Theoretical study of solvent effects on the structures and isomerization of silylenoid H<Subscript>2</Subscript>SiLiF

The structures and isomerization of silylenoid H₂SiLiF are investigated by density functional theory (DFT) at B3LYP/6-311+G(d,p) level. The solvent effects are modeled using the self-consistent reaction field (SCRF) method with Tomasi’s polarized continuum model (PCM). Five representative solvents, i.e. benzene, ether, THF, acetone, and DMSO, are chosen for this work. Special attention is paid to THF solvent. The results indicate that the polarity of solvents has played an important role on the structures and relative stabilities of different isomers. Contrary to the three-membered ring structure 1, the relative stability of the “classical” tetrahedron structure 4 increases with increasing dielectric constants (ε) of solvents. The σ-complex isomer 3 is most unstable structure. Although the relative energies are reduced with increasing dielectric constants (ε) of solvents, the p-complex structure 2 still has the lowest energy. The effects of solvents on the dipole moments and charge distributions are also discussed.     

A theoretical study of the solvent effect on the interaction of C<Subscript>20</Subscript> and N<Subscript>2</Subscript>H<Subscript>2</Subscript>

In this work, the interaction of C₂₀ and the N₂H₂ fragment is investigated at the M062X/6-311G(d,p) level of theory in both gas and solution phases. The interaction energies obtained by the standard method are corrected by the basis set superposition error (BSSE) during the geometry optimization for all molecules at the same levels of theory. The results obtained from these calculations reveal that the interaction between C₂₀ and N₂H₂ increases in the presence of more polar solvents. Values of the electrophilic charge transfer show the charge flow from C₂₀ to N₂H₂. The influence of the solvent on the hyperpolarizability indicates that β_tot values decrease on passing from vacuum to the solution phase.     

Hydrogen generation from H<Subscript>2</Subscript>O/H<Subscript>2</Subscript>O<Subscript>2</Subscript>/MnWO<Subscript>4</Subscript> system

Hydrogen gas as a clear energy resource was found to be largely bubbled from a H₂O/H₂O₂/MnWO₄ system. MnWO₄ powder was fabricated by an aqueous reaction method. The powder was characterized with X-ray diffraction (XRD), transmission electron microscope (TEM), and X-ray photoelectron spectrometry (XPS). The efficiency of the hydrogen generation increases with an increase in initial pH in the appropriate range, H₂O₂ proportion, MnWO₄ proportion, and intensity of light resource. Calcining at 400 °C for 1 h can make the MnWO₄ powder synthesized by an aqueous reaction more effective for H₂ generation and more stable in higher initial pH. The MnWO₄ catalyst shows a long-term stability for photocatalytic H₂ generation. A mechanism was suggested for the hydrogen generation from the H₂O/H₂O₂/MnWO₄ system together with XPS analysis.     

X-ray photoelectron study of the interaction of H<Subscript>2</Subscript> and H<Subscript>2</Subscript>+O<Subscript>2</Subscript> mixtures on the Pt/MoO<Subscript>3</Subscript> model catalyst

The effects of H₂ and H₂ + O₂ gas mixtures of varying composition on the state of the surface of the Pt/MoO₃ model catalyst prepared by vacuum deposition of platinum on oxidized molybdenum foil were investigated by X-ray photoelectron spectroscopy (XPS) at room temperature and a pressure of 5–150 Torr. For samples with a large Pt/Mo ratio, the XP spectrum of large platinum particles showed that the effect of hydrogen-containing mixtures on the catalyst was accompanied by the reduction of molybdenum oxide. This effect results from the activation of molecular hydrogen due to the dissociation on platinum particles and subsequent spill-over of hydrogen atoms on the support. The effect was not observed at low platinum contents in the model catalyst (i.e., for small Pt particles). It is assumed for the catalyst that the loss of its hydrogen-activating ability is a consequence of the formation of platinum hydride. Possible participation of platinum hydride as intermediate in hydrogen oxidation to H₂O₂ is discussed.     

