Reaction mechanism of NO with hydrolysates of NAMI-A: an MD simulation by combining the QM/MM(ABEEM) with the MD-FEP method

Nitrosylation reaction mechanisms of the hydrolysates of NAMI-A and hydrolysis reactions of ruthenium nitrosyl complexes were investigated in the triplet state and the singlet state. Activation free energies were calculated by combining the QM/MM(ABEEM) method with free energy perturbation theory, and the explicit solvent environment was simulated by an ABEEMσπ polarizable force field. Our results demonstrate that nitrosylation reactions of the hydrolysates of NAMI-A occur in both the triplet and the singlet states. The Ru-N-O angle of the triplet ruthenium nitrosyl complexes is in the range of 132.0°–138.2°. However, all the ruthenium nitrosyl complexes at the singlet state show an almost linear Ru-N-O angle. The nitrosylation reaction happens prior to the hydrolysis reaction for the first-step hydrolysates. The activation free energies of the nitrosylation reactions show that the H₂O-NO exchange reaction of [RuCl₄(Im)(H₂O)] in the singlet spin sate is the most likely one. Comparing with the activation free energies of the hydrolysis reactions of the ruthenium nitrosyl complexes, the results indicate that the rate of the DMSO–H₂O exchange reaction of [RuCl₃(NO)(Im)(DMSO)] is faster than that of [RuCl₃(H₂O)(Im)(DMSO)] in both the triplet spin state and the singlet spin state. © 2018 Wiley Periodicals, Inc.     

Initial state and transition state solvation in substitution at the square-planar complexes, [PtCl4]2− and [Pd(Et4dien)Cl]+

Summary Rate constants have been determined for the reaction of [PtCl₄]^2– with cyanide in water and in 20% and 40% (v/v) methanol, and for the reaction of [Pd(Et₄dien)Cl]⁺ with thiourea in water, in 50% methanol, and in 50% DMSO, in all cases at 298.2K. The solubility of K₂PtCl₄ has been determined in water and in 20% and 40% methanol; the solubility of [Pd(Et₄dien)Cl]Cl has been determined in water, in 20%, 40%, 60%, and 80% methanol, and in 40% and 80% DMSO; again in all cases at 298.2K. From these solubilities, Gibbs free energies of transfer for the [PtCl₄]^2– and [Pd(Et₄dien)Cl]⁺ ions have been estimated. From these transfer data, published transfer data for cyanide and thiourea, and these and earlier kinetic results, solvent effects on reactivity have been dissected into their initial state and transition state components for the following four reactions: [PtCl₄]^2– hydrolysis, [PtCl₄]^2– plus cyanide, [Pd(Et₄dien)Cl]⁺ substitution, and [Pd(Et₄-dien)Cl]⁺ plus thiourea. The patterns thus established are discussed, and compared with those previously obtained for some other reactions of transition metal complexes.     

The Role of γ -Aminopropyltriethoxysilane (γ -APS) on Thermal Stability of TEOS-PDMS Ormosils

The degradation process of TEOS-PDMS Ormosils containing different amounts of γ -APS has been studied by means of DTA, TG, FTIR and ²⁹Si-NMR measurements. It has been found that the amount of γ -APS improved the thermal properties of Ormosil materials. The increase in γ -APS content causes the increment on the decomposition temperatures and activation energies of the studied Ormosils. These results have been attributed to the favourable effect of γ -APS in the copolymerisation reaction between TEOS and PDMS molecules. ²⁹Si-NMR analyses have shown that the incorporation of γ -APS increases the concentration of D(Q) units in the Ormosil structure, i.e., increases the number of TEOS molecules bonded to PDMS ones. Initial decomposition temperature (IDT), temperature of maximum weight loss rate (T_max), integral procedure decomposition temperature (IPDT) and activation energy values (E) were calculated from different equations which described the degradation of these materials. Addition of 10 wt% γ -APS produced an increase of 63^∘C in the IDT and of 115 and 110^∘C, respectively, for T_max and IPDT (up to 478 and 610^∘C) compared to the free γ -APS Ormosil. Activation energy values also rise up to 69.4 kJ⋅ mol⁻¹ by introducing 10 wt% of γ -APS.     

