A theoretical study on the dynamics of the gas phase reaction of NH<Subscript>2</Subscript>(<Superscript>2</Superscript>B<Subscript>1</Subscript>) with HO<Subscript>2</Subscript>(<Superscript>2</Superscript>A″)

Quasi-classical trajectory calculations and stochastic one-dimensional chemical master equation simulation methods are used to study the dynamics of the reaction of amidogen radical [NH₂(²B₁)] with hydroperoxyl radical [HO₂(²A″)] on the lowest singlet electronic state. The title complex reaction takes place on a multi-well multichannel potential energy surface consisting of three deep potential wells and one van der Waals complex. In quasi-classical trajectory calculations a new analytical potential energy surface based on CCSD(T)/aug-cc-pVTZ//MPW1K/6-31+G(d,p) ab initio method was driven and used to study the dynamics of the title reaction. In quasi-classical trajectory calculations, the reactive cross sections and reaction probabilities are determined for 200–2000 K relative translational energies to calculate the rate constants. The same ab initio method was used to have the necessary data for solving the one-dimensional chemical master equation to calculate the rate constants of different channels. In solving the master equation, the Lennard-Jones potential model was used to form the collision between the collider gases. The fractional populations of different intermediates and products in the early stages of the reaction were examined to determine the role of the energized intermediates and the van der Waals complex on the dynamics of the title reaction. Although the calculated total rate constants from both methods are in good agreement with the reported experimental values in the literature, the quasi-classical trajectory simulation predicts the formation of NH₂O + OH as the major channel in the title reaction in accordance with the previous studies (Sumathi and Peyerimhoff, Chem. Phys. Lett., 263:742–748, 1996), while the stochastic master equation simulation predicts the formation of HNO + H₂O as the major products.     

Rate and Equilibrium Constants for Reactions Transferring a Dimethylcarbamoyl Group between Pyridines

We have studied 18 reactions, including four identity reactions, involving transfer of a dimethylcarbamoyl group with N-acylpyridinium bonds to pyridine and its 4-substituted derivatives in acetonitrile solutions at 298 K. The rate constants k _ij varied within the range 0.4 to 10^–6 L/mol·s; the equilibrium constants K _ij varied from 10⁷ to 10^–5. The rate and equilibrium for exchange of carbamoyl groups are described satisfactorily by the Brönsted equation. We have shown that all the reactions occur according to a forced concerted S _N2 mechanism. The structure of the transition state and its position on the reaction coordinate for identity transfer are considered using a More O'Ferrall-Jencks diagram.     

Rate and Equilibrium Constants of Benzoyl Group Transfer between Pyridine N-Oxides

Kinetic characteristics of 19 transfer reactions of benzoyl group from N-benzoyloxypyridinium salts to pyridine N-oxides and 4-dimethylaminopyridine were studied in acetonitrile by the stopped-flow method. The rate of an identical reaction for 4-methoxypyridine was measured by dynamic NMR spectroscopy. For 5 other identical reactions the rates were estimated from Bronsted correlations. Equilibrium constants were estimated with the use of UV spectrophotometry (6), IR spectroscopy (2), from kinetic data (K _ij = k _ij /k _ji ) (2), and in one case as logK _i−j = logK _i−x − logK _j−x . The second order rate constants (k _ij ) varied in the range 10²–10⁵ l mol⁻¹ s⁻¹, the equilibrium constants (K _ij ) in the range 10²–10⁻²; the activation parameters (ΔH ^≠) were within 15–50 kJ mol⁻¹, (−ΔS ^≠) −20–110 J mol⁻¹ K⁻¹. The reactions under study occur in a single stage following the concerted S_N2 mechanism through an early associative transition state. The benzoyl groups exchange rate and equilibrium are well described by simplified Marcus equation (omitting the quadratic term).__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 5, 2005, pp. 788–792.Original Russian Text Copyright © 2005 by Rybachenko, Schroeder, Chotii, Lenska, Red’ko, Kovalenko.     