The effect of curvature of Li-doped polycyclic hydrocarbon on its interaction energy with H<Subscript>2</Subscript> and H<Subscript>2</Subscript>O: DF-SAPT (DFT) calculation

In this work, the interaction of three Li⁺-doped polycyclic hydrocarbons (Li⁺-DPH) with H₂ and H₂O was calculated to investigate the effect of curvature of substrate on the interaction energy (E_int). For this purpose, the E_int and its decomposed energy components (electrostatic (E_elec), exchange (E_exch), induction (E_ind), and dispersion energy (E_disp)) were calculated using DF-SAPT (DFT) methodology for the selected systems (Li⁺-(3,3) carbon nanotube (Li⁺-CNT33), Li⁺-(6,6) carbon nanotube (Li⁺-CNT66), and Li⁺-graphene). According to the results, E_int does not change significantly with curvature for the interaction between both H₂ and H₂O gases and the selected Li⁺-DPH. Since the variation of the E_int with the curvature of Li⁺-DPH is not significant, the selection of a planar Li⁺-DPH is a trustworthy model to develop a general force field for describing the interaction between a Li⁺-DPH and adsorbed gases. The results reveal that, in the case of the H₂, the components E_elect, E_exch, E_ind, and E_disp have shown a decreasing trend with Li⁺-DPH’s curvature decrement. However, for the H₂O, E_elect, E_exch, and E_ind decrease from the Li⁺-CNT33 to the Li⁺-CNT66 while they increase from the Li⁺-CNT66 to the Li⁺-graphene. In this case, the E_disp increases with a decrease of the curvature of Li⁺-DPH. Finally, it can be seen that although the variation of the E_int with the curvature of Li⁺-DPH is not significant, the variation trend of the interaction energy components and the amount of variation depend on the gas molecule and in some cases are not negligible.     

Study on chemisorption of H<Subscript>2</Subscript>, O<Subscript>2</Subscript>, CO and C<Subscript>2</Subscript>H<Subscript>4</Subscript>on Pt-Ag/SiO<Subscript>2</Subscript>catalysts by microcalorimetry and FTIR

Adsorption microcalorimetry has been employed to study the interaction of ethylene with the reduced and oxidized Pt-Ag/SiO₂catalysts with different Ag contents to elucidate the modified effect of Ag towards the hydrocarbon processing on platinum catalysts. In addition, microcalorimetric adsorption of H₂, O₂, CO and FTIR of CO adsorption were conducted to investigate the influence of Ag on the surface structure of Pt catalyst. It is found from the microcalorimetric results of H₂and O₂adsorption that the addition of Ag to Pt/SiO₂leads to the enrichment of Ag on the catalyst surface which decreases the size of Pt surface ensembles of Pt-Ag/SiO₂catalysts. The microcalorimetry and FTIR of CO adsorption indicates that there still exist sites for linear and bridged CO adsorption on the surface of platinum catalysts simultaneously although Ag was incorporated into Pt/SiO₂. The ethylene microcalorimetric results show that the decrease of ensemble size of Pt surface sites suppresses the formation of dissociative species (ethylidyne) upon the chemisorption of C₂H₄on Pt-Ag/SiO₂. The differential heat vs. uptake plots for C₂H₄adsorption on the oxygen-preadsorbed Pt/SiO₂and Pt-Ag/SiO₂catalysts suggest that the incorporation of Ag to Pt/SiO₂could decrease the ability for the oxidation of C₂H₄.     

Substituent and solvent effects on geometric and electronic structure of C<Subscript>5</Subscript>H<Subscript>5</Subscript>Ir(PH<Subscript>3</Subscript>)<Subscript>3</Subscript> iridabenzene: A theoretical insight

Using MPW1PW91 quantum chemical calculations, we report structures, frontier orbital analysis, natural bond analysis, and aromaticity of the C₅H₅Ir(PH₃)₃ iridabenzene and XC₅H₄Ir(PH₃)₃ para-substituted iridabenzenes. The substituent effects were estimated from the donor–acceptor interaction energies of the natural bond orbitals of substituent and iridabenzene frame. Nucleus-independent chemical shift (NICS) has been evaluated to understand the aromaticity. Time dependent density functional theory (TD-DFT) is used to calculate the energy, oscillatory strength and wavelength absorption maxima (λ_max) of electronic transitions and their nature. Changes in hyperpolarizability of molecules are studied. Influence of solvent on the structure, frontier orbital energies, λ_max, and hyperpolarizability of C₅H₅Ir(PH₃)₃ iridabenzene has been studied.     