Thermodynamic properties of electrolyte solutions: An EMF study of the activity coefficients of KCl in the system KCl−KNO3−H2O at 25, 35 and 45°C

Electromotive force measurements were carried out on the system KCl–KNO₃–H₂O at constant total ionic strengths of 0.5, 1.0, 2.0 and 3.0 mol-kg^–1 and at 25, 35 and 45°C using a cell consisting of a potassium ionselective electrode and a Ag/AgCl electrode. The Harned coefficients and the Pitzer binary and ternary interaction parameters for the system have been evaluated at each temperature. The osmotic coefficients, excess free energies of mixing and heats of mixing of the system have been predicted at each of the experimental temperatures and ionic strengths. The solubility data at 25°C are also interpreted.     

Three-dimensional structure of 3-iminoquinuclidines

The syn — anti isomerism of some 3-iminoquinuclidines was studied by means of ¹H and ¹³C NMR spectroscopy with a paramagnetic-shift reagent [Eu(DPM)₃]. The conformations and configurations of these compounds were established, and the differences in the free energies of the isomers and the free energies of activation of the isomerization were calculated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1241–1247, September, 1978.     

Low Energy Electron Attachment by Some Chlorosilanes

In this paper, the rate coefficients (k) and activation energies (E_a) for SiCl₄, SiHCl₃, and Si(CH₃)₂(CH₂Cl)Cl molecules in the gas phase were measured using the pulsed Townsend technique. The experiment was performed in the temperature range of 298–378 K, and carbon dioxide was used as a buffer gas. The obtained k depended on temperature in accordance with the Arrhenius equation. From the fit to the experimental data points with function described by the Arrhenius equation, the activation energies (E_a) were determined. The obtained k values at 298 K are equal to (5.18 ± 0.22) × 10⁻¹⁰ cm³·s⁻¹, (3.98 ± 1.8) × 10⁻⁹ cm³·s⁻¹ and (8.46 ± 0.23) × 10⁻¹¹ cm³·s⁻¹ and E_a values were equal to 0.25 ± 0.01 eV, 0.20 ± 0.01 eV, and 0.27 ± 0.01 eV for SiHCl₃, SiCl₄, and Si(CH₃)₂(CH₂Cl)Cl, respectively. The linear relation between rate coefficients and activation energies for chlorosilanes was demonstrated. The DFT/B3LYP level coupled with the 6-31G(d) basis sets method was used for calculations of the geometry change associated with negative ion formation for simple chlorosilanes. The relationship between these changes and the polarizability of the attaching center (α_centre) was found. Additionally, the calculated adiabatic electron affinities (AEA) are related to the α_centre.     

Kinetic energy release distribution in the fragmentation of energy-selected iodopropane ions

The technique of threshold photoelectron-photoion coincidence (PEPICO) has been employed to determine the average kinetic energy release and the kinetic energy release distribution (KERD) for the iodine loss from 1- and 2-iodopropane ions as a function of the ion internal energy. The KERDs at all precursor-ion energies investigated (0–3 eV excess energy) have the shape of statistically expected distributions, 1-iodopropane ions which dissociate with an apparent 0.16 eV reverse activation barrier, are shown to isomerize at low energies prior to dissociation, to produce subsequently the 2-propyl C₃H₇^? structure. At high energies they may form a different C₃H₇^? isomer. The experimentally observed average kinetic energy releases are approximately a factor of 2 greater than expected statistically suggesting that not all vibrational modes participate in the energy disposal. The secondary dissociation of the C₃H₇^? isomers to C₃H₃ which is inhibited by a reverse activation barrier of = 0.4 eV indicates that the 1- and 2-iodopropane ions dissociate 75% and 60% respectively, to form the excited 1(²P_1/2) atoms.     

