The inhibitive action of 2-mercaptobenzothiazole on the porosity of corrosion film formed on aluminum and aluminum-titanium alloys in hydrochloric acid solution.

2-Mercaptobenzothiazole (2-MBT) in a solution of 0.5 M HCl is an effective corrosion inhibitor for aluminum and aluminum-titanium alloys. Tafel polarization and electrochemical impedance spectroscopy (EIS) were employed to assess this heterocyclic compound's anticorrosive potential and complementary by scanning electron microscope (SEM) and calculating porosity percentage in the absence and presence of various inhibitor concentrations. Inhibition efficiency (IE%) was strongly related to concentration (10-6-10-3 M). Temperature's effect on corrosion behavior was investigated. The data exhibited that the IE% decreases as the temperature increases. An increase in activation energy (Ea) with increasing the inhibitor concentration and the decrease in the IE% value of the mentioned compound with raising the temperature indicates that the inhibitor molecules are adsorbed physically on the surface. Thermodynamic activation parameters for Al and Al-Ti alloy dissolution in both 0.5 M HCl and the inhibited solution were calculated and discussed. According to Langmuir's adsorption isotherm, the inhibitor molecules were adsorbed. The evaluated standard values of the enthalpy ([Formula: see text], entropy ([Formula: see text] and free energy changes ([Formula: see text] showed that [Formula: see text] and [Formula: see text] are negative, while [Formula: see text] was positive. The formation of a protective layer adsorbed on the surfaces of the substrates was confirmed with the surface analysis (SEM). The porosity percentage is significantly reduced in the inhibitor presence and gradually decreased with increasing concentration. Furthermore, the density functional theory (DFT) and Monte Carlo (MC) simulations were employed to explain the variance in protecting the Al surface from corrosion. Interestingly, the theoretical findings align with their experimental counterparts. The planarity of 2-MBT and the presence of heteroatoms are the playmakers in the adsorption process.

Pyridinium-Inspired Organocatalysts for Carbon Dioxide Fixation: A Density Functional Theory Inspection.

The current project aims to apply the virtues of minimalism to examine the catalytic ability of commercially organic compounds of small chemical structures to catalyze the coupling reaction between carbon dioxide and propylene oxide (PO) under mild conditions. The proposed catalysts are pyridinium iodide (A), 2-hydroxypyridinium iodide (B), and piperidinium iodide (C), where their structure is based on cooperative acidic and nucleophilic motifs. The quantum chemistry model, M062X-D3/def2-TZVP//M062X-D3/def2-SVPP, was used to understand the reaction mechanism and the catalytic performance. Since the coupling reaction was performed under excess PO, we proposed that PO serves as a reactant and solvent. Therefore, calculations were performed in gas and liquid phases for comparison. The findings indicated that the rate-determining step depends on the chemical structure of the catalyst and whether the phase is a gas or liquid phase. In general, modeling in the liquid phase produces potential energy surfaces of lower energy barriers. The noncovalent interactions reflect the role of hydrogen bonding in controlling the kinetic behavior of the coupling reaction. Based on the finding, catalyst A is the best candidate for transforming CO2 into cyclic carbonates.

Synthesis of Cyano-Benzylidene Xanthene Synthons Using a Diprotic Brønsted Acid Catalyst, and Their Application as Efficient Inhibitors of Aluminum Corrosion in Alkaline Solutions.

Novel cyano-benzylidene xanthene derivatives were synthesized using one-pot and condensation reactions. A diprotic Brønsted acid (i.e., oxalic acid) was used as an effective catalyst for the promotion of the synthesis process of the new starting xanthene-aldehyde compound. Different xanthene concentrations (ca. 0.1-2.0 mM) were applied as corrosion inhibitors to control the alkaline uniform corrosion of aluminum. Measurements were conducted in 1.0 M NaOH solution using Tafel extrapolation and linear polarization resistance (LPR) methods. The investigated xanthenes acted as mixed-type inhibitors that primarily affect the anodic process. Their inhibition efficiency values were enhanced with inhibitor concentration, and varied according to their chemical structures. At a concentration of 2.0 mM, the best-performing studied xanthene derivative recorded maximum inhibition efficiency values of 98.9% (calculated via the Tafel extrapolation method) and 98.4% (estimated via the LPR method). Scanning electron microscopy (SEM) was used to examine the morphology of the corroded and inhibited aluminum surfaces, revealing strong inhibitory action of each studied compound. High-resolution X-ray photoelectron spectroscopy (XPS) profiles validated the inhibitor compounds' adsorption on the Al surface. Density functional theory (DFT) and Monte Carlo simulations were applied to investigate the distinction of the anticorrosive behavior among the studied xanthenes toward the Al (111) surface. The non-planarity of xanthenes and the presence of the nitrile group were the key players in the adsorption process. A match between the experimental and theoretical findings was evidenced.