Synthesis and characterization of a new monophosphate (C<Subscript>6</Subscript>H<Subscript>16</Subscript>N<Subscript>2</Subscript>)(H<Subscript>2</Subscript>PO<Subscript>4</Subscript>)<Subscript>2</Subscript>

Chemical preparation, crystal structure, and NMR spectroscopy of a new trans-2,5-dimethylpiperazinium monophosphate are given. This new compound crystallizes in the triclinic system, with the space group P-1 and the following parameters: a = 6.5033(3), b = 7.6942(4), c = 8.1473(5) Å, α = 114.997(3), β = 92.341(3), γ = 113.136(3), V = 329.14(3) ų, Z = 1, and D_x = 1.565 g cm^?3. The crystal structure has been determined and refined to R = 0.030 and R _w(F ²) = 0.032 using 1558 independent reflections. The structure can be described as infinite [H₂PO₄] _n ^n? chains with (C₆H₁₆N₂)²⁺ organic cations anchored between adjacent polyanions to form columns of anions and cations running along the b axis. This compound has also been investigated by IR, thermal, and solid-state, ¹³C and ³¹P MAS NMR spectroscopies and Ab initio calculations.     

A review on nanomaterial-based electrochemical sensors for H<Subscript>2</Subscript>O<Subscript>2</Subscript>, H<Subscript>2</Subscript>S and NO inside cells or released by cells

The incorporation of nanomaterials into electrochemical sensors is an attractive approach towards the improvement of the sensitivity of amperometry and also can provide improved sensor selectivity and stability. This review (with 137 references) details the current state of the art and new trends in nanomaterial-based electrochemical sensing of hydrogen peroxide (H₂O₂), hydrogen sulfide (H₂S) and nitric oxide (NO) in cells or released by cells. The article starts with a discussion of the significance of the three analytes, and this is followed by three sections that summarize the electrochemical detection schemes for H₂O₂, H₂S and NO. Each section first summarizes the respective physiological roles, and then reviews electrochemical sensors based on the use of carbon nanomaterials, noble metal nanomaterials, metal oxide nanomaterials, and layered doubled hydroxides. The materials are compiled in three tables along with figures of merit for the various sensors.

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Graphical abstract Nanomaterial-based electrochemical sensors for Reactive oxygen species (H₂O₂), Reactive nitrogen species (NO) and Reactive hydrogen sulfide species (H₂S) inside cells or released by cells.

     

Quantum chemical study of H<Subscript>2</Subscript> adsorption on Pd<Subscript>21</Subscript> cluster

Modeling of the interaction of an H₂ molecule with the surface of the Pd₂₁ cluster in different spin states was performed using the DFT/PBE scalar relativistic approximation. The spin multiplicity of the system significantly affects the mechanism of adsorption, its parameters, and migration of hydrogen atoms. The H atoms can migrate over the cluster surface with low barriers (1.6 kcal mol^–1). The complex with C _2v symmetry, wherein the H atoms occupy adjacent fcc sites, is the most energetically stable.     

Structure and some properties of [UO<Subscript>2</Subscript>(SeO<Subscript>4</Subscript>)(C<Subscript>5</Subscript>H<Subscript>12</Subscript>N<Subscript>2</Subscript>O)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)]

The complex [UO₂(SeO₄)(C₅H₁₂N₂O)₂(H₂O)] (I) was synthesized and studied by thermal analysis, IR spectroscopy, and X-ray crystallography. The crystals are orthorhombic: a = 13.1661(3) Å, b = 16.4420(5) Å, c = 17.4548(6) Å, Pbca, Z = 8, R = 0.0423. The structural units of crystal I are chains with the composition coinciding with that of the compounds of the AB₂M ₃ ¹ crystal chemical group of the uranyl complexes (A = UO ₂ ²⁺ , B² = SeO ₄ ^2? , M¹ = C₅H₁₂N₂O and H₂O).     