A kinetics study of ligand substitution reaction on dinuclear platinum complexes: Stochastic versus deterministic approach

The kinetics on a basic ligand substitution reaction on dinuclear platinum complexes [Pt(PEt₃)₂PhPt(PEt₃)₂]²⁺ and [Pt(PEt₃)₂PhCOPhPt(PEt₃)₂]²⁺ , with the ligands pyridine and 3-chloropyridine, is studied. This is a fundamental step in a self-assembly, and the time evolution has been observed with a new experimental technique, QASAP (quantitative analysis of self-assembly process), which is recently developed by Hiraoka's group. As a result of numerical calculations based on master equation, we succeed in specifying the reaction rate constants with a simple reaction model. In addition, the time evolutions of all the intermediate components produced and consumed in chemical reaction are revealed, including those unobserved in the experiments. The convergence behavior of the existence ratios of specific chemical species calculated with the stochastic algorithm method is compared with those obtained from deterministic formalism based on rate equations, revealing a clear dependence on the number of constituent molecules. © 2018 Wiley Periodicals, Inc.     

Photochemical properties of carotenoids: what can we get from the VB model?

Photo-isomerization and anti-oxidation of carotenoids have been studied for many years be-cause of their diverse roles in photobiology, photochemistry and photomedicine[1—6]. The experi-mental works revealed that the changes in the geometry between S0 (the ground state) and T1 (the first triplet state) states are very important for the two processes. Meanwhile, theoretical studies have also been carried out to investigate these processes. The polyenes have usually been used as the models for…     

Solution structure and Kirkwood-Buff theory: Informativity and sensitivity to specific interactions

A comparative significance of the contribution from density and excess Gibbs energy into Kirkwood-Buff integrals G _ij has been considered exemplified by H₂O-sulfolane, H₂O-THF and model mixtures. It is shown that some salient features of the volume properties which are generally thought to be the sign of strongly hydrophobic behavior of solutes, do not clearly manifest themselves in the concentration dependences of these integrals. Literature data for G _ij have been analyzed and the structural information inherent to G _ij is assessed. Contributions from the first and the following solvation spheres to G _ij have been evaluated from the distribution functions of model mixtures computed by the Born-Green equation and it is shown that with no new chemical bonds, the contribution from the first solvation sphere does not govern the whole of G _ij and, consequently, G _ij as calculated from the thermodynamic properties contain no direct information as far as the details of short-range interactions are concerned.     

The effect of glucose on bovine serum albumin denatured aggregation kinetics at high concentration

The effect of glucose (0–15 mass%) on the kinetics of bovine serum albumin (BSA) denatured aggregation at high concentration in aqueous solution has been studied by differential scanning calorimetry. The observed denatured aggregation process was irreversible and could be characterized by a denaturation temperature (T _m), apparent activation energy (E _a), the approximate order of reaction, and pre-exponential factor (A). As the glucose concentration increased from 0 to 15 mass%, T _m increased, E _a also increased from 514.59409±6.61489 to 548.48611±7.81302 kJ mol⁻¹, and A/s⁻¹ increased from 1.24239E79 to 5.59975E83. The stabilization increased with an increasing concentration of glucose, which was attributed to its ability to alter protein denatured aggregation kinetics. The kinetic analysis was carried out using a composite procedure involving the iso-conversional method and the master plots method. The iso-conversional method indicated that denatured aggregation of BSA in the presence and absence of glucose should conform to single reaction model. The master plots method suggested that the simple order reaction model best describe the process. This study shows the combination of iso-conversional method and the master plots method can be used to quantitatively model the denatured aggregation mechanism of the BSA in the presence and absence of glucose.     

Intradiffusion coefficients in perchloric acid solutions: Water at 5°C; water and perchlorate ion at 25°C

Intradiffusion coefficients for tritiated water (³HHO) and perchlorate ion (³⁶ClO ₄ ^- ) were measured in perchloric acid solutions. At 5°C the diffusion coefficient measured for the tritiated species increases to a maximum near 1.3 mol-dm^–3. The data at 25°C have been used to calculate distinct diffusion coefficients, D _ij ^d . As a precursor for those calculations, new estimates were made of the Onsager phenomenological coefficients, l _ij . The l _ij and D _ij ^d are similar to the respective coefficients in hydrochloric acid solutions.     

Thermal reaction of HNCO with NO2 at moderate temperatures

The thermal reaction of HNCO with NO₂ has been studied in the temperature range of 623 to 773 K by FTIR spectrometry. Major products measured are CO₂ and NO with a small amount of N₂O. Kinetic modeling of the time resolved concentration profiles of the reactants and products, aided by the thermochemical data of various likely reactive intermediates computed by means of the BAC-MP4 method, allows us to conclude that the reaction is initiated exclusively by a new bimolecular process: with a rate constant, k₁ = 2.5 × 10¹²e^?13,100/T cm³/mols. The well-known bimolecular reaction is the only strong competitive process in this important reactive system throughout the temperature range studied. Kinetic modeling of NO formation and NO₂ decay rates gave rise to values of k₁₀ which were in close agreement with literature data. © 1993 John Wiley & Sons, Inc.     

