Influence of sulfation conditions on the acidic and catalytic properties of sulfated alumina in isobutane alkylation with butylenes and <Emphasis Type="Italic">n</Emphasis>-pentane isomerization

The influence of the sulfation parameters (the source and concentration of sulfate ions) and the calcination temperature on the acidic and catalytic properties of sulfated alumina in the alkylation of isobutane with butylenes and n-pentane isomerization was studied. IR spectroscopy of adsorbed probe molecules and temperature-programmed desorption of ammonia were used to characterize the acidic properties of the catalysts. An increase in the content of sulfate groups to the value corresponding to a formal value of the monolayer capacity increases the activity of alkylation and the concentration of strong Brönsted sites. The dependence of the stability of activity in alkylation on the sulfate group concentration is extreme with a maximum at the concentration close to the monolayer capacity. It was concluded from the IR spectroscopic data that the decrease in the stability of activity with the further increase in the content of sulfate groups is due to an increase in the concentration of strong Lewis sites and/or an increase in the surface density of strong Brönsted sites. The absence of the correlation between the catalytic behavior of sulfated alumina samples in n-pentane isomerization and acidity indicates that paraffin activation on these samples occurs via the non-acidic mechanism.     

Effect of the structure of the <Emphasis Type="Italic">ortho</Emphasis>, <Emphasis Type="Italic">meta</Emphasis>, and <Emphasis Type="Italic">para</Emphasis> isomers of perhydroterphenyl on their reactivity in heterogeneous catalytic dehydrogenation

The kinetics of the dehydrogenation of the individual ortho, meta, and para isomers of perhydroterphenyl and their mixtures over a (3 wt % Pt)/C catalyst has been investigated in a flow reactor at 280–340°C. The rate of the isomerization of the stereoisomers of the initial substrate (perhydroterphenyl) and terphenyl dehydrogenation products has an effect on the hydrogen release kinetics. The highest reactivity in isomerization is shown by the ortho isomer. The largest amount of hydrogen (7.0 wt %) is released in the dehy-drogenation of perhydro-meta-terphenyl and perhydro-para-terphenyl, whose conversion at 320°C is 96%.     

Catalytic hydrolysis of α-amino esters in the presence of chiral palladacycles

The rate of hydrolysis of esters derived from optically active α-amino acids, catalyzed by chiral cyclopalladated benzylamines, depends on the configuration of chiral centers in the substrate and catalyst. The catalytic hydrolysis of sulfur-containing amino esters follows an intramolecular mechanism, and the difference in the reaction rates for the stereoisomers increases in going from ortho-palladated primary benzylamines (k _S/k _R = 1.1) to tertiary amines (k _S/k _R = 1.5); the strongest catalytic effect is observed for an ester and a complex with the same absolute configuration of the chiral centers. The efficiency of intermolecular catalysis is greater for a complex and ester with opposite absolute configurations of the chiral centers, and the rate constants of catalytic hydrolysis for two pairs of stereoisomers coincide within experimental error. The maximal difference in the reaction rates is observed for cyclopalladated secondary benzylamines; it reaches 2.3 for the phenylalanine ester.     

Comparison of catalytic performance of synthesized EU-1 zeolite with dealuminated EU-1 zeolite for <Emphasis Type="Italic">m</Emphasis>-xylene isomerization reaction

EU-1 zeolite was synthesized with high purity by a hydrothermal method and under optimum conditions: synthesis time 72 h, temperature 200°C, and aging time 12 h. Then, the synthesized EU-1 zeolite was modified by dealumination with nitric acid and the changes of the properties such as surface area, pore volume, and Si/Al ratio were investigated. The catalytic performance of these two catalysts was studied and compared with a commercial mordenite catalyst for meta-xylene isomerization reaction in a fixed bed reactor. The results showed that the modification of catalyst with acid increases Si/Al ratio from 25 to 50 due to the removal of a number of aluminium atoms from the framework of zeolite. Also the catalyst surface area increased from 300.237 m² g^?1 for EU-1 to 333.639 m² g^?1 for modified EU-1. According to results, the modified Eu-1 had higher para/ortho ratio, meta-xylene conversion, and para-xylene yield than EU-1 and commercial mordenite in the meta-xylene isomerization reaction.     