The anti-corrosive behavior of benzo-fused N-heterocycles: an in silico study toward developing organic corrosion inhibitors.

The work provides a computational protocol to predict the anti-corrosive performance of organic molecules through three successive phases of calculations; electron propagator theory (EPT), Monte Carlo (MC) simulations, and the density functional based tight-binding (DFTB) method. The protocol was applied to investigate the influence of two structural factors on the anti-corrosive performance of benzo fused-N-heterocycles (BFNHs) against the Fe(110) surface in an acidic medium; positional isomerism and the gradual insertion of nitrogen atoms in the heterocycle ring. The choice of BFNHs is attributed to their anti-corrosion activity and their use as building blocks in the molecular structure of many organic inhibitors. The findings indicate that EPT is a safe method for calculating the quantum chemical descriptors of the isolated molecules. Besides, the current work recommends using MC simulations and the DFTB method to describe the physical and chemical adsorption, respectively. Unexpected results were observed, as the gradual insertion of nitrogen atoms is not a specific factor for improving the inhibition efficiency of BFNHs. The findings were crystallized in equations linking the physical and chemical adsorption energies with the quantum chemical descriptors with a correlation exceeding 0.75. Besides, the peri steric hindrance plays an influential role in chemical adsorption. Intriguingly, the continuous introduction of nitrogen atoms does not increase the efficiency of the inhibitor along the way. For example, phthalazine exhibited better efficiency than benzotetrazine. In light of the above, the present protocol helps understand the anti-corrosive behavior of organic inhibitors and provides a feasible method to develop novel corrosion inhibitors.

A DFT-design of single component bifunctional organocatalysts for the carbon dioxide/propylene oxide coupling reaction.

The aim of this work is to develop single-component bifunctional organic catalysts capable of effective coupling reactions between CO2 and propylene epoxide (PO) under mild conditions using density functional theory (DFT) calculations. The dual functionalities of the target catalysts come from their inclusion of a hydroxyl-containing electrophile and the nucleophilicity of iodide ion. In this respect, a series of hydroxyl-functionalized quaternary onium-based ionic liquids were studied using M062X-D3/def2-TZVP//M062X-D3/def2-SVPP model chemistry. The design of catalysts was based on tailoring two structural factors; the first one is the onium center of pnictogens (N, P, As, Sb and Bi), and the second one is the number of hydrogen bond donor groups (n = 1-3). The proposed catalysts were examined by investigation of their catalytic mechanisms to afford the cyclic carbonate. Additionally, the highest active transition state, along with the potential energy difference, was examined using non-covalent interaction (NCI) analysis. Also, the activation strain model (ASM) was used to explain the kinetic behavior of PO activation. The findings showed that the ring-opening step of PO is always the critical step of the reaction. Among the suggested catalysts, the results indicated that the dihydroxyl ammonium-based catalyst (2OH-NI) is a good choice for this catalysis under mild and solvent-free conditions.

Diaryl Sulfide Derivatives as Potential Iron Corrosion Inhibitors: A Computational Study.

The present work aimed to assess six diaryl sulfide derivatives as potential corrosion inhibitors. These derivatives were compared with dapsone (4,4'-diaminodiphenyl sulfone), a common leprosy antibiotic that has been shown to resist the corrosion of mild steel in acidic media with a corrosion efficiency exceeding 90%. Since all the studied compounds possess a common molecular backbone (diphenyl sulfide), dapsone was taken as the reference compound to evaluate the efficiency of the remainder. In this respect, two structural factors were examined, namely, (i) the effect of replacement of the S-atom of diaryl sulfide by SO or SO2 group, (ii) the effect of the introduction of an electron-withdrawing or an electron-donating group in the aryl moiety. Two computational chemical approaches were used to achieve the objectives: the density functional theory (DFT) and the Monto Carlo (MC) simulation. First, B3LYP/6-311+G(d,p) model chemistry was employed to calculate quantum chemical descriptors of the studied molecules and their geometric and electronic structures. Additionally, the mode of adsorption of the tested molecules was investigated using MC simulation. In general, the adsorption process was favorable for molecules with a lower dipole moment. Based on the adsorption energy results, five diaryl sulfide derivatives are expected to act as better corrosion inhibitors than dapsone.

