The inhibition behavior of two pyrimidine-pyrazole derivatives against corrosion in hydrochloric solution: Experimental, surface analysis and in silico approach studies

Mechanistic insight of α-mangostin encapsulation in 2-hydroxypropyl-β-cyclodextrin for solubility enhancement

α-Mangostin is the most abundant compound contained in the mangostin (Garcinia mangostana L.) plant which have been developed and proven to have many promising pharmacological effects. However, the low water solubility of α-mangostin causes limitations in its development in clinical purpose. To increase the solubility of a compound, a method currently being developed is to make drug inclusion complexes using cyclodextrins. This research aimed to use in silico techniques namely molecular docking study and molecular dynamics simulation to explore the molecular mechanism and stability of the encapsulation of α-mangostin using cyclodextrins. Two types of cyclodextrins were used including β-cyclodextrin and 2-hydroxypropyl-β-cyclodextrin docked against α-mangostin. From the molecular docking results, it shows that the α-mangostin complex with 2-hydroxypropyl-β-cyclodextrin provides the lowest binding energy value of -7.99 Kcal/mol compared to β-cyclodextrin value of -6.14 Kcal/mol. The α-mangostin complex with 2-hydroxypropyl-β-cyclodextrin also showed good stability based on molecular dynamics simulation during 100 ns. From molecular motion, RDF, Rg, SASA, density, total energy analyzes, this complex shows increased solubility in water and provided good stability. This indicates that the encapsulation of α-mangostin with 2-hydroxypropyl-β-cyclodextrin can increase the solubility of the α-mangostin.Communicated by Ramaswamy H. Sarma.

Synthesis, Characterization, Antibacterial, Antifungal and Anticorrosion Activities of 1,2,4-Triazolo[1,5-a]quinazolinone

The synthesis of 5,6,7,8-tetrahydro-[1,2,4]triazolo[5,1-b]quinazolin-9(4H)-one (THTQ), a potentially biologically active compound, was pursued, and its structure was determined through a sequence of spectral analysis, including ¹H-NMR, ¹³C-NMR, IR, and HRMS. Four bacterial and four fungal strains were evaluated for their susceptibility to the antibacterial and antifungal properties of the THTQ compound using the well diffusion method. The impact of THTQ on the corrosion of mild steel in a 1 M HCl solution was evaluated using various methods such as weight loss, potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) analysis. The study revealed that the effectiveness of THTQ as an inhibitor increased with the concentration but decreased with temperature. The PDP analysis suggested that THTQ acted as a mixed-type inhibitor, whereas the EIS data showed that it created a protective layer on the steel surface. This protective layer occurs due to the adsorption behavior of THTQ following Langmuir's adsorption isotherm. The inhibition potential of THTQ is also predicted theoretically using DFT at B3LYP and Monte Carlo simulation.

Insight into the corrosion mitigation performance of three novel benzimidazole derivatives of amino acids for carbon steel (X56) in 1 M HCl solution

Three new organic molecules having a benzimidazole base were synthesized and used for the protection of carbon steel (X56) against corrosion in 1.00 M HCl solution. The protection against corrosion was assessed by electrochemical frequency modulation (EFM), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP). In addition, the electronic and molecular structure of the synthesized molecules were computationally investigated and correlated to corrosion inhibition. Global reactivity descriptors, molecular orbitals (FMO and NBO) and local reactivity descriptors (molecular electrostatic potential map and Fukui functions) were discussed. The results showed a maximum protective efficiency range between 95% and 98% indicating high corrosion inhibition. Moreover, all molecules were able to combat the cathodic as well as anodic reaction simultaneously, revealing a mixed-type resistance. SEM and EDX verified effective adhering film formation to the metal surface. In accordance, the theoretical calculations showed effective electron reallocation from the organic film to the X56 c-steel surface. Furthermore, the adsorption annealing calculations revealed that structural layers of these molecules hold parallel and close to the metal surface with adsorption energy from 249.383 to 380.794 kcal mol^-1, showing strong inhibitor-metal contact.

