Search

The atmospheric degradation mechanism kinetics of chlorotrifluoroethylene (CTFE), which is initiated by OH˙ and results in a variety of chemical oxidation products, were investigated using density functional theory (DFT) with the aug-cc-pVTZ basis set.

In this work, without using any linker or chemical modification of graphene oxide, a zinc oxide immobilized graphene oxide-based catalyst was used for the direct aerobic oxidative conversion of alcohols to the nitriles in water. In the first step, graphene oxide was prepared and then zinc ions were electrostatically adsorbed onto the surface of graphene oxide. In the following step, zinc oxide nanoparticles were generated via in-situ growth in presence of NaOH. It was illustrated that graphene oxide layers can control the size of in-situ generated zinc oxide nanoparticles. Various aromatic/aliphatic/heteroaromatic primary alcohols converted to the nitriles in high yields under O2 balloon with ZnO/GO catalyst. This catalyst can be used for 7 successful consecutive runs without significant loss of activity.

In this investigation at the MN15L/Def2-TZVP level of theory, we present computational evidence indicating that the reaction of 3Σ-g-O2 with spirovinylcyclopropyl oxindole (2) leads to a product called spiro-1,2-dioxolane (2) in its singlet state; this reaction occurs via a stepwise mechanism and its rate-determining step is catalyzed by iodine radicals, which promotes opening of the three-membered ring under dark conditions. The conversion of 2 to 1-benzylindoline-2,3-dione (3) and 2-vinyloxirane (4) takes place via a concerted and slightly asynchronous reaction. Both electron localization function and AIM topological analysis reveal that the step associated with the attack of the 3Σ-g-O2 molecule on the intermediate 3MC characterizes the formation of the only new O2-C3 single bond, which occurs in a stepwise mechanism, in contrast to the Δg-O2 reaction with 15 species.

The kinetic and thermodynamic parameters of Newman–Kwart rearrangement (NKR) of N,N-dimethyl O-arylthiocarbamate into N,N-dimethyl S-arylcarbamate have been evaluated using the Minnesota density functionals (M06-2X and MN15-L) conjugated with the aug-cc-pVTZ basis set and compared with benchmark CBS-QB3 results. Environments of diphenyl ether and o-dichlorobenzene solvents were simulated implicitly by means of the SMD solvation model. The employed temperatures 505 K in diphenyl ether and 413 K in o-dichlorobenzene were more than two times larger than the cross-over temperature, implying shallow tunneling. The evaluated kinetic and energetic parameters using the CBS-QB3 method were in excellent agreement with the experimentally supplied data. The rate constant in diphenyl ether can be expressed by original and modified Arrhenius equations kCBS-QB3/Eckart404-606K = 6.46 × 1012 exp(−19944.6/T) and kCBS-QB3/Eckart404-606K = 1.26 × 1010T0.865 exp(−19516.8/T), respectively. Topological evolution along the reaction has been studied at the B3LYP/CBSB7 level in an o-dichlorobenzene environment using the quantum chemical topology tools. The electron density in C–O and C–S bonds was strongly polarized toward the oxygen and sulfur atoms, respectively, in such a manner that carbonyl and thiocarbonyl bonds cannot be described by Lewis's bonding model. Topological and chemical events along the reaction may be described as: (i) formation of a new monosynaptic basin V(C1) associated with the pseudoradical center on the ipso-carbon atom by means of Fold (F†) type catastrophe, and (ii) transformation of disynaptic basin V(C1,O) into the monosynaptic basin V3(O) associated with the heterolytic rupture of the C1–O bond by means of elliptic umbilic (E) catastrophe, and merging of V3(S) and V(C1) monosynaptic basins into the new disynaptic basin of V(C1,S) associated with the formation of the C1–S bond via usual sharing of the non-bonding electron densities (C1-to-S coupling of pseudoradical centers) by means of a Cusp (C) type catastrophe. The detailed picture of chemical events along the NKR reveals that the electron density flow does not take place in a cyclic and one-way curve, suggesting a non-concerted mechanism.