Intramolecular electron transfer of light harvesting perylene-pyrene supramolecular conjugate.

Electronic interactions between the cationic N,N'-bis(2(trimethylammonium iodide) ethylene)perylene-3,4,9,10-tetracarboxyldiimide (TAIPDI) with two electron donors, namely, pyrene (Py) and 1-pyrenesulfonic acid sodium salt (PySA), have been investigated. The spectroscopic studies showed the formation of the supramolecular conjugate between TAIPDI and PySA via ionic interaction, but not with Py. Density functional theory (DFT) combined with a natural energy decomposition analysis (NEDA) technique showed an S-like structure of the supramolecular conjugate TAIPDI-PySA via an ionic interaction. The formation constant of the TAIPDI-PySA supramolecular conjugate was determined to be 3.0 × 104 M-1, suggesting a fairly stable complex formation. The excited state events were monitored by both steady state and time-resolved emission techniques. Upon excitation, the quenching pathways via the singlet-excited states of TAIPDI and PySA involved the intramolecular electron transfer from the electron donating PySA to the electron accepting TAIPDI with a rate constant of 1.10 × 1011 s-1 and a quantum yield of 0.99. The thermodynamic parameters of the supramolecular TAIPDI-PySA conjugate have been determined using the stopped-flow technique.

Synthesis and photophysical properties of the 2-(3-(2-Alkyl-6,8-diaryl-4-oxo-1,2,3,4-tetrahydroquinazolin-2-yl)propyl)-6,8-diarylquinazolin-4(3H)-ones.

Iodine-catalyzed condensation of 2-amino-3,5-dibromobenzamide with cyclohexane-1,3-dione derivatives in refluxing toluene afforded the corresponding bisquinazolinones. Suzuki-Miyaura cross-coupling of the latter with arylboronic acids afforded tetraarylbisquinazolinones. The electronic absorption and emission properties of these tetraarylbisquinazolinones were measured in dimethylsulfoxide (DMSO) and acetic acid by means of UV-Vis and fluorescence spectroscopic techniques in conjunction with quantum chemical methods to understand the influence of substituents on intramolecular charge transfer (ICT).

Synthesis and photophysical property studies of the 2,6,8-triaryl-4-(phenylethynyl)quinazolines.

The 2-aryl-6,8-dibromo-4-chloroquinazolines derived from the 2-aryl-6,8-dibromoquinazolin-4(3H)-ones were subjected to the Sonogashira cross-coupling with terminal acetylenes at room temperature to afford novel 2-aryl-6,8-dibromo-4-(alkynyl)quinazoline derivatives. Further transformation of the 2-aryl-6,8-dibromo-4-(phenylethynyl)quinazolines via Suzuki-Miyaura cross-coupling with arylboronic acids occurred without selectivity to afford the corresponding 2,6,8-triaryl-4-(phenylethynyl)quinazolines. The absorption and emission properties of these polysubstituted quinazolines were also determined.

Aromatic ring size effects on the photophysics and photochemistry of styrylbenzothiazole.

The effect of ring size on the photophysics and photochemistry of styrylbenzothiazole has been investigated via systematic replacement of the phenyl ring of 1-phenyl-2-(2-benzothiazolyl)ethene with naphthyl and phenanthryl rings. Steady state absorption and fluorescence techniques have been employed to record the spectra in a variety of solvents, in conjunction with density functional theory (DFT) calculations, to probe absorption spectra and other properties of relevance to photo-excitation. Important experimental parameters were determined, such as fluorescence quantum yield and quantum yields of photochemical E-Z isomerisation. In addition, the computed potential energy surfaces of the ground and excited states were constructed using DFT/TD-DFT methods that showed that the photo-reaction is based on an adiabatic mechanism, in the sense that the reaction occurs via the excited-state potential energy surface. Based on the significant blue shift of the Z-isomer absorption maximum relative to that of the E-isomer, and the high percentage of Z-isomers in the photo-stationary state, these compounds may serve as potential promising candidates for optical data storage applications.