Ethyl ester/acyl hydrazide-based aromatic sulfonamides: facile synthesis, structural characterization, electrochemical measurements and theoretical studies as effective corrosion inhibitors for mild steel in 1.0 M HCl

In this research paper, aromatic sulfonamide-derived ethyl ester (p-TSAE) and its acyl hydrazide (p-TSAH) were directly synthesized, characterized, and employed for the first time as prospective anticorrosive agents to protect mild steel in 1.0 M HCl conditions. The corrosion efficiency was probed by electrochemical methods including polarization, impedance, and frequency modulation measurements. Optimal efficiencies of 94% and 92% were detected for the hydrazide and ester, respectively, revealing excellent corrosion inhibition. Moreover, both the hydrazide and ester molecules combat the cathodic and anodic reactions correspondingly in a mixed-type manner. The electron transfer (ET) at the inhibitor/metal interface was evaluated using DFT at the B3LYP/6-31g(d,p) level. Natural bond orbital analysis (NBO) and frontier molecular orbital analysis (FMO) calculations showed superior capabilities of the synthesized inhibitors to easily reallocate charge into the metal surface. However, the hydrazide molecules showed slightly better inhibition efficiency than the ester due to the strong interaction between the lone pairs of the nitrogen atoms and the d-orbitals of the metal. The chemical hardness of the hydrazide and ester are 2.507 and 2.511 eV, respectively, in good accordance with the recorded electrochemical inhibition efficiencies for both molecules. Good and straightforward correlations between the experiments and calculations are obtained.

Theoretical Study and Adsorption Behavior of Urea on Mild Steel in Automotive Gas Oil (AGO) Medium

The continuous search for eco-friendly corrosion inhibitors due to differences in corrosive media remains an important point in corrosion control. The experimental studies on the corrosion inhibition of urea on mild steel in automotive gas oil (AGO) was conducted using gasometric techniques and scanning electron microscope (SEM). The theoretical approach on the density functional theory (DFT) on the urea molecule was carried out using Gaussian 09 software. The adsorption behavior of urea molecules on the surface of the mild steel was analyzed using Frumkin and Flory-Huggins adsorption isotherms models and Gibb’s free energy, respectively. The result of the experimental study shows a poor corrosion inhibitory effect of urea on mild steel in automobile gas oil (AGO) medium as the inhibition efficiency decreased from 69.30% in week 1 to 12% in week 11 at 200 ppm of inhibitor. The adsorption of urea on the mild steel surface obeys Frumkin’s adsorption isotherm model. Gibb’s free energy of adsorption of urea molecules onto mild steel surface revealed a physisorption mechanism. SEM results showed the non-inhibitive nature of urea on the studied mild steel. Quantum chemical parameters such as HOMO, LUMO, electron affinity, electronegativity, and the fraction of electrons transferred to the metal surface were calculated and interpreted to compare the experimental and theoretical results. The theoretical findings in the current investigation were not in agreement with the experimental result, thereby creating a need for further study using the electrochemical method.

In Silico Approaches for Some Sulfa Drugs as Eco-Friendly Corrosion Inhibitors of Iron in Aqueous Medium

This paper addresses the prediction of the adsorption behavior as well as the inhibition capacity of non-toxic sulfonamide-based molecules, also called sulfa drugs, on the surface of mild steel. The study of the electronic structure was investigated through quantum chemical calculations using the density functional theory method (DFT) and the direct interaction of inhibitors with the iron (Fe) metal surface was predicted using the multiple probability Monte Carlo simulations (MC). Then, the examination of the solubility and the environmental toxicity was confirmed using a chemical database modeling environment website. It was shown that the presence of substituents containing heteroatoms able to release electrons consequently increased the electron density in the lowest unoccupied and highest occupied molecular orbitals (LUMO and HOMO), which allowed a good interaction between the inhibitors and the steel surface. The high values of EHOMO imply an ability to donate electrons while the low values of ELUMO are related to the ability to accept electrons thus allowing good adsorption of the inhibitor molecules on the steel surface. Molecular dynamics simulations revealed that all sulfonamide molecules adsorb flat on the metal surface conforming to the highly protective Fe (1 1 0) surface. The results obtained from the quantum chemistry and molecular dynamics studies are consistent and reveal that the order of effectiveness of the sulfonamide compounds is P7 > P5 > P6 > P1 > P2 > P3 > P4.

Thiophene derivatives as corrosion inhibitors for 2024-T3 aluminum alloy in hydrochloric acid medium

Thiophene derivatives, namely (E)-thiophene-2-carbaldehyde oxime (OXM) and (E)-5-(thiophen-2-yl)-1H-tetrazole (TET), were synthesized and characterized via¹H and ¹³C NMR. Furthermore, their inhibitory property for AA2024-T3 in 1 M HCl solution was investigated via electrochemical impedance spectroscopy and potentiodynamic polarization at 293 K, together with DFT/B3LYP-based calculations. Numerous global and local descriptors of reactivity such as EHOMO, ELUMO, energy gap, electronegativity (χ), hardness (η), and frontier molecular orbital repartitions were investigated to describe the reactivity of each molecule. Alternatively, Monte Carlo simulations were performed under the solvation condition on the Al (111) surface to understand the adsorption behavior of the as-studied inhibitors deeply. The inhibition efficiency increased with an increase in the inhibitor concentration, achieving maximum values of 94.0% and 96% at 10⁻³ M, respectively. The polarization curves showed that the examined compounds act as mixed-type inhibitors. In addition, the adsorption of these compounds obeyed the Al Awady, Flory-Huggins and Temkin isotherms. The surface characterization analysis via SEM/EDX confirmed the presence of a barrier layer covering the aluminum surface. The experimental inhibition efficiencies were correlated with global descriptors, which confirmed that this theoretical study is useful for the protection of aluminum alloy metal in an acidic medium.