Pharmaceuticals and personal care products are recognized as new classes of water pollutants that receive considerable attention because of their negative environmental impact on aquatic life and humans. Because microbiological and/or conventional secondary physicochemical treatments cannot completely remove those water pollutants, effective advanced oxidation processes using semiconductor-based photocatalysts are needed to ensure their total elimination in water. Here, we report on the tuning of the morphological structure, light absorption, and photocatalytic activity of Bi2WO6 and Bi2WO6-BiOCl through cerium doping. Non-doped and Ce-doped Bi2WO6 and Bi2WO6-BiOCl powders are synthesized by a hydrothermal method, and their adsorption ability and photocatalytic activity are evaluated for the removal of salicylic acid in the dark and under visible light irradiation, respectively. The adsorption affinities and preferential sites of salicylic acid molecules on non-doped and Ce-doped Bi2WO6, BiOCl, and Bi2WO6-BiOCl are computationally predicted using molecular dynamics simulations. When ethylene glycol is replaced by dilute HCl as a solvent in a hydrothermal system, BiOCl is also formed along with Bi2WO6, confirming the successful formation of a Bi2WO6-BiOCl composite. The flower-like hierarchical structures of Bi2WO6 and Bi2WO6-BiOCl can absorb more photon energy due to multiple scattering, charge carriers can easily transfer to the surface/interface, and mesopores can improve the transfer rate of organic molecules, contributing to the overall enhancement in photocatalytic activity. The Bi2WO6-BiOCl samples show higher photocatalytic activity than that of the Bi2WO6 samples for the degradation of salicylic acid due to the formed p–n heterojunction. The optimum concentration of Ce doping is found to be 1 mol% in the Bi2WO6 and Bi2WO6-BiOCl, promoting the effective separation and transfer of photogenerated charge carriers, resulting in high photocatalytic performance, and the sample exhibited good stability. Fil: Hojamberdiev, Mirabbos. Tokyo Institute Of Technology; Japón Fil: Kadirova, Zukhra C.. Uzbekistan-japan Youth Innovation Center; Uzbekistán Fil: Zahedi, Ehsan. Islamic Azad University; Irán Fil: Onna, Diego Ariel. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; Argentina Fil: Marchi, María Claudia. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; Argentina Fil: Zhu, Gangqiang. Shaanxi Normal University; China Fil: Matsushita, Nobuhiro. Nagoya University; Japón Fil: Hasegawa, Masashi. Tokyo Institute Of Technology; Japón Fil: Aldabe, Sara Alfonsina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; Argentina Fil: Okada, Elena. Tokyo Institute Of Technology; Japón

The kinetics and molecular mechanism of the gas phase degenerate Cope rearrangement (DCR) of bullvalene have been investigated by applying quantum mechanical calculations. Highly accurate energies (CBS-QB3 and CBS-APNO) and RRKM calculations were employed to study the kinetics and ‘fall-off’ behavior. It was found that the DCR of bullvalene (C3v) occurs through a bishomoaromatic transition structure (C2v) with an energy barrier of ∼49 kJ mol−1. The calculated activation energy and enthalpy were in good agreement with the available values in the literature, but lower than those of common Cope rearrangement; this result is related to the high stabilization energy due to the interaction of the allyl fragments in the bishomoaromatic transition structure. The fall-off curve revealed that TST breaks down slightly in estimating the high-pressure limit of the reaction rate and also obtaining the reaction as bimolecular is experimentally impossible. The synergic effect of ELF, NCI, and QTAIM has been used to study the molecular mechanism of the DCR of bullvalene at the B3LYP/6-311G(d,p) level of theory. The catastrophe sequence for DCR of bullvalene was 5-C†[F]2TS[F†]2C-0, which includes the following four steps: (i) homolytic rupture of the C1–C7 bond and formation of two pseudoradical centers on the C1 and C7 atoms; (ii) destruction of the pseudoradical centers; (iii) formation of new pseudoradical centers on the C3 and C5 atoms; and (iv) C-to-C coupling of the pseudoradical centers and formation of a new C3–C5 bond, where the electron density rearrangement takes place in an asynchronous manner.

