Insight into Anticorrosion Mechanism of Ampicillin on Mild Steel in Acidic Environment: A Combined Experimental and Theoretical Approach

The corrosion inhibition of mild carbon steels in an acidic environment by using ampicillin (AMP) has been evaluated based on experimental and quantum chemistry techniques. The experimental results indicate that the inhibition efficiency goes up at higher AMP concentration. The highest inhibition efficiency reaches 84.9% for polarization measurement and 90.1% for electrochemical impedance spectroscopy with the inhibitor of concentration 100 ppm at 298 K. The surface characteristics (SEM) also reconfirm the steel corrosion inhibition ability of AMP. Some important chemical factors such as EHOMO (highest occupied molecular orbital energy), ELUMO (lowest unoccupied molecular orbital energy), ΔEL−H (energy gap), and Fukui functions were calculated based on the optimized configuration of AMP at the theoretical level of B3LYP/6-31+G(d,p). Moreover, Monte Carlo and molecular dynamics simulations were used to analyze the absorption behavior of inhibitor on the surface of Fe(110), which supplies the mechanism of inhibition corrosion processes. The obtained results showed that AMP is considered to be a potential corrosion inhibitor for mild steel in 1M HCl medium. Moreover, the protonated state of AMP plays an important role in the protection of Fe surface against the corrosive process.

Synthesis, spectroscopic investigation, crystal structure analysis, quantum chemical study, biological activity and molecular docking of three isatin derivatives

Three isatin derivatives, namely, 1-allyl-3-hydroxy-3-(6-oxocyclohex-1-en-1-yl)indolin-2-one, C17H17NO3, 1-ethyl-3-hydroxy-3-(6-oxocyclohex-1-en-1-yl)indolin-2-one, C16H17NO3, and 5-bromo-3-hydroxy-1-methyl-3-(6-oxocyclohex-1-en-1-yl)indolin-2-one, C15H14BrNO3, were synthesized, crystallized by the slow-evaporation technique, characterized by 1H and 13C NMR spectroscopy, and analysed by the single-crystal X-ray diffraction (XRD) method. Quantum chemical parameters, such as the energy of the highest occupied molecular orbital, energy of the lowest unoccupied molecular orbital, energy gap, electronic energy, ionization potential, chemical potential, global hardness, global softness and electrophilicity index, were calculated. The druglikeness and bioactivity scores of the compounds were calculated. The activities of these isatin derivatives against bacterial strains, such as Eschericia coli, Proteus vulgaris, Shigella flexneri, Staphylococcus aureus and Micrococcus luteus, and the fungal strain Aspergillus niger, were determined using the well-diffusion assay method. Molecular docking studies were carried out to predict the binding mode of the isatin compounds with the penicillin binding protein enzyme and to identify the interactions between the enzyme and the ligands under study.

Computational Methods and Molecular Modelling for Some Predicted Tautomers of Pyrimidine compounds

Introduction: Several molecular modelling techniques and quantum chemical methods have been performed to correlate the chemical structures of the compounds with their physical molecular properties. Methods: Using theoretical parameters help to characterize the molecular structure of the investigated ligands and to study their equlibria mechanism. Molecular modelling data such as the bond length, bond order, bond angles and dihedral angles values were estimated for some pyrimidine compounds, where the data suggested the presence of tautomerism and a dynamic equilibria are deduced between all the detected tautomers in the solid state. Results: Four main tautomers are predicted for barbital and thiobarbituric acid while three tautomers are for thiouracil. Quantum chemical parameters such as the highest occupied molecular orbital energy (EHOMO), the lowest unoccupied molecular orbital energy (ELUMO), energy gap (ΔE), dipole moment (µ ), sum of the total negative charge (STNC), electronegativity (Χ), chemical potential (Pi), global hardness (η) and softness (σ ) were calculated.