Synthesis of pyranopyrazoles,benzopyrans, amino-2-chromenes and dihydropyrano[<Emphasis Type="Italic">c</Emphasis>]chromenes using ionic liquid with dual Brønsted acidic and Lewis basic sites

An efficient ionic liquid with both Brønsted acidic and Lewis basic sites, namely 1,4-dimethyl-1-(4-sulphobutyl)piperazinium hydrogen sulphate (IL1), was synthesised and characterised. IL1 is a “green”, homogeneous and reusable catalyst for: i) the synthesis of pyranopyrazoles (Va-Vj)and benzopyrans (VIa-VIj and VIIa-VIIf) at ambient temperature under solvent-free conditions and ii) the synthesis of amino-2-chromenes (VIIIa-VIIIi and IXa-IXi) and dihyropyrano[c]chromenes (Xa-Xi) at 80 °C under solvent-free conditions. The reactions were rapid with excellent product yields. In addition, the double Brønsted acid, 1,4-dimethyl-1,4-bis(4-sulphobutyl)piperazinium hydrogen sulphate (IL2), was prepared to evaluate the cooperation efficiency of their Brønsted acidic and Lewis basic sites as compared with the double Brønsted acidic sites in IL1.     

Iridium–nickel composite oxide catalysts for oxygen evolution reaction in acidic water electrolysis

A series of Ir_1–xNi_xO_2–y (0 ≤ x ≤ 0.5) composite oxides have been prepared by a simple pyrolysis method in ethanol system and used as the electrocatalysts for OER in acidic medium. The materials have been characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF) and scanning electron microscopy (SEM). The electrochemical performances of these Ir_1–xNi_xO_2–y composite catalysts are evaluated by cyclic voltammetry (CV) and steady-state measurements. The resulting oxides with the Ni content (x) less than 0.3 have a complex nature of metal Ir and rutile structure IrO₂ which is similar to the Ir oxide prepared by the same approach and possess the contracted lattice resulted from the Ni-doping. Although the addition of Ni reduces the electroactive surface areas due to the coalescence of particles, the catalytic activity of the Ir_1–xNi_xO_2–y (0 < x ≤ 0.3) catalysts is slightly higher than that of the pyrolyzed Ir oxide. Regardless of the surface area difference, the intrinsic activity first increases and then decreases with the Ni content in Ir_1–xNi_xO_2–y catalysts, and the intrinsic activity of Ir_0.7Ni_0.3O_2–y catalyst is about 1.4 times of the Ni-free Ir oxide mainly attributed to the enhancement of conductivity and a change of the binding energy as increasing amount of the incorporated Ni with respect to the pure IrO₂. The Ir_0.7Ni_0.3O_2–y catalyst shows a prospect of iridium-nickel oxide materials in reducing the demand of the expensive Ir oxide catalyst for OER in acidic water electrolysis.     

Isomerization of Xylenes in the Presence of Pt-Containing Catalysts Based on Halloysite Aluminosilicate Nanotubes

Pt-containing catalysts based on halloysite aluminosilicate nanotubes and ZSM-5 zeolite were synthesized. The structure of the materials was confirmed by low-temperature nitrogen adsorption/desorption and by transmission electron microscopy. The activity and selectivity of the synthesized catalysts based on micromesoporous supports in isomerization of the xylene reforming fraction was studied on a flow-through laboratory installation with a fixed catalyst bed in the temperature interval 360–440°С at elevated hydrogen pressure. The influence exerted by the textural characteristics of the support and acidity of the materials on the catalyst activity in isomerization of o- and m-xylenes and of ethylbenzene with the aim of obtaining p-xylene was studied.     