Thermodynamic and kinetic characteristics of intermediates of electrode reactions. Comparative laser photoemission study of the kinetics of electron transfer for certain alkylaryl and alkylhalide radicals

Using the laser photoemission technique, a comparative study of thermodynamic and energy characteristics of electron transfer (ET) is carried out for a number of alkylaryl intermediates (IM) (benzyl, benzhydryl radicals) and alkyl halides (chloromethyl and dichloromethyl radicals). It is found that the standard free energies of activation of radicals under study are 0.34–0.38 eV and the preexpoential factors are between 10⁹ and 10¹⁰s^?1 and weakly depend on the solution nature. The reorganization energies of the medium for these IM are estimated in terms of the classical Marcus theory. The results are compared with the literature data on the dissociative ET in monohalogenomethanes CH₃Hal/CH₃Hal^?·, polychloromethanes CH_nHal_{4 ? n} /CH_nHal _4?n ^?· , and some other systems. Possible reasons for the different probabilities of observing reversible ET for IM under study are discussed.     

Kinetics of the metal-ligand exchange of cadmium rhodo- and pyrroporphyrins with cobalt and zinc chlorides in organic solvents

Experimental data on electron absorption spectra (EASs) and the kinetics of substitution of Co²⁺ for the central Cd²⁺ ion in rhodoporphyrin complexes (CdRodP) in the reaction with CoCl₂ in acetonitrile (AN) and ZnCl₂ in dimethyl sulfoxide (DMSO) and the substitution of Zn²⁺ for Cd²⁺ in pyrroporphyrin complexes (CdPyrP) in the reaction with ZnCl₂ in DMSO are reported and discussed. The evolution of EASs in the reaction of metal-ligand exchange and the effective and true rate constants of the exchange reaction are reported. The activation energies and activation entropies are estimated.     

The interaction between n-alkyl trimethylammonium bromides with poly(l-aspartate): a thermodynamics study

Specific conductivities of a homologous series of n-alkyl trimethylammonium bromides (C₈,C₁₀,C₁₂ and C₁₄TABs) in the presence of poly(l-aspartate) in glycine buffer at pH 3.2 and 25 ^∘C have been measured over a range of C _n TAB concentrations. From the conductivity changes, the number of surfactant molecules absorbed onto the polymer, the Gibbs free energies of adsorption and the equilibrium constants have been calculated. A statistical thermodynamics analysis was used to obtain the Gibbs free energies of adsorption. The results obtained using both methods are compared and analysed. Received: 15 December 1999 Revised form: 29 February 2000 Accepted: 3 March 2000     

Formation pathways of DMSO2 in the addition channel of the OH‐initiated DMS oxidation: A theoretical study

The production of dimethyl sulfoxide (DMSO) and dimethyl sulfone (DMSO₂) in the dimethyl sulfide (DMS) degradation scheme initiated by the hydroxyl (OH) radical has been shown to be very sensitive to nitrogen oxides (NO_x) levels. In the present work we have explored the potential energy surfaces corresponding to several reaction pathways which yield DMSO₂ from the CH₃S(O)(OH)CH₃ adduct [including the formation of CH₃S(O)(OH)CH₃ from the reaction of DMSO with OH] and the reaction channels that yield DMSO or/and DMSO₂ from the CH₃S(O₂)(OH)CH₃ adduct are also studied. The formation of the CH₃S(O₂)(OH)CH₃ adduct from CH₃S(OH)CH₃ (DMS‐OH) and O₂ was analyzed in our previous work. All these pathways due to the presence of NO_x (NO and NO₂) and also due to the reactions with O₂, OH and HO₂ are compared with the objective of inferring their kinetic relevance in the laboratory experiments that measure DMSO₂ (and DMSO) formation yields. In particular, our theoretical results clearly show the existence of NO_x‐dependent pathways leading to the formation of DMSO₂, which could explain some of these experimental results in comparison with experimental measurements carried out in NO_x‐free conditions. Our results indicate that the relative importance of the addition channel in the DMS oxidation process can be dependent on the NO_x content of chamber experiments and of atmospheric conditions. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009     

S‐Trifluoromethylation of Thiols by Hypervalent Iodine Reagents: A Joint Experimental and Computational Study