Steric effects on the singlet-triplet energy gaps of five-membered ring R<Subscript>2</Subscript>C<Subscript>4</Subscript>H<Subscript>2</Subscript>M

Thermal internal energy gaps, ΔE _s−t; enthalpy gaps, ΔH _s−t; Gibbs free energy gaps, ΔD _s−t, between singlet (s) and triplet (t) states of R₂C₄H₂M (M = C, Si, and Ge) were calculated at B3LYP/6-311++G** level of theory. The ΔG _s−t of R₂C₄H₂C was increased in the order (in kcal/mol): R = −CH₃ (−10.51) > −H (−9.59) > i-Pr (−9.51) > t-Bu (−8.98). While, the ΔG _s−t of R₂C₄H₂Si and R₂C₄H₂Ge were increased in the order (in kcal/mol): −CH₃ (17.01) > i-Pr (15.30) > −H (15.26) > t-Bu (14.35) and -H (22.79) > −CH₃ (22.69) > i-Pr (21.66) > t-Bu (21.01), respectively.     

Study on the cluster of floating dross before nucleating during hot-dipping process

At present, hot-dipping anticorrosion metalliccoating on the surface of steel base is the main methodto prevent atmospheric corrosion of steel. With thechange of atmospheric environment, the traditionalidea of hot-dipping pure Zn cladding already does not…     

The stability and structure of (N<Subscript>2</Subscript>)<Subscript>j</Subscript>(H<Subscript>2</Subscript>O)<Subscript>i</Subscript> and (Ar)<Subscript>j</Subscript>(H<Subscript>2</Subscript>O)<Subscript>i</Subscript> clusters

The stability and structure of water clusters absorbing nitrogen molecules or argon atoms was analyzed by molecular dynamics simulation at 233 K. The (?μ/?i)_{V, T} derivative of the chemical potential, a value characterizing the stability of a cluster with respect to its size, depends linearly on the number of molecules i. According to this criterion, the clusters under study become stable near i = 40. The average length of H-bonds increases monotonically in the growing cluster of pure water and exhibits oscillatory behavior if the growing cluster contains N₂ molecules or Ar atoms. The number of H-bonds per molecule oscillates between one and six as the cluster size changes. These oscillations are damped in pure water and sustained for clusters containing impurities, especially argon.     

Efficient and convenient oxidation of cyclohexene to adipic acid with H<Subscript>2</Subscript>O<Subscript>2</Subscript> catalyzed by H<Subscript>2</Subscript>WO<Subscript>4</Subscript> in acidic ionic liquids

A simple, efficient, and eco-friendly catalytic system for the oxidation of cyclohexene to adipic acid with H₂O₂ catalyzed by H₂WO₄ in Brønsted acidic ionic liquids under solvent-free conditions has been developed. Reaction conditions such as the catalysts, the types of anions and cations for Brønsted acidic ionic liquids, reaction temperature, and the amount of hydrogen peroxide, were investigated. Moreover, the Hammett acidity functions (H ₀) of Brønsted acidic ionic liquids were determined using UV–visible spectrophotometry. The optimum reaction condition identified was n(H₂WO₄):n(Brønsted acidic ionic liquids):n(cyclohexene):n(H₂O₂) = 0.02:0.02:1:4.4, and the yield of adipic acid was 96% under the reaction scale of 10 mmol. The catalytic system can be easily recovered and reused for four reaction runs without significant loss of catalytic activity. Simple operation of the catalyst system and avoidance of the emission of nitrous oxide are the benefits of this work.     