Efficient and selective oxidation of alcohols with <Emphasis Type="Italic">tert</Emphasis>-BuOOH catalyzed by a dioxomolybdenum(VI) Schiff base complex under organic solvent-free conditions

The catalytic activity of dioxidobis{2-[(E)-p-tolyliminomethyl]phenolato}molybdenum(VI) complex was studied, for the first time, in the selective oxidation of various primary and secondary alcohols using tert-BuOOH as oxidant under organic solvent-free conditions at room temperature. The effect of different solvents was studied in the oxidation of benzyl alcohol in this catalytic system. It was found that, under organic solvent-free conditions, the catalyst oxidized various primary and secondary alcohols to their corresponding aldehyde or ketone derivatives with high yield. The effects of other parameters such as oxidant and amount of catalyst were also investigated. Among different oxidants such as H₂O₂, NaIO₄, tert-BuOOH, and H₂O₂/urea, tert-BuOOH was selected as oxygen donor in the oxidation of benzyl alcohol. Also, it was found that oxidation of benzyl alcohol required 0.02 mmol catalyst for completion. Dioxomolybdenum(VI) Schiff base complex exhibited good catalytic activity in the oxidation of alcohols with tert-BuOOH under mild conditions. In this catalytic system, different primary alcohols gave the corresponding aldehydes in good yields without further oxidation to carboxylic acids.     

Structure of valence band in cluster model for cytochrome-<Emphasis Type="Italic">c</Emphasis>-oxidase active centers

The electron structure of cluster model for active centers of cytochrome-c-oxidase has been calculated by DFT (PBE) method in 6-31G basis. The cluster model was constructed on the basis of experimental PDB-structure and included 1105 hemoprotein atoms. The valence band ceiling of cytochromeoxidase active centers is shown to be formed by the atoms of carbon and nitrogen from porphyrin ring of cytochrome heme a₃ and atoms of carbon and nitrogen from imidazol moieties of histidine connected with Cu atom in cytochrome a₃. D-orbitals of Cu and Fe atoms from heme a₃ and d-orbital of Fe atom from heme a contribute mainly to the orbital group. A conclusion is made that the catalytic activity of the structure is determined by these two types of orbitals. Cu d-orbitals of cytochrome a are substantially low in energy. It is suggested that Cu atoms of cytochrome a shift the chemical potential of d-orbitals belonging to the active center that results in their easier electron accepting and releasing. This can be a decisive factor in the electron transport process.     

Gas-phase and supercritical <Emphasis Type="Italic">n</Emphasis>-pentane isomerization on H-mordenite

The skeletal isomerization of supercritical n-pentane on the H form of mordenite under flow conditions was studied for the first time. It was found that the conversion of supercritical n-pentane was 30–35% at 90% selectivity for isopentane at 260°C, 130 atm, and a liquid hourly space velocity of 30 h^?1. The catalyst was deactivated as the temperature was increased above 280°C. According to differential thermal analysis data, the deactivation was related to the deposition of condensation products on the surface. The resistance of the H form of the zeolite to poisoning in n-pentane isomerization in a gas phase at 1–8 atm was lower than that under supercritical conditions. It was found that H-mordenite deactivated under gas-phase reaction conditions at 260°C and 8 atm can be regenerated by passing to supercritical isomerization conditions (260°C and 130 atm).     

Kinetic analysis of the thermal oxidative degradation of upper peat

Differential thermogravimetric analysis was used to study the thermal oxidative degradation of peat samples from different districts of the Ivanovo Region. The study was performed in nonisothermic conditions. It was found that the thermal oxidative processes involve a few steps. Kinetic characteristics [activation energy (E_a), preexponential factor (ln A), and reaction order (n)] were estimated for each step. It was found that the limiting stage of the entire process is a chemical reaction. The resulting data can be used to develop prognostic models for peatbog combustion.     

