied purines are functions of some quantum chemical parameters including total energy of the molecules (TE), energy gap (E_L–H), electronic energy of the molecule (EE), dipole moment and core–core repulsion energy (CCR). Fukui functions analysis through DFT and MP2 theories indicated slight complications and unphysical results. However, results obtained from calculated Huckel charges, molecular orbital and interaction energies, the adsorption of the inhibitors proceeded through the imine nitrogen (N5) in GU, emanine nitrogen (N7) in AD and the pyridine nitrogen (N5) in HPY.

Corrosion Inhibition Effect of Carbon Steel in Sea Water by L-Arginine-Zn2+System

The inhibition efficiency of L-Arginine-Zn2+system in controlling corrosion of carbon steel in sea water has been evaluated by the weight-loss method. The formulation consisting of 250 ppm of L-Arginine and 25 ppm of Zn2+has 91% IE. A synergistic effect exists between L-Arginine and Zn2+. Polarization study reveals that the L-Arginine-Zn2+system functions as an anodic inhibitor and the formulation controls the anodic reaction predominantly. AC impedance spectra reveal that protective film is formed on the metal surface. Cyclic voltammetry study reveals that the protective film is more compact and stable even in a 3.5% NaCl environment. The nature of the protective film on a metal surface has been analyzed by FTIR, SEM, and AFM analysis.

Theoretical and experimental studies of the corrosion inhibition effect of nitrotetrazolium blue chloride on copper in 0.1 M H2SO4

Theoretical and experimental studies of the corrosion inhibition effect of nitrotetrazolium blue chloride on copper in 0.1 M H₂SO₄.

6-bromoisatin found in muricid mollusc extracts inhibits colon cancer cell proliferation and induces apoptosis, preventing early stage tumor formation in a colorectal cancer rodent model

Muricid molluscs are a natural source of brominated isatin with anticancer activity. The aim of this study was to examine the safety and efficacy of synthetic 6-bromoisatin for reducing the risk of early stage colorectal tumor formation. The purity of 6-bromoisatin was confirmed by ¹H NMR spectroscopy, then tested for in vitro and in vivo anticancer activity. A mouse model for colorectal cancer was utilized whereby colonic apoptosis and cell proliferation was measured 6 h after azoxymethane treatment by hematoxylin and immunohistochemical staining. Liver enzymes and other biochemistry parameters were measured in plasma and haematological assessment of the blood was conducted to assess potential toxic side-effects. 6-Bromoisatin inhibited proliferation of HT29 cells at IC₅₀ 223 μM (0.05 mg/mL) and induced apoptosis without increasing caspase 3/7 activity. In vivo 6-bromoisatin (0.05 mg/g) was found to significantly enhance the apoptotic index (p ≤ 0.001) and reduced cell proliferation (p ≤ 0.01) in the distal colon. There were no significant effects on mouse body weight, liver enzymes, biochemical factors or blood cells. However, 6-bromoisatin caused a decrease in the plasma level of potassium, suggesting a diuretic effect. In conclusion this study supports 6-bromoisatin in Muricidae extracts as a promising lead for prevention of colorectal cancer.

Studies on 2-arylhydrazononitriles: synthesis of 3-aryl-2-arylhydrazopropanenitriles and their utility as precursors to 2-substituted indoles, 2-substituted-1,2,3-triazoles, and 1-substituted pyrazolo[4,3-d]pyrimidines

Coupling of 2-benzylmalononitrile with aromatic diazonium salts afforded 3-phenyl-2-arylhydrazonopropanenitriles 4a,b, which were rearranged into 2-cyanoindoles 5a,b upon heating with ZnCl(2) in the presence of glacial acetic acid. The produced indole derivatives 5a,b can be successfully used as valuable precursors to synthesize 1,2,4-oxadiazolylindoles 8a,b. The reaction of arylhydrazononitriles 4a,b with hydroxylamine afforded an amidoximes 9a,b that could be cyclized into 1,2,3-triazole-4-amines 10a,b. In addition, 4a,b could be converted into 4-aminopyrazoles 12a,b via condensation with chloroacetonitrile in the presence of triethylamine as a basic catalyst. Finally, compounds 12a,b were refluxed with dimethylformamide dimethylacetal (DMFDMA) to afford amidines 13a,b that were readily cyclized to the corresponding pyrazolo[4,3-d]pyrimidines 14a,b when refluxed with ammonium acetate.