The kinetic and electron density flows are studied theoretically for the gas phase pyrolysis of cubane via its cage opening to reach bicyclooctatriene and then thermal rearrangement of bicyclooctatriene to produce [8]annulene which is the experimentally observed major product. The observed kinetic data at the MN15-L/maug-cc-pVTZ level of theory were in good agreement with the experimental results as compared to the CBS-QB3 method. The cage opening and the thermal rearrangement steps at the experimentally employed temperature of 520 K were exergonic and exothermic. The atmospheric rate constants calculated by means of the RRKM theory show that the cage opening is the rate-determining step. The temperature dependence of the rate constant for the cage opening step at the MN15-L level can be expressed as log(k/s−1)1barMN15-L = (15.63) − (48.99 kcal mol−1)/RT ln 10. The molecular mechanism of the reactions has been investigated by means of the bonding evolution theory (BET) at the B3LYP/6-311G (d,p) level of theory. The cage opening course is described topologically by cleaving of C1–C2, C4–C8, and C5–C6 single bonds and electron saturation of the C1–C4, C2–C6, and C5–C8 bonds, while the rearrangement of bicyclooctatriene is described by C3–C7 bond rupture, depopulation of C1–C4 and C5–C8 double bonds, and electron saturation of C1–C5, C3–C4, and C7–C8 bonds. Electron density rearrangement along the two successive steps are asynchronous and the sequence of catastrophes can be represented as: η-1-13-C†C†FFFC†C†FFFC†C†-2-6-[C]2C†[F]2[C†]2C†-0.

Atmospheric oxidative degradation of p-chloroaniline (PCA) initiated by OH

In this investigation at the MN15L/Def2-TZVP level of theory, we present computational evidence indicating that the reaction of

Osseointegration of dental, craniofacial, and orthopedic implants is critical for their long-term success. Multifunctional surface treatment of implants was found to significantly improve cell adhesion and induce osteogenic differentiation of dental-derived stem cells in vitro. Moreover, local and sustained release of antibiotics via nanolayers from the surface of implants can present unparalleled therapeutic benefits in implant dentistry. Here, we present a layer-by-layer surface treatment of titanium implants capable of incorporating BMP-2–mimicking short peptides and gentamicin to improve their osseointegration and antibacterial features. Additionally, instead of conventional surface treatments, we employed polydopamine coating before layer-by-layer assembly to initiate the formation of the nanolayers on rough titanium surfaces. Cytocompatibility analysis demonstrated that modifying the titanium implant surface with layer-by-layer assembly did not have adverse effects on cellular viability. The implemented nanoscale coating provided sustained release of osteoinductive peptides with an antibacterial drug. The surface-functionalized implants showed successful osteogenic differentiation of periodontal ligament stem cells and antimicrobial activity in vitro and increased osseointegration in a rodent animal model 4 wk postsurgery as compared with untreated implants. Altogether, our in vitro and in vivo studies suggest that this approach can be extended to other dental and orthopedic implants since this surface functionalization showed improved osseointegration and an enhanced success rate.

This paper presents a machine learning-based guidance (LbG) approach for kinesthetic human-robot interaction (HRI) that can be used in virtual training simulations. Demonstrated positional and force skills are learned to both discriminate the skill levels of users and produce LbG forces. Force information is obtained from virtual forces, which developed based on real computed tomography (CT) data, rather than force sensors. A femur bone drilling simulation is developed to provide a practice environment for orthopaedic residents. The residents are provided with haptic feedback that enable them to feel the variable stiffness of bone layers. The X-ray views of the bone are also presented to them for better tracking of a pre-defined path inside the bone. The simulation is capable of planning a drill path, generating X-rays based on user defined orientation, and recording motion data for user assessment and skill modeling. The knowledge of expert surgeons is also incorporated into the simulation to provide LbG forces for improving the unpredictable motions of the residents. To discriminate the skill level of users, machine learning tools are used to develop surgical expert and resident models. In addition, to improve residents performance, the expert HCRF is used to generate adaptive LbG forces regarding the similarities between residents motions and the expert model. Experimental results show that the learning-based approach is able to assess the skill of users and improve residents performance.

The 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is the most toxic polychlorinated dibenzo-p-dioxin. The OH –initiated oxidation of TCDD has been studied using the density functional, canonical transition state, and canonical Rice-Ramsperger-Kassel-Marcus theories. The kinetic data were corrected for quantum tunneling by the Wigner and Eckart models. All OH addition and hydrogen atom abstraction channels were thermodynamically exergonic. The kinetic and thermodynamic data analysis at the reliable level MPWB1K/MG3S//M06-2X/MG3S indicate that the addition of OH to the carbon atom adjacent to the oxygen atom in dioxin ring leads to the formation of predominant adduct. The calculated bimolecular rate constant for the formation of predominant adduct was ~5.97–6.75 × 10−13 cm3 molecule−1 s−1, its branching ratio was ~0.955, and the overall rate constant for the OH –initiated oxidation of TCDD was ~6.25–7.08 × 10−13 cm3 molecule−1 s−1. The atmospheric lifetime of TCDD determined by OH was ~8.17–9.26 days indicating the TCDD can be categorized as medium lifetime organic pollutant.