Kinetics of the Acid-Base Interaction between Tetra(4-<Emphasis Type="Italic">tert</Emphasis>-butyl)phthalocyanine and Nitrogen-Containing Bases in Dimethyl Sulfoxide

Specific features of the acid-base interaction of tetra(4-tert-butyl)phthalocyanine with cyclic and acyclic nitrogen-containing bases in dimethyl sulfoxide are studied. The effect of pK _a of proton-withdrawing molecules, basicity of a medium, and steric screening of acidic NH centers on the kinetic parameters of formation of proton-transfer complexes stable in time is shown.     

Enantioselective catalysis of Suzuki reaction with planar-chiral <Emphasis Type="Italic">CN</Emphasis>-palladacycles: competition of two catalytic cycles

The investigations of the catalysis of atroposelective Suzuki reaction with chiral CN-palladacycles showed that two competing catalytic cycles operate in this process, the relative contributions of each of them depend on the structure of the catalyst and reaction conditions. The reactions in aprotic medium at reduced temperature predominantly follow the pathway, in which the structure of palladacycle was retained, thus providing enantioselectivity up to 53% ee, when a nonmetallocene planar-chiral iminate CN-dimer was used as the catalyst. The structure of the μ-iodide cyclopalladated CN-dimer recovered upon reaction completion was confirmed by X-ray diffraction and spectroscopic studies of its triphenylphosphine derivative.     

Acidic functionalized ionic liquids as catalyst for the isomerization of α-pinene to camphene

An acidic functionalized ionic liquids (ILs) [HSO₃-(CH₂)₃-NEt₃]Cl-ZnCl₂ was synthesized and used to catalyze the isomerization of α-pinene in a homogeneous system. The optimum conditions for isomerization were obtained as follows: n(α-pinene):n(ILs) = 9:1, reaction temperature 140 °C, and reaction time 4 h, α-pinene 0.04 mol. Under the optimal conditions, the conversion of α-pinene was 97.6 % and the selectivity for camphene could reach 64.8 %. In addition, the catalyst could be easily separated by centrifugation after the isomerization completely finished. When the ILs were repeatedly used for four times, the conversion of α-pinene and the selectivity for camphene were still excellent, indicating the superb recycle ability of the acidic functionalized ILs catalyst.     

The influence of water on the isomerization of α-pinene in a supercritical aqueous-alcoholic solvent

The influence of water as a cosolvent and catalyst of the isomerization of α-pinene in a supercritical aqueous-alcoholic (ethanol) solvent was studied experimentally. At T = 657 K and p = 230 atm, an increase in the concentration of water in the reaction mixture was found to increase the rate of the reaction and its selectivity with respect to the desired product, limonene. Water exhibited the properties of an acid catalyst because of its ionization. Mathematical experimental data processing was performed to evaluate and separate the contributions of the radical and ionic paths to the total rate of the reactions that occurred during the thermal isomerization of α-pinene.     

Catalyst for the oxidation of sulfur-containing compounds based on a polyamide membrane modified with cobalt phthalocyanine

The catalytic activity of phthalocyanine metal complex immobilized on the surface of a porous polyamide membrane is studied in the oxidation reaction of n-propyl mercaptan. Since noncatalytic oxidation is possible in the presence of oxygen, the kinetics of n-propyl mercaptan oxidation is analyzed as its aqueous alkaline solution passes through unmodified membranes. Characteristics of the catalyst’s performance are selected to evaluate the efficiency of the catalytic process. It is shown that the modified membranes with pore diameters of 1 and 2 μm are the most effective catalysts.     

