Quantum Chemical Assessment Research Articles

Quantum chemical assessment of benzimidazole derivatives as corrosion inhibitors

BackgroundThe majority of well-known inhibitors are organic compounds containing multiple bonds and heteroatoms, such as O, N or S, which allow adsorption onto the metal surface. These compounds can adsorb onto the metal surface and block active surface sites, reducing the rate of corrosion.ResultsA comparative theoretical study of three benzimidazole isomers, benzimidazole (BI), 2-methylbenzimidazole (2-CH3-BI), and 2-mercaptobenzimidazole (2-SH-BI), as corrosion inhibitors was performed using density functional theory (DFT) with the B3LYP functional basis set.ConclusionsNitro and amino groups were selected for investigation as substituents of the three corrosion inhibitors. Nitration of the corrosion inhibitor molecules led to a decrease in inhibition efficiency, while reduction of the nitro group led to an increase in inhibition efficiency. These aminobenzimidazole isomers represent a significant improvement in the inhibition efficiency of corrosion inhibitor molecules.

Electrochemical and quantum chemical assessment of two organic compounds from pyridine derivatives as corrosion inhibitors for mild steel in HCl solution under stagnant condition and hydrodynamic flow

In this study, the inhibitive performance of two pyridine derivatives as corrosion inhibitors for mild steel was examined under stagnant condition and hydrodynamic flow in HCl solution at 25°C. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques were employed. To explore the inhibitors adsorption mechanism, Langmuir isotherm and quantum chemical studies were used. The results of electrochemical measurements show that the inhibitor concentration has a positive effect on its efficiency while for hydrodynamic condition, it is vice versa. Corrosion attack morphologies were observed at stagnant and hydrodynamic conditions to verify qualitatively the results obtained by electrochemical methods.

Quantum-chemical assessment of the flotation activity of RNKh-3010 reagent

The flotation activity of RNKh-3010 reagent with respect to coal is assessed on the basis of quantum-chemical characteristics. Calculations by a semiempirical method indicate that the compounds in the reagent are strictly nucleophilic and may compete with water molecules for electrophilic adsorption centers of the coal surface. Flotation reagents may be selected on the basis of their quantum-chemical characteristics.

Single-Event MicroKinetics of Aromatics Hydrogenation on Pt/H-ZSM22

A fundamental Single-Event MicroKinetic (SEMK) model for the hydrogenation of aromatic components on a Pt catalyst has been developed. It is based on the Horiuti-Polanyi mechanism considering atomic hydrogen addition steps to the (partially hydrogenated) aromatic species on the catalyst surface. The reaction network used accounts for the position at which the hydrogen atoms are added to the ring. In accordance with a quantum chemical assessment of the reaction pathway it was assumed that the kinetic parameters only depend on the saturation degree of the nearest neighbor carbon atoms and the branching degree of the carbon atom involved in the hydrogen atom addition. Six reactions families, of which three occur in the reaction network for benzene, are considered. The total number of 18 model parameters was reduced to 7 by calculation of the pre-exponential factors and by accounting for thermodynamic constraints. Experimental benzene hydrogenation data measured at temperatures in the range from 423 to 498 K,...

Quantum chemical assessment of the binding energy of CuO+

We present a detailed theoretical investigation on the dissociation energy of CuO(+), carried out by means of coupled cluster theory, the multireference averaged coupled pair functional (MR-ACPF) approach, diffusion quantum Monte Carlo (DMC), and density functional theory (DFT). At the respective extrapolated basis set limits, most post-Hartree-Fock approaches agree within a narrow error margin on a D(e) value of 26.0 kcal mol(-1) [coupled-cluster singles and doubles level augmented by perturbative triples corrections, CCSD(T)], 25.8 kcal mol(-1) (CCSDTQ via the high accuracy extrapolated ab initio thermochemistry protocol), and 25.6 kcal mol(-1) (DMC), which is encouraging in view of the disaccording data published thus far. The configuration-interaction based MR-ACPF expansion, which includes single and double excitations only, gives a slightly lower value of 24.1 kcal mol(-1), indicating that large basis sets and triple excitation patterns are necessary ingredients for a quantitative assessment. Our best estimate for D(0) at the CCSD(T) level is 25.3 kcal mol(-1), which is somewhat lower than the latest experimental value (D(0) = 31.1 ± 2.8 kcal mol(-1)[semicolon] reported by the Armentrout group) [Int. J. Mass Spectrom. 182/183, 99 (1999)]. These highly correlated methods are, however, computationally very demanding, and the results are therefore supplemented with those of more affordable DFT calculations. If used in combination with moderately-sized basis sets, the M05 and M06 hybrid functionals turn out to be promising candidates for studies on much larger systems containing a [CuO](+) core.

Viability of pyrite pulled metabolism in the ‘iron-sulfur world’ theory: Quantum chemical assessment

The viability of pyrite-pulled metabolism in the ‘iron-sulfur world’ theory was assessed using a simple model of iron–nickel sulfide (Fe–Ni–S) surface and data obtained from quantum chemical calculations. We have investigated how the individual reactions in the carbon fixation cycle (carboxylic acids formation) on an Fe–Ni–S surface could have operated to produce carboxylic acids from carbon oxide and water. The proposed model cycle reveals how the individual reactions might have functioned and provides the thermodynamics of each step of the proposed pathway. The feasibility of individual reactions, as well the whole cycle was considered. The reaction of acetic acid production from CH 3SH and CO on an Fe–Ni sulfide surface was revealed to be endergonic with a few partial steps having positive Gibbs free energy. On the other hand, the pyrite formation was found to be slightly exergonic. The significance of the catalytic activity of transition metal sulfides in generation of acetic acid was shown. The Gibbs free energy values indicate that the acetic acid synthesis is unfavorable to proceed on the studied Fe–Ni–S model under simulated conditions. The importance of these results in terms of a primordial chemistry on iron–nickel sulfide surfaces is discussed.

Quantum chemical assessment of the structure of an oxygen radical adsorbed on titania and detected by ESR spectroscopy

In order to clarify the nature of a radical previously detected by ESR on TiO 2 surfaces after UV irradiation under O 2, CNDO and INDO calculations are per formed on O −z 3 and O −z 3 (MX 3) 2 models, where z=1 or 3, and MX 3 = SiF + 3 or Al(OH) − 3 accounts for the stabilizing surface cations. The results indicate that the shape and the symmetry predicted for the half-occupied orbital change when the effect of the solid surface is introduced via the MX 3 groups, so that the model with z=3, previously questioned on the basis of simpler calculations, becomes more favoured. The need to include the neighbouring groups in order to get a meaningful quantum-chemical simulation of such surface species is emphasized.

Quantum chemical assessment of the possibility of soliton switching.

Bond deformation in the photon-excited state of simplified model systems designed for soliton switching was examined in a quantum chemical manner. It has been concluded that occurrence of the structural change indispensable to the switching function is doubtful.