Theoretical Evaluation of the Corrosion Inhibition Performance of an Organic Heterocyclic Compound

The corrosion inhibition performance of a corrosion inhibitor on mild steel in phosphoric acid, namely 5-chloro-1-(2-(dimethylamino) ethyl) indoline-2,3-dione (TZCDI), was theoretically evaluated using density functional theory (DFT) at the B3LYP/6-31G+(d,p) level for all atoms by Gaussian 09W program. The quantum chemical properties, such as highest occupied molecular orbital energy (EHOMO), lowest unoccupied molecular orbital energy (ELUMO) energy gap (∆Egap), dipole moment (μ), total hardness (η), and electronegativity (χ), were studied, and these descriptors were discussed in connection to the experimental inhibitory efficiency. The local reactivity was analyzed through the Fukui function in order to compare the possible sites for nucleophilic and electrophilic attacks. Accordingly, all data obtained using various theoretical calculation techniques were consistent with experiments.

Theoretical Study of the Structure and Property of Ionic Liquids as Corrosion Inhibitor

Three sets of ionic liquids such as 1-alkyl-3-methylimidazole chloride [Cnmim]Cl, 1-alkyl-3-methylimidazolium acetate [Cnmim]Ac and 1-octyl-3-methylimidazole salt [Omim]Y (n = 2, 4, 6, 8, and Y = Cl, BF4, HSO4, Ac and TFO) were used as corrosion inhibitor medium for corrosion protection of carbon steel. Electronic structures and reactivity of these ionic liquids, surface energy and electronic structures of the iron surface were systematically analyzed by density functional theory. By increasing the alkyl chain length of the [Cnmim]Cl and [Cnmim]Ac systems, the lowest unoccupied molecular orbital energy (ELUMO), the highest occupied molecular orbital energy (EHOMO), the softness (S) and polarizability (α) increased gradually, whereas electronegativity (χ), energy gap (ΔE), hardness (η), dipole moment (μ)and electrophilic index (ω) gradually decreased. For the [Omim]Y system, the structure parameters of ionic liquids are quite different, and only the polarizability (α) decreases gradually by increasing the length of the alkyl chain. The results show that inhibition is mainly [Cnmim]+ cations of the [Cnmim]Cl system, and the order of inhibition efficiency follows as [C2mim]Cl < [C4mim]Cl < [C6mim]Cl < [C8mim]Cl. Both [Cnmim]+ cations and the Ac− anion have inhibition effect for the [Xmim]Ac system, and the order of inhibition efficiency is [C8mim]Ac > [C6mim]Ac > [C4mim]Ac > [C2mim]Ac. For the [Omim]Y system, [Xmim]+ cations and anions (BF4−, HSO4−, Ac−, TfO−) have inhibition effect, and the order of inhibition efficiency is [Omim]TfO > [Omim]Ac > [Omim]HSO4 > [Omim]BF4 > [Omim]Cl.

Dielectric, Electrical Conductivity Behavior and Molecular Modeling of Some Pyrimidine and Purine Compounds

The dielectric and electrical conductivity measurements for biologically active nucleic acid compounds reveal semiconducting properties and small relaxation times. On the basis of electronic transition within molecules, two pathways for the conduction of electricity may be expected. The first conducting process occurring in the lower temperature region is attributed to n→π* transitions which require less energy to be performed. In the upper temperature region, conduction could be attributed to π→π* transitions which need more energy to participate in electronic conduction. The observed increment of conduction in the upper temperature region may be attributed to interactions between n→π* and π→π* transitions. Quantum chemical parameters such as the highest occupied molecular orbital energy (EHOMO) and the lowest unoccupied molecular orbital energy (ELUMO) were given using molecular modeling. Energy gap (ΔE) and parameters which give information about the reactive chemical behavior of compounds such as electronegativity (χ), chemical potential (µ), global hardness (η), softness (σ) and electrophilicity index (ω) were calculated.

3(4)-Amino-4(3)-nitro-1,2,5-oxadiazole-2-oxides and their Ring-opened Isomers-A DFT Treatment

Amino and nitro substituted 1,2,5-oxadiazole-2-oxide isomers and their ring-opened nitroso forms have been subjected to density functional treatment at the level of B3LYP/6-311++G(d,p). The transition states for the ring opening processes are obtained and the corresponding activation energies have been calculated. Also, 1,3- and 1,5-proton tautomerism yielding imine, oxime and aci forms are investigated. For all the structures, the stabilities, the HOMO, LUMO energies and the interfrontier molecular orbital energy gaps are obtained and the effects of substituents (NH2 and NO2) are discussed.