The first principle computational study for the competitive mechanisms of oxidative aromatization of 2-substituted imidazolines using KMnO<Subscript>4</Subscript>/SiO<Subscript>2</Subscript>

The efficiently oxidized various types of 2-substituted imidazolines to the corresponding imidazoles using potassium permanganate supported on silica gel (KMnO₄/SiO₂) under mild conditions and at room temperature have been reported before. In this study, the competitive concerted, catalytic stepwise (E ₁ cb′ _Cat .) and E ₁ cb′ mechanisms of the oxidative aromatization process of 2-imidazolines to the corresponding imidazoles using KMnO₄/SiO₂ have been theoretically investigated by DFT-B3LYP/6-31G** method. The achieved data from this computational study confirmed that the reaction occurs by stepwise E ₁ cb′ mechanism on the basis of the anomeric effect.     

Highly efficient mesoporous WO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/KIT-6 catalysts for oxidative desulfurization of dibenzothiophene with hydrogen peroxide

Oxidative desulfurization (ODS) of organic compounds containing sulfur element from a model oil was performed using tungsten oxide catalysts supported on mesoporous silica with cubic Ia3d mesostructure, well-defined mesopores (7.2 nm), high surface area (719 m²/g), and three-dimensional pore network (WO _x /KIT-6). The prepared WO _x /KIT-6 catalysts (5–20 wt% WO _x ) were characterized by X-ray diffraction analysis, N₂ sorption measurements, electron microscopy, H₂-temperature programmed reduction, Raman spectroscopy, and thermogravimetric analysis. Among the mesoporous catalysts, 10 wt% WO _x /KIT-6 exhibited the best catalytic performance. Sulfur-containing organic compounds, such as dibenzothiophene, 4,6-dimethyldibenzothiophene, and benzothiophene, were completely (100 %) removed from the model oil over 10 wt% WO _x /KIT-6 catalyst in 2 h. In addition, the catalyst could be reused several times with only slight decrease in catalytic activity.     

Effect of γ-irradiation on conductivity of cadmium-mercury-tellurium single crystals in weak and strong electric fields

The effect of γ-radiation on electrical conductivity of Cd _x Hg_{1 ? x} Te (0.25 ≤ x ≤ 0.95) single crystals in weak and strong electric fields has been investigated. It has been shown that at relatively low fields in which charge carriers are still warm, the dependence (Δσ/σ₀) ～ E ² is observed because of the dominance of scattering on acoustic lattice vibrations with the increasing electric field strength; with a further increase in the field strength, the carriers become hot and the dependence of σ upon E becomes linear. The effect of irradiation by Γ-rays on the dependence of σ upon E in these samples is explained by a significant concentration of the intrinsic impurity centers in the crystals and their redistribution with the increasing radiation dose.     

Computational insights into allosteric interaction between benzoazepin-2-ones and lung cancer-associated PDK1: Implications for activator design

3-Phosphoinositide-dependent kinase-1 (PDK1) plays a key role in the regulation of physiological processes and its catalytic activity is tightly regulated by allosteric modulators which bind to the PDK1 Interacting Fragment (PIF) pocket. However, details on the allosteric modulators regulation of the PDK1 catalytic activity remain elusive. Here, molecular docking and molecular dynamics (MD) simulations were performed to investigate the allosteric regulation of PDK1 induced by one of the benzoazepin-2-ones, the most potent compound 17 (BAZ2O). Molecular docking and MD simulation revealed that BAZ2O was located in the PIF pocket formed by residues from β4 and β5 sheets and helices αB and αC. BAZ2O formed a hydrogen bond with Arg131 and participated in hydrophobic interactions with Ile119, Thr148, Gln150, Leu155 and Phe157. Further comparative analyses of PDK1 in its apo and BAZ2O-bound states unveiled that BAZ2O promoted the structural coupling between the important catalytic domains of PDK1, including the activation loop and the helices αB and αC, thereby stabilizing the PDK1 conformation for catalysis. Understanding the allosteric interaction of PDK1 with small molecules provides a potentially valuable possibility of designing more potent allosteric modulators with therapeutic implications for lung cancer.