Comparative studies for evaluation of CO2 fixation in the cavity of the Rubisco enzyme using QM, QM/MM and linear-scaling DFT methods.

We evaluate the minimum energy configuration (MM) and binding free energy (QM/MM and QM) of CO2 to Rubisco, of fundamental importance to the carboxylation step of the reaction. Two structural motifs have been used to achieve this goal, one of which starts from the initial X-ray Protein Data Bank structure of Rubisco's active centre (671 atoms), and the other is a simplified, smaller model (77 atoms) which has been used most successfully, thus far, for study. The small model is subjected to quantum chemical density functional theory (DFT) studies, both in vacuo and using implicit solvation. The effects of the protein environment are also included by means of a hybrid quantum mechanical/molecular mechanical (QM/MM) approach, using PM6/AMBER and B3LYP/AMBER schemes. Finally, linear-scaling DFT methods have also been applied to evaluate energetic features of the large motif, and the result obtained for the binding free energy of the CO2 underlines the importance of the accurate modelling of the surrounding protein milieu using a full DFT description.

Diffusion and interactions of carbon dioxide and oxygen in the vicinity of the active site of Rubisco: molecular dynamics and quantum chemical studies.

Molecular dynamics (MD) at the molecular mechanical level and geometry optimisation at the quantum mechanical level have been performed to investigate the transport and fixation of oxygen and carbon dioxide in the cavity of ribulose-1,5-bisphosphate carboxylase/oxygenase, or Rubisco. Multiple MD simulations have been carried out to study the diffusive behaviour of O(2) and CO(2) molecules from the Mg(2+) cation in Rubisco at 298 K and 1 bar, being one step in the overall process of carboxylation/oxygenation in Rubisco. In addition to this work, in order to gain additional perspective on the role of chemical reaction rates and thermodynamics, oxygen, and carbon dioxide uptake mechanisms have also been investigated by the aid of quantum chemical calculations. The results indicate that the activation barrier for carboxylation is slightly lower than that of oxygenation. This agrees qualitatively with experimental findings, and rationalises the observed competition between both catalytic processes in nature. Finally, the longer-lived persistence of CO(2) in the vicinity of the active centre (i.e., slower self-diffusion) may serve to explain, in part, why carboxylation is the more kinetically favoured on an overall basis compared to oxygenation.

Mechanism of atmospheric CO2 fixation in the cavities of a dinuclear cryptate.

Using density functional theory (DFT) methods, we have investigated two possible mechanisms for atmospheric CO(2) fixation in the cavity of the dinuclear zinc(II) octa-azacryptate, and the subsequent reaction with methanol whereby this latter reaction transforms the (essentially) chemically inert CO(2) into useful products. The first mechanism (I) was proposed by Chen et al. [Chem.-Asian J. 2007, 2, 710], and involves the attachment of one CO(2) molecule onto the hydroxyl-cryptate form, resulting in the formation of a bicarbonate-cryptate species and subsequent reaction with one methanol molecule. In addition, we suggest another mechanism that is initiated via the attachment of a methanol molecule onto one of the Zn-centers, yielding a methoxy-cryptate species. The product is used to activate a CO(2) molecule and generate a methoxycarbonate-cryptate. The energy profiles of both mechanisms were determined, and we conclude that, while both mechanisms are energetically feasible, free energy profiles suggest that the scheme proposed by Chen et al. is most likely.

A theoretical thermodynamic investigation of cascade reactions in dinuclear octa-azacryptates involving carbon dioxide.

This paper investigates the thermodynamics of gas-phase CO(2) cascade uptake-reactions in the form of carbonate or monomethylcarbonate anions in the host cavity of various dinuclear octa-azacryptates of m-CH(2)C(6)H(4)CH(2) and 2,5-furano-spaced hosts, L (1) and L (2) cryptands, using density functional theory (DFT). The cascade process involves two stages, namely the formation of dinuclear cryptate complexes, and the subsequent formation of either µ-carbonato cryptate complexes or µ-monomethylcarbonato cryptates. The geometric and electronic structures were also investigated to determine the parameters that affect the stability of the complexes. Natural bond orbital (NBO) analysis was used to investigate the interactions between the trapped anion and its host. Ion selectivity was studied in terms of the formation of dinuclear cryptate complexes, while the basicity and nucleophilicity of cryptands towards Lewis acids was also studied, and good agreement was found vis-à-vis available experimental data.