The gas-phase pyrolysis of alkyl nitrites VI. t-Amyl nitrite

The rate of decomposition of tert-amyl nitrite (t-AmONO) has been studied in the absence (120°–155°C) and presence (160°–190°C) of nitric oxide. In the absence of nitric oxide for low concentrations of tert-amyl nitrite (～10^?4M) and small extents of reaction (～1%), the first-order homogeneous rates of acetone formation are a direct measure of reaction (1) since k_3a ? k₂(NO): The rate of acetone formation is unaffected by the addition of large amounts of carbon tetrafluoride or isobutane (～1 atm) but is completely suppressed by large amounts of nitric oxide (1 atm 120°–155°C). The rate of reaction (1) is given by k₁ = 10^16.3±0.1 10^?40.3±0.1/θ sec^?1. Since (E₁ + RT) and ΔH°₁ are identical, both may be equated with D(t-AmO – NO) = 40.9 ± 0.1 kcal/mol and E₂ = 0 ± 0.1 kcal/mol. The thermochemistry leads to the result that ΔH°_f (t-AmO) = ?26.6 ± 1 kcal/mol. From ΔS°₁ and A₁, k₂ is calculated to be 10^10.5±^0.2 M^?1·sec^?1. Although the addition of nitric oxide completely suppresses acetone formation at lower temperatures, it reappears at higher temperatures. This is a result of reaction (3a) now competing with reaction (2), thus allowing k_3a to be determined. The rate constant for reaction (3a) is given by k_3a = 10^{14.7 ± 0.2} 10^{?14.3 ± 1}/θ sec^?1. There are two possible routes for the decomposition of the tert-amyloxyl radical: The dominating process is (3a). From the result at 160°C that k_3a/k_3b = 80, we arrive at the result k_3b = 10^15.0–18.7/θ sec^?1. In addition to the products accounted for by the radical split (1), methyl-2-but-1-ene and methyl-2-but-2-ene are produced as a result of the six-centre elimination of nitrous acid (5): The ratio k_5a/k_5b was 0.35. Unlike tert-butyl where the rates of the two paths were comparable [(l) and (5)], here the total rate of the elimination process was only 0.5% that of the radical split (1). The reason for this is not clear.     

Homogeneous Fermi liquid with ‘artificial’ repulsive inverse square law interparticle potential energy

A good deal is known by now on the so-called jellium model of the homogeneous electron liquid. However, much of the quantitative progress at experimentally realizable densities has come from quantal computer simulation. Therefore, we here consider a homogeneous Fermion liquid with ‘artificial’ repulsive interaction λ/(r_ij )² between Fermions i and j at separation r_ij . We discuss first of all the way the static structure function S(q), essentially the Fourier transform of the pair correlation function, is changed because of non-zero λ from the ‘Fermi hole’ form due entirely to Pauli principle effects between parallel spin Fermions. Unlike jellium with e ²/r_ij repulsive interactions, S(q) is proportional to q at long wavelengths, whereas the plasmon in jellium annulls the q term and S(q) is quadratic in q as q tends to zero. However for λ/(r_ij )² interactions, the coefficient of q appearing in the Fermi hole structure factor, is renormalized by particle repulsions. Then some discussion is given of Fermion quasiparticle lifetimes τ as the Fermi surface is approached. Arguments are presented that τ^?1 is proportional to |E???E _F| as E tends to the Fermi energy. This is already interesting, in fact, in connection with the jellium model and therefore an approximate analytic form of τ is finally derived.     

A method for selection and use of numerical integration points for molecules with cylindrical symmetry

Boys and Handy [1] have discussed the solution of the bivariational equations with restricted numerical integration. One of the weaknesses of the method was that in the numerical summations over points, some points arose with r _ij= 0 and non-zero weights. This makes the method quite impractical for the Schrodinger Hamiltonian (because of the singularity at r _ij= 0), and it cannot be advantageous for the transcorrelated Hamiltonian C^–1HC because there will be some discontinuous higher derivatives at r _ij=0. Here it is shown how the symmetry of cylindrically symmetric molecules can be used to eliminate such points, without losing any of the advantages of the overall method, such as the convergence of the eigensolutions. It is also shown how the primary numerical integration points (z _i, r_i) may be chosen in any calculation such that each is associated with an equal amount of one-electron density. The choice of the angular coordinates are governed by the removal of the r _ij=0 points and maintaining the natural orthogonality between orbitals of different symmetry types. The method has been programmed and found to be practical, although no new molecular calculations have yet been performed. It is to be hoped that these points will give a basis for new transcorrelated calculations on diatomic molecules.This paper was presented during the session on numerical integration methods for molecules of the 1970 Quantum Theory Conference in Nottingham. It has been revised in the light of the interesting discussion which followed.     