The radical trifluoromethylation of thiophenol in condensed phase applying reagent 1 (3,3‐dimethyl‐1‐(trifluoromethyl)‐1λ³,2‐benziodoxol) has been examined by both theoretical and experimental methodologies. On the basis of ab initio molecular dynamics and metadynamics we show that radical reaction mechanisms favourably compete with polar ones involving the S‐centred nucleophile thiophenol, their free energies of activation, ΔF^≠, lying between 9 and 15 kcal mol^?1. We further show that the origin of the proton activating the reagent is important. Hammett plot analysis reveals intramolecular protonation of 1 , thus generating negative charge on the sulfur atom in the rate‐determining step. The formation of a CF₃ radical can be thermally induced by internal dissociative electron transfer, its activation energy, ΔF^≠, amounting to as little as 10.8 and 2.8 kcal mol^?1 for reagent 1 and its protonated form 2 , respectively. The reduction of the iodine atom by thiophenol occurs either subsequently or in a concerted fashion.     

Kinetics of the Dissolution of Silver in Thiocarbamide Solutions

The dependence of the rate of solution of silver on the pH of the solution, the ratio of the iron(III) and thiocarbamide concentrations, and the temperature has been determined. The rate constants for the solution of silver (k _i = 2.3·10^–4 to 9.6·10^–4s^–1) at temperatures from 283-298 K have been calculated and from the temperature dependence of the rate constant the activation energies have been calculated: 68.84 kJ/mol for kinetic control of the rate of solution and 26.06 kJ/mol in the adsorption inhibition region.     

The performance of ANI-ML potentials for ligand-n(H2O) interaction energies and estimation of hydration free energies from end-point MD simulations

Here, we investigate the performance of “Accurate NeurAl networK engINe for Molecular Energies” (ANI), trained on small organic compounds, on bulk systems including non-covalent interactions and applicability to estimate solvation (hydration) free energies using the interaction between the ligand and explicit solvent (water) from single-step MD simulations. The method is adopted from ANI using the Atomic Simulation Environment (ASE) and predicts the non-covalent interaction energies at the accuracy of wb97x/6-31G(d) level by a simple linear scaling for the conformations sampled by molecular dynamics (MD) simulations of ligand-n(H₂O) systems. For the first time, we test ANI potentials' abilities to reproduce solvation free energies using linear interaction energy (LIE) formulism by modifying the original LIE equation. Our results on ~250 different complexes show that the method can be accurate and have a correlation of R² = 0.88–0.89 (MAE <1.0 kcal/mol) to the experimental solvation free energies, outperforming current end-state methods. Moreover, it is competitive to other conventional free energy methods such as FEP and BAR with 15-20 × fold reduced computational cost.     

A theoretical study of electrocatalytic ammonia synthesis on single metal atom/MXene

Electrocatalytic ammonia synthesis under mild conditions is an attractive and challenging process in the earth's nitrogen cycle, which requires efficient and stable catalysts to reduce the overpotential. The N₂ activation and reduction overpotential of different Ti₃C₂O₂-supported transition metal (TM) (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Rh, Pd, Ag, Cd, and Au) single-atom catalysts have been analyzed in terms of the Gibbs free energies calculated using the density functional theory (DFT). The end-on N₂ adsorption was more energetically favorable, and the negative free energies represented good N₂ activation performance, especially in the presence Fe/Ti₃C₂O₂ (?0.75 eV). The overpotentials of Fe/Ti₃C₂O₂, Co/Ti₃C₂O₂, Ru/Ti₃C₂O₂, and Rh/Ti₃C₂O₂ were 0.92, 0.89, 1.16, and 0.84 eV, respectively. The potential required for ammonia synthesis was different for different TMs and ranged from 0.68 to 2.33 eV. Two possible potential-limiting steps may be involved in the process: (i) hydrogenation of N₂ to *NNH and (ii) hydrogenation of *NH₂ to ammonia. These catalysts can change the reaction pathway and avoid the traditional N–N bond-breaking barrier. It also simplifies the understanding of the relationship between the Gibbs free energy and overpotential, which is a significant factor in the rational designing and large-scale screening of catalysts for the electrocatalytic ammonia synthesis.     