In the present work, wetting and interfacial properties of two new kinds of imidazolium-based ionic liquid (IL) nanodroplets, that is, dicationic IL and tricationic IL with respect to a baseline of a traditional monocationic IL on a boron nitride (BN) surface, is studied using classical molecular dynamics simulation. Calculated contact angles of all studied nanodroplets on the BN surface are lower than 90°, which demonstrate favorable wettability of the studied ILs on the BN sheet. Density profiles show an enhancement in density of both cations and anions at the BN surface for all studied droplets. Orientational analysis revealed that for monocationic ionic liquids, the imidazolium ring of cations lies parallel to the BN surface, while for multicationic ILs (dication and trication), the perfect parallel arrangement could not be observed. Identification of the truly interfacial molecule method has been used to analyze the structure and dynamics of the ions at the interface. It shows that the survival proba...

Underground dams are constructions that prevent the natural flow of ground water and create underground water resources. Although lateral-flow volume is one of the main criteria to locate an underground dam, this factor is ignored in the most studies. In this research, the water balance equation was simulated using the SWAT model in the Daroongar watershed (northeastern Iran), and the paths of subsurface water flows were identified. Continuing by giving the weight to an 11-layer analytical network process (ANP), potential suitable locations for the construction of underground dams were determined. With the implementation of the SWAT model in the Daroongar watershed, R2, bR2, and NS (Nash Satklyf) coefficients were 0.77, 0.75, and 0.68, respectively, in the calibration phase; in the validation phase, they were 0.71, 0.67, and 0.61 in the same order. All these coefficients show that the efficiency of the SWAT model in simulating water balance is acceptable. Results of the sensitivity analysis of the SWAT model show 27 effective parameters, where the runoff curve number (CN2) was identified as the most important parameter. The results of the ANP model prove that subsurface flow, weighing 0.131, includes the most weight allocated. Results from the ANP model indicated that this is necessary for determining the extent of subsurface flow using the SWAT model. In addition, the reservoir volume and runoff volume, respectively, with a weight of 0.109 and 0.101 are more important than other factors. As a result, the greater the current subsurface stream, the more important it is in relation with other streams. The results showed that streams with ranks 3 and 4, which are located on slopes less than 15%, are suitable for the construction of underground dams.

The atmospheric oxidation mechanism of imidazole initiated by hydroxyl radicals is investigated via OH-addition and H-abstraction pathways by quantum chemistry calculations at the M06-2X/aug-cc-pVTZ level of theory coupled with reaction kinetics calculations using statistical Rice-Ramsperger-Kassel-Marcus (RRKM) theory and transition state theory (TST). It was found that OH addition proceeds more rapidly than H-abstraction by several orders of magnitude. Moreover, H-abstraction reactions with submerged barriers exhibit positive temperature dependence. Effects of reaction temperature and pressure on the reaction between imidazole and OH radicals are studied by means of RRKM calculations. Effective rate coefficients involve two-step mechanisms. According to the experiment, the obtained branching ratios show that the kinetically most efficient process corresponds to OH addition onto a carbon atom which is adjacent to a nitrogen atom having a lower energy barrier. These ratios also reveal that the regioselectivity of the oxidation reaction decreases with increasing temperatures and decreasing pressures. Because of negative activation energies, pressures larger than 100 bar are required to reach the high pressure limit. The atmospheric lifetime of imidazole in the presence of OH radicals is estimated to be ∼4.74 days, based on the calculated overall kinetic rate constant of 1.22 × 10-12 cm3 molecule-1 s-1 at a pressure of 1 bar and nearly ambient temperature. NBO analysis demonstrates that the calculated energy barriers are dictated by charge transfer effects and aromaticity changes because of the delocalization of nitrogen lone pairs to empty π* orbitals.