Thermokinetics on the reaction of formation of Dy[(C<Subscript>5</Subscript>H<Subscript>8</Subscript>NS<Subscript>2</Subscript>)<Subscript>3</Subscript>(C<Subscript>12</Subscript>H<Subscript>8</Subscript>N<Subscript>2</Subscript>)]

The enthalpy change of formation of the reaction of hydrous dysprosium chloride with ammonium pyrrolidinedithiocarbamate (APDC) and 1,10-phenanthroline (o-phen?H₂O) in absolute ethanol at 298.15 K has been determined as (-16.12 ± 0.05) kJ?mol^-1 by a microcalormeter. Thermodynamic parameters (the activation enthalpy, the activation entropy and the activation free energy), rate constant and kinetics parameters (the apparent activation energy, the pre-exponential constant and the reaction order) of the reaction have also been calculated. The enthalpy change of the solid-phase reaction at 298.15 K has been obtained as (53.59 ± 0.29) kJ?mol^t-1 by a thermochemistry cycle. The values of the enthalpy change of formation both in liquid-phase and solid-phase reaction indicated that the complex could only be synthesized in liquid-phase reaction.     

The insertion and H<Subscript>2</Subscript> elimination reactions of H<Subscript>2</Subscript>GeFMgF germylenoid with RH (R = Cl,SH, PH<Subscript>2</Subscript>)

In present paper, the insertion and H₂ elimination reactions of H₂GeFMgF germylenoid with RH (R = Cl, SH, PH₂) were investigated by means of B3LYP and QCISD calculation methods. One transition state and one intermediate were found along the potential energy surface in each insertion reaction, while for the H₂ elimination reactions, only one transition state was found between the reactants and products in each reaction process. Both for the insertion and H₂ elimination reactions, RH reactivity increases in the following order: H–Cl > H–SH > H–PH₂. The insertion and H₂ elimination reactions were compared, and the results demonstrated that the H₂ elimination should be more favorable than the corresponding insertion. The solvent effects on these two types of reactions were considered. The calculated results indicated that the solvents could accelerate the reactions by reducing their barrier heights.     

Model of the catalytic reaction 2H<Subscript>2</Subscript> + O<Subscript>2</Subscript> → H<Subscript>2</Subscript>O with the participation of molecules in a precursor state

The absence of experimental evidence for the occurrence of the catalytic reaction 2H₂ + O₂ → 2H₂O on platinum in accordance with the Langmuir-Hinshelwood mechanism was established. It was found that the heterogeneous process can be described more adequately and its nature can be better understood with consideration for chemical transformations involving molecules in a precursor state in a model of the above reaction. The inverse kinetic problem was solved. It was found that the model in which an unambiguously specified set of rate constants for the elementary steps of the reaction was used provided an opportunity to describe experimental data obtained by various authors concerning the oxidation of hydrogen on platinum over the detonating gas pressure range 10^?3-10⁵ Pa. The signs of the occurrence of heterogeneous reactions by an adsorption mechanism were found.     

PdCl<Subscript>2</Subscript>/DABCO-catalyzed direct arylation of 2-hydroxybenzaldehydes in H<Subscript>2</Subscript>O

In this paper the successful application of DABCO both as base and as ligand for efficient coupling reactions of aryl iodides and bromides with 2-hydroxybenzaldehydes in the presence of catalytic amounts of PdCl₂ in water as solvent was introduced.     

Adsorption of NO,NH<Subscript>3</Subscript> and H<Subscript>2</Subscript>O on V<Subscript>2</Subscript>O<Subscript>5</Subscript>/TiO<Subscript>2</Subscript> catalysts

The adsorption of small molecules NO, NH₃ and H₂O on V₂O₅/TiO₂ catalysts is studied with the semiempirical SCF MO method MSINDO as pre-stage for the selective catalytic reduction of NO. The mixed catalyst is represented by hydrogen-terminated cluster models. The local arrangement of the cluster atoms is in accordance with available experimental information. Partial relaxation of cluster atoms near the adsorption sites is taken into account. Calculated adsorption energies are compared with experimental literature data. Rapid convergence of computed properties with cluster size is observed. A possible reaction mechanism for the catalytic reduction of NO with NH₃ and O₂ is outlined.