Catalytic Conversion of Xylose to Furfural by p-Toluenesulfonic Acid (pTSA) and Chlorides: Process Optimization and Kinetic Modeling

Furfural is one of the most promising precursor chemicals with an extended range of downstream derivatives. In this work, conversion of xylose to produce furfural was performed by employing p-toluenesulfonic acid (pTSA) as a catalyst in DMSO medium at moderate temperature and atmospheric pressure. The production process was optimized based on kinetic modeling of xylose conversion to furfural alongwith simultaneous formation of humin from xylose and furfural. The synergetic effects of organic acids and Lewis acids were investigated. Results showed that the catalyst pTSA-CrCl₃·6H₂O was a promising combined catalyst due to the high furfural yield (53.10%) at a moderate temperature of 120 °C. Observed kinetic modeling illustrated that the condensation of furfural in the DMSO solvent medium actually could be neglected. The established model was found to be satisfactory and could be well applied for process simulation and optimization with adequate accuracy. The estimated values of activation energies for xylose dehydration, condensation of xylose, and furfural to humin were 81.80, 66.50, and 93.02 kJ/mol, respectively.     

Assignment of the first photoelectron band of the CH<Subscript>3</Subscript>CHCl radical using ab initio quantum mechanical calculations

HeI photoelectron spectra have been recorded for the reaction of atomic fluorine with ethyl chloride at different reaction times. A structured band associated with a short-lived primary reaction product has been recorded with adiabatic and vertical ionization energies of (7.84±0.02) and (8.18±0.02) eV respectively. An average vibrational separation of (680±30) cm^–1was observed in this band. Comparison between the experimental vertical and adiabatic ionization energies and ionization energies computed for CH₃CHCl (X²A) and CH₂CH₂Cl (X²A) at different levels of theory led to the assignment of the observed first photoelectron band to the ionization of CH₃CHCl (X²A). The observed vibrational structure was assigned to excitation of the C–Cl stretching mode in CH₃CHCl⁺(X¹A).Proceedings of the 11th International Congress of Quantum Chemistry satellite meeting in honor of Jean-Louis Rivail     

Excess partial molar enthalpies,entropies, Gibbs energies,and volumes in aqueous dimethylsulfoxide

The excess partial molar enthalpies, the vapor pressures, and the densities of dimethylsulfoxide (DMSO)–H₂O mixtures were measured and the excess partial molar Gibbs energies and the partial molar volumes were calculated for DMSO and for H₂O. The values of the excess partial molar Gibbs energies for both DMSO and H₂O are negative over the entire composition range. The results for the water-rich region indicated that the presence of DMSO enhances the hydrogen bond network of H₂O. Unlike monohydric alcohols, however, the solute-solute interaction is repulsive in terms of the Gibbs energy. This was a result of the fact that the repulsion among solutes in terms of enthalpy surpassed the attraction in terms of entropy. The data in the DMSO-rich region suggest that DMSO molecules form clusters which protect H₂O molecules from exposure to the nonpolar alkyl groups of DMSO.     

Effects of substituent groups of polyimides on sorption and diffusion of gases

Sorption rate curves of CO₂, N₂, and He gases below 1 atm were measured for polyimide films prepared from benzophenone tetracarboxylic dianhydride (BTDA) with 3,5-diaminotoluene trifluoride (DATF), 2,4-diaminotoluene (DAT), m-phenylenediamine (MPD), and diaminobenzoic acid (DABA). The molecular structures of these four polyimides differ only in the substituent groups of the diamine structure. These polyimides exhibit dualmode type sorption isotherms for carbon dioxide that are concave to the pressure axis, typical of glassy polymer/gas system. The apparent diffusion coefficients below 1 atm pressure of carbon dioxide for this series of compounds decrease in the order: BTDA-DATF > BTDA-DAT > BTDA-MPD > BTDA-DABA. A linear relation between the logarithm of the apparent diffusion coefficient and the reciprocal of free volume, calculated by the method of Bondi using density data, is found for these polyimides. However, this tendency is not observed for the other two gases. The activation energies of the apparent diffusion coefficients at 20 cmHg pressure of carbon dioxide increase with increasing cohesive energy density of the polyimides. The energy per mole of free volume elements in a liquidlike structure in each cohesive energy density may be equated to the activation energy and used to calculate the free volume. The values from the activation energy are almost the same as those from Bondi's method.