The complete theoretical study of thermal Curtius rearrangement of syn-syn and syn-anti conformers of oxalyl diazide, in the gas phase and in solution has been established for the first time. The inexplicit solvent effect was taken into account via the self-consistent reaction field (SCRF) method. The gas and solution phases of all optimized geometries of the mentioned conformers associated with the Curtius rearrangement along the concerted and stepwise pathways were reported using the polarized continuum model and non-electrostatic terms from the SMD universal solvation model. The Curtius rearrangement of syn-syn and syn-anti conformers was taken place via concerted and stepwise pathways, respectively. The syn-syn conformer of oxalyl diazide is more stable than the syn-anti conformer in the gas phase and solution, and rearranged to syn-carbonyl azide isocyanate via an exergonic concerted mechanism with a single transition state. Nevertheless, the rearrangement of syn-anti conformer occurred through the two transition states and an intermediate, which the first and second steps are endergonic and exergonic, respectively. Theoretical results point out that the concerted pathway is predominant with 102-106 and 104-105 times faster than the stepwise mechanism in gas phase and solution, respectively. Topological analysis of the electron localization function at the B3LYP/6–311++G (2d,d,p) level of theory indicate that the catastrophe sequence 1-6-C†TSC†F C†C-0 begins with the N4–N5 bond breaking, elimination of nitrogen molecule and increasing of non-bonding monosynaptic attractor on N4 atom, and then changing of topological signature of C2–N4 bond, breaking of C1–C2 bond, and formation of pseudo-radical centers on C1 and C2 atoms. Subsequently, annihilation of pseudo-radical centers on the C1 atom, change of topological signature of C2–N4 and formation of C1–N4 bond were executed. The obtained results of ELF calculations show that the reaction takes place via a concerted mechanism but highly asynchronous process.

The gas-phase β-elimination kinetics of 2,2-difluoroethyltrifluorosilane (1), 2,2-difluoroethylmethyldifluorosilane (2), 2,2-difluoroethyldimethylfluorosilane (3), and 2,2-difluoroethyltrimethylsilane (4) have been investigated computationally using M06-2x exchange-correlation functional as well as the benchmark CBS-QB3 quantum chemical approach. The obtained energy profile has been enhanced with kinetic calculations using statistical Rice-Ramsperger-Kassel-Marcus (RRKM) theory and transition state theory (TST). The calculated results are in good agreement with the available experimental data which obtained by the CBS-QB3 approach. The comparison between all our calculations and experiments indicates that a thermodynamically-controlled reaction that gives more stable products derived from the compound 2 species will be the vinyl fluoride and methyltrifluorosilane species, whereas the elimination of compound 1 into the vinyl fluoride and silicon tetrafluoride species is favorable process from kinetic point of view. In proportion to rather larger barrier heights, pressures where P > 10―4 bar are insufficient to ensure a saturation of the calculated rate constant compared with the RRKM unimolecular rate kinetics (in high-pressure limit). Natural bond orbital analysis revealed that in accordance with an increase of barrier height from compounds 1 to 4, the HOMO-LUMO energy-gaps decreases. Furthermore, the obtained order of barrier heights could be explained by the number of electron-withdrawing fluorine atoms attached to the silicon atom. The occupancies of σC1―F3 bonding orbital for the studied compounds are as follows: 1>2>3>4 and those of σ*C1―F3 antibonding orbital increase in the opposite order (4>3>2>1) by NBO analysis. This fact explains a comparatively easier elimination of the σC1―F3 bond in compound 1 compared to the other compounds. The calculated data reveal that the polarization of the C1―F3 bond in the sense C1δ+–F3δ− is the determining factor in the elimination reaction of the studied compounds.

The thermal decomposition kinetics of allyl methyl amine, allyl methyl ether, and allyl methyl sulfide in the gas phase has been studied theoretically using the M06-2x/aug-cc-pVTZ quantum chemical approach. The observed activation parameters are consistent with a concerted unimolecular mechanism involving a non-planar cyclic six-membered transition state. Based on the optimized ground state geometries, a natural bond orbital analysis of donor–acceptor interactions reveals that the stabilization energies corresponding to the electronic delocalization from the lone-pair (LP) non-bonding orbitals on the heteroatom to the neighboring $$\sigma_{{{\text{C2}} - {\text{C3}}}}^{*}$$ antibonding orbitals decrease from allyl methyl amine to allyl methyl sulfide. This delocalization fairly explains the increase of occupancies of LP orbitals on the heteroatom from allyl methyl sulfide to allyl methyl amine. The results also suggest that the kinetics of the thermolysis of the studied compounds are dominated by $${\text{LP}}\, \to \,\sigma^{*}$$ electronic delocalization effects. Analysis of bond order, bond indices, and synchronicity parameters demonstrates that these reactions proceed through a concerted and slightly asynchronous mechanism.