Thiophene derivatives: thiophene-2-carbaldehyde oxime (OXM) and 5-(thiophen-2-yl)-1H-tetrazole (TET), were synthesized and characterized. Furthermore, their inhibitory property for AA2024-T3 in 1 M HCl solution was investigated via electrochemical and with theoretical study.

Quantum Chemical Studies and Electrochemical Investigations of Polymerized Brilliant Blue-Modified Carbon Paste Electrode for In Vitro Sensing of Pharmaceutical Samples

To develop an electrochemical sensor for electroactive molecules, the choice and prediction of redox reactive sites of the modifier play a critical role in establishing the sensing mediating mechanism. Therefore, to understand the mediating mechanism of the modifier, we used advanced density functional theory (DFT)-based quantum chemical modeling. A carbon paste electrode (CPE) was modified with electropolymerization of brilliant blue, later employed for the detection of paracetamol (PA) and folic acid (FA). PA is an analgesic, anti-inflammatory and antipyretic prescription commonly used in medical fields, and overdose or prolonged use may harm the liver and kidney. The deficiency of FA associated with neural tube defects (NTDs) and therefore the quantification of FA are very essential to prevent the problems associated with congenital deformities of the spinal column, skull and brain of the fetus in pregnant women. Hence, an electrochemical sensor based on a polymerized brilliant blue-modified carbon paste working electrode (BRB/CPE) was fabricated for the quantification of PA and FA in physiological pH. The real analytical applicability of the proposed sensor was judged by employing it in analysis of a pharmaceutical sample, and good recovery results were obtained. The potential excipients do not have a significant contribution to the electro-oxidation of PA at BRB/CPE, which makes it a promising electrochemical sensing platform. The real analytical applicability of the proposed method is valid for pharmaceutical analysis in the presence of possible excipients. The prediction of redox reactive sites of the modifier by advanced quantum chemical modeling-based DFT may lay a new foundation for researchers to establish the modifier–analyte interaction mechanisms.

Synthesis, Molecular Docking, MEP and SAR Analysis, ADME-Tox Predictions, and Antimicrobial Evaluation of Novel Mono- and Tetra-Alkylated Pyrazole and Triazole Ligands

Newly synthesized compounds of N-alkylated heterocyclic compounds were prepared by condensation of amine with alcohol which undergoes a reaction of SN2. These newly synthesized derivatives were characterized by spectral analysis. The objective is to prepare new potent nontoxic antimicrobial agents which are easy to synthesize and could be scaled up in pharmaceutical industries. Thirteen new heterocyclic compounds containing a pyrazole moiety were synthesized with good yields (29.79 to 99.6%) and were characterized by FTIR, 1H NMR, 13C NMR, and CG-MS techniques. The compounds were divided into two series—monoalkylated compounds (1–11) and tetra-alkylated compounds (12 and 13)—and then evaluated for their in vitro antifungal and antibacterial activities against several fungal and bacterial strains. None of the monoalkylated compounds had antibacterial or antifungal activity. However, the two tetra-alkylated pyrazole ligands displayed strong antibacterial potential. Moreover, compound 12 was more potent against all tested bacterial strains than compound 13. Interestingly, compounds 12 and 13 acted as weak antifungal agents against Saccharomyces cerevisiae. ADME-Tox studies suggested that compounds 12 and 13 exhibit better toxicity profiles than the commercial antibiotic streptomycin. MEP studies suggested that compounds 12 and 13 have the same charge locations but differ in their values which are due to the condensed geometry of compound 13 that make it more polarizable than compound 12. Of particular interest, these different MEPs were evident in ligand protein docking, suggesting that compound 12 has better affinity with MGL enzyme than compound 13. All these findings suggested that these novel compounds represent promising antibacterial lead compounds.

Novel triazole derivatives as ecological corrosion inhibitors for mild steel in 1.0 M HCl: experimental & theoretical approach

The present paper illustrates the investigation of two novel ecological triazole derivative corrosion inhibitors, namely ethyl 2-(4-phenyl-1H-1,2,3-triazol-1-yl) acetate [Tria-CO₂Et], and 2-(4-phenyl-1H-1,2,3-triazol-1-yl) acetohydrazide [Tria-CONHNH₂].