The approach presented here is an unprecedented insight into the understanding of kinetics and molecular mechanism of thermal Curtius rearrangement of 3-oxocyclobutane-1-carbonyl azide. Curtius rearrangement can proceed via concerted and stepwise mechanisms. The CBS-QB3 and CBS-APNO composite methods indicated that concerted pathway is dominant and 104–105 times faster than stepwise path. The bonding evolution theory analysis at the B3LYP/6-311G(d,p) revealed that the reaction via concerted pathway can be described with catastrophe sequence 9-CF†C†TSFC†FC†C-0 by the following chemical events: (a) change of topological signature of N2 N3 bond; (b) increasing the number of non-bonding monosynaptic attractor on N1 atom; (c) breaking of N1 N2 bond and extrusion of nitrogen molecule; (d) decreasing the number of non-bonding monosynaptic attractors on N1 atom; (e) breaking of C4 C5 bond and formation of pseudoradical centers on the C4 and C5 atoms; (f) annihilation of pseudoradical center on the C5 atom; (g) change of topological signature of N1 C5 bond; and (h) formation of N1 C4 bond. Along the reaction course electron flow redistribution is asynchronous and bond breaking/forming do not takes place simultaneously demonstrating that the reaction is concerted yet highly asynchronous process.

The Leuckart–Wallach reductive amination reaction in clandestine amphetamine synthesis is the most popular, simple, rapid, and safe non-metal reduction route, in which its mechanism is not known with certainty. The Minnesota 2006 exchange correlation functional M06-2X in conjugation with aug-cc-pVTZ basis set and SMD universal solvation model have been used to elucidate the kinetics and mechanism of the Leuckart–Wallach reaction for the formation of amphetamine via a five-step pathway mechanism in 1-butanol and benzene solvents. The unimolecular and bimolecular rate constants were calculated at the experimentally employed temperature 403.15 K using canonical transition state theory corrected by the quantum tunneling factors. The overall reaction is thermodynamically spontaneous and kinetically second order (first order in ammonium formate and first order in phenyl-2-propane) which is in agreement with experimental results. In the following, drug–DNA interaction in four different models has been studied in the water solvent using the mPW1B95/6–31G* level of theory. The mPW1B95/6–31G* energies were corrected for the basis set superposition error and the underestimation of London dispersion interactions by adding the gCP and D3(BJ) correction terms, respectively. According to the interaction energies, topological analysis of electron localization function and localized orbital locator, interaction of amphetamine with GpC·CpG base-pair step of DNA is non-covalent in nature. Non-covalent interaction index plots indicated that there are weak van der Waals and strong stabilizing hydrogen bond attractions between the drug and DNA. The presence of strong stabilizing hydrogen bond attractions is the responsible for the higher negative interaction energies in the interaction models including hydrogen bonds between amphetamine and DNA.

A joint application of bonding evolution theory (BET) and non-covalent interaction (NCI) analysis provides a powerful tool to explain the molecular mechanism of organic reactions. Thio-Claisen rear...

The crystal structures, electro–optical properties, and charge carrier effective masses of Cs 2 TeW 3 O 12 and Cs 2 TeMo 3 O 12 with hexagonal, polar and non–centrosymmetric crystal structure were investigated based on density functional theory. Cs 2 TeW 3 O 12 and Cs 2 TeMo 3 O 12 are found to be indirect K (1/3, 1/3, 0) → G (0, 0, 0) band gap semiconductors ( E g > 3 eV) with small effective masses of photogenerated charge carriers. The mixing of octahedrally coordinated d ° transition metal cations (W 6+ and Mo 6+ ) with the filled p orbitals of the oxygen ligands leads to the formation of some W 5+ /Mo 5+ sites and splitting of d orbitals into the partially filled t 2g ( dxy , dyz , and dzx ) orbitals and empty e g ( dz 2 and dx 2 – y 2 ) orbitals. The top of the valence bond is mainly contributed by O 2 p orbital of the oxygen ligands mixed with the partially filled t 2g orbitals of W 5 d /Mo 4 d , while the conduction band mainly consists of empty e g orbitals of W 5 d /Mo 4 d with a little contribution of O 2 p orbitals. The dielectric function exhibits a slight anisotropic behavior and optical absorption peak for Cs 2 TeW 3 O 12 and Cs 2 TeMo 3 O 12 belonging to the strong electronic transition O 2 p → W 5 d /Mo 4 d within the octahedral units. According to the estimated valence band and conduction band edges, Cs 2 TeW 3 O 12 and Cs 2 TeMo 3 O 12 can be applied as visible−light−responsive photocatalysts for the decomposition of organic pollutants and dye molecules. Also, Cs 2 TeMo 3 O 12 can be used in water splitting for hydrogen generation but Cs 2 TeW 3 O 12 requires further experimental studies to confirm its ability for water splitting.

The thermal decomposition kinetics of 2-chloroethylsilane and derivatives in the gas phase has been studied computationally using density functional theory, along with various exchange-correlation functionals (UM06-2x and ωB97XD) and the aug-cc-pVTZ basis set. The calculated energy profile has been supplemented with calculations of kinetic rate constants under atmospheric pressure and in the fall-off regime, using transition state theory (TST) and statistical Rice–Ramsperger–Kassel–Marcus (RRKM) theory. Activation energies and rate constants obtained using the UM06-2x/aug-cc-pVTZ approach are in good agreement with the experimental data. The decomposition of 2-chloroethyltriethylsilane species into the related products [C2H4 + Et3SiCl] is characterized by 6 successive structural stability domains associated to the sequence of catastrophes C8H19SiCl: 6-C†FCC†[FF]-0: C6H15SiCl + C2H4. Breaking of Si–C bonds and formation of Si–Cl bonds occur in the vicinity of the transition state. All calculations presented in this work have been performed at the Flemish Supercomputer Center (Vlaams Supercomputer Centrum). This cluster has been financed by budgets obtained from the Katholieke Universiteit Leuven, as well as from individual contributions by users, and funding obtained from the Hercules foundation and the Flemish government.

The kinetics and mechanisms of pyrolysis of 1,3-dihydroisothianaphthene-2,2-dioxide toward benzocyclobutene have been theoretically studied using canonical transition state theory (CTST), statistical Rice–Ramsperger–Kassel–Marcus (RRKM) theory, and bonding evolution theory (BET) in conjugation with M06-2X/aug-cc-pVTZ calculations. The CTST slightly breaks down to estimate the reaction rate of the cheletropic extrusion. RRKM results indicated that the cheletropic extrusion and electrocyclic reaction require energy barriers of 171.3 and 122.2 kJ/mol to be overcome; and can be characterized respectively by 7 and 3 phases associated to the sequence of catastrophes C 8 H 8 SO 2 ( 1 ): 7-[FF]C † C † FFF-0: C 8 H 8 + SO 2 and C 8 H 8 ( 2 ): 3-[F † F † ]C-0: C 8 H 8 ( 3 ). For the cheletropic extrusion, breaking of the C 7 –S and C 8 –S bonds begins respectively at Rx = −2.7434 amu 1/2 Bohr and Rx = −1.7458 amu 1/2 Bohr, and formation of the sulfur dioxide is completed at Rx = −0.2494 amu 1/2 Bohr. For the electrocyclic reaction, formation of new C 7 –C 8 bond occurs at Rx = 1.6214 amu 1/2 Bohr from C- to C- coupling between the generated pseudoradical centers at Rx = 0.1474 amu 1/2 Bohr on the terminal carbon atoms.

Most metal forming processes use lubricants based on mineral oils as an intermediate medium to reduce friction and wear. To avoid the well-known drawbacks of oil lubrication, a novel and environment friendly lubrication system for deep-drawing processes was demonstrated at the University of Stuttgart. Liquid carbon dioxide and gaseous nitrogen are being used as volatile lubrication during the deep-drawing process, locally injected at high pressure through laser-drilled microholes. This new tribological system provides a significantly enlarged working range and at least 15% larger drawing depths compared to conventional oil lubrication.

To expand the family of transition metal oxynitride perovskites, the two-step synthesis of a series of tungsten-based metal oxynitride perovskites (EuW(O,N)3, NdW(O,N)3, PrW(O,N)3, LaW(O,N)3, and SrW(O,N)3) and their visible-light-driven photocatalytic water oxidation activity with the assistance of CoOx (2 wt% Co) cocatalyst were studied in this work. The XRD results revealed that the cubic perovskite LnW(O,N)3 (Ln = Pr, Nd, and Eu) and SrW(O,N)3 phases and tetragonal perovskite LaW(O,N)3 phase were successfully synthesized by nitriding their corresponding oxide precursors at 900 °C for 10–25 h under an NH3 flow, with minor secondary phases in only PrW(O,N)3 and NdW(O,N)3. The highly porous structures of EuW(O,N)3, LaW(O,N)3, and SrW(O,N)3 were formed from the segregation of nanocrystals with average sizes of 140, 92, and 160 nm, respectively. The surfaces of the NdW(O,N)3 and PrW(O,N)3 crystal structures were covered with plate-like crystals which can be identified as W5N4. No clear absorption edges were observed in the UV–Vis diffuse reflectance spectra of the tungsten-based metal oxynitrides owing to the extensive amount of reduced tungsten species (W5+ and W4+) or metallic tungsten and anion deficiency. Within 5 h of the photocatalytic water oxidation half-reaction, the CoOx-loaded SrW(O,N)3 crystal structures exhibited the highest photostability and O2 evolution rate of 3.3 μmol h−1 compared with CoOx-loaded LnW(O,N)3 (Ln = La, Pr, Nd, and Eu) crystal structures due possibly to the highest O/N ratio and more positively positioned top of valence band of SrW(O,N)3. The present work is expected to stimulate research into the development of more stable and efficient tungsten-based metal oxynitride perovskites in the future.

The cheletropic elimination process of N2 from (2,5-dihydro-1H-pyrrol-1-ium-1-ylidene) amide (C4H6N2) has been studied computationally using density functional theory, along with the M06-2X/aug-cc-pVTZ level of theory. The calculated energy profile has been supplemented with calculations of kinetic rate constants using transition state theory (TST) and statistical Rice–Ramsperger–Kassel–Marcus (RRKM) theory. This elimination process takes place spontaneously with an activation energy around 33 kJ/mol. Pressure dependence of the rate constants revealed that the TST approximation breaks down and fall-off expression is necessary for the kinetic modeling. At temperatures ranging from 240 to 360 K and atmospheric pressure, the unimolecular rate constant is evaluated from RRKM theory as $$k_{{(240 - 360\,{\text{K}})}}^{{1.0{\text{atm}}}} = 1.0249 \times 10^{12} \times {\text{e}}^{{ - \frac{{33.11\;{\text{kJ}}/{\text{mol}}}}{RT}}} \,{\text{s}}^{ - 1}$$ . Bonding changes along the reaction coordinate have been studied using bonding evolution theory. Electron localization function topological analysis reveals that the cheletropic elimination is characterized topologically by four successive structural stability domains (SSDs). Breaking of C–N bonds (Rx = 0.1992 amu1/2 Bohr) and the other selected points separating the SSDs along the reaction coordinate occur in the vicinity of the transition state.

Conceptual density functional theory, including chemical hardness, electronic chemical potential, global and local electrophilicity index and Fukui functions, is used to predict reactivity and regioselectivity of 1,3-dipolar cycloadditions (13DCs) between five aryl azides (1–5) and an electron-deficient alkyne at the B3LYP/6-31G(d,p) level. Two reaction paths (a) and (b) are considered which result in the corresponding regioisomeric 1,2,3-triazoles P(1-5)a and P(1-5)b, respectively. All the 13DCs proceed via rather asynchronous TSs and the path (b) is clearly more synchronous than the path (a). All the reactions are high exoergic [∆Go = −45.1 to −51.4 kcal/mol for path (a) and −47.7 to −55.9 kcal/mol for path (b)] with the moderate and nearly similar activation barriers (E a = 15.4–16.7 kcal/mol) referring a relatively low regioselectivity. All reactivity descriptors but one clearly suggest that path (a) is somewhat preferred over path (b). FMO interactions occur between HOMO13DP and LUMODPh due to the corresponding lower energy gap. All the reactions considered in this work classified as polar 13DCs with NED character. Our theoretical results are in good agreement with those reported experimentally.

We report on the synthesis of new Dion–Jacobson phase three-layer perovskite CsBa2Ta3O10 crystals by conventional solid-state reaction and fabrication of their nitrided Ba2Ta3O10 nanosheets via a nitridation–protonation–intercalation–exfoliation route for visible-light-driven photocatalytic water splitting application. The two-dimensional crystal structure of CsBa2Ta3O10 refined by the Rietveld refinement method belongs to the simple tetragonal system and consists of corner-shared distorted TaO6 octahedra and Ba cations in cuboctahedral sites forming triple-layer perovskite slabs. The valence and conduction band edge potentials estimated by density functional theory with respect to vacuum scale and normal hydrogen electrode indicate that CsBa2Ta3O10 is a UV-light-active semiconductor that can be used for photocatalytic water splitting and decomposition of organic pollutants. The projected electronic wave functions contour plot of CsBa2Ta3O10 in the (1 0 0) plane exhibited two different Ta–O bonds. The nit...