H2 formation in the reaction of O(1D) with CH4

The reaction of O(¹D) with CH₄ was studied to determine the efficiency of H₂ production in a direct process, and it was found to be 0.11 ± 0.02. Thus the two channels which account for all of the reaction between O(¹D) and CH₄ in the gas phase are      

Residence times in kink sites and Markov chain model of alloy and intermetallic compound deposition

The concept of the residence time τ_ksp of an atom in a kink site has recently been suggested to understand the processes in electrochemical deposition of alloys and intermetallic compounds. Different kink sites with different residence times must be defined for alloys and intermetallic compounds. Based on this model, the finite Markov chain theory is applied to describe the selectivity of the growth process. An analytical relationship between the alloy composition and the metal ion concentrations in the electrolyte is derived. General model parameters are ratios g _i = K _ii/K _ij of equilibrium constants of the reaction of electrolyte ions with different kink sites on the surface (i, j representing different alloy components). These ratios are called selectivity constants. For simple conditions, the equation g _i ≈ τ_ii/τ_ij connects the g _i values with the residence times. The theory is tested in the deposition of alloys Co-Ni (anomalous co-deposition) and Ni-Mo (induced co-deposition). Additionally, Bi₂Te₃, an example of stoichiometric semiconductor deposition, is treated. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 10, pp. 1216–1223. The text was submitted by the authors in English.     

Model calculations for Setchenow coefficients

The calculations of Setchenow coefficients reported earlier [H. L. Friedman, C. V. Krishnan, and C. Jolicoeur,Ann. N.Y. Acad. Sci. 204, 79 (1973)] have been extended to aqueous solutions of various nonelectrolytes mixed with alkali or alkylammonium halides. A few data for Setchenow coefficients in methanol have also been treated. The GurneyA _ij parameters for nonelectrolyte-ion interactions in models which fit the data are mostly negative, and more so the larger the solute molecules. A value ofA _ij near-100 cal-mole^–1 seems to characterize hydrophobic bonding. In several systems these is evidence that some nonsolvation contribution to theu _ij pair potential which is not explicitly accounted for in the models is important in the real systems. Quite possibly this contribution is due to dispersion forces or to the chargepolarizability interaction. On the whole, theA _ij parameters do not seem to depend upon the charges on solute particlesi andj; this is evidence that the model is fairly realistic.     

Studies of inorganic precipitate membrane. Part XXX. Membrane selectivity from electrical potential and conductivity measurements

Bi-ionic and multi-ionic potentials across parchment-supported mercuric sulfide membrane with various combinations of 1:1 electrlytes at different concentrations were measured. Membrane conductivity in contact with a single electrolyte was experimentally determined to evaluate selectivity of the membrane with the predetermined values of intramembrane mobility ratio. The selectivity sequence of the membrane was K⁺>Na⁺>Li⁺, which on the basis of the Eisenman–Sherry model of membrane selectivity, points toward the weak field strength of the charge groups attached to the membrane matrix. The permeability ratio of ions within the membrane was also evaluated by use of the equation based on the macroscopic linear laws of nonequilibrium thermodynamics derived by Sandblom and Eisenman. Three different methods of various integrated forms of the Nernst-Plank flux equation were used to derive the potentiometric selectivity constant K_ij^pot of the membrane. These values were close to one another.     

The reaction of 2,5-dimethylpyrrole with O2(a1Δg) in the gas phase

The chemical reaction of 2,5-dimethylpyrrole (C₆H₉N) with O₂(¹Δ_g) was studied in the gas phase in an isothermal flow reactor at room temperature and low pressures. The C₆H₉N concentration profiles were studied under pseudo-first order conditions [C₆H₉N]_° ? [O₂(¹Δ_g)] with mass-spectrometric detection of C₆H₉N. O₂(¹Δ_g) was produced either in a microwave discharge or in a chemical reaction. The value for the rate constant: was measured. The rate constant is compared to the value obtained for the quenching process. The primary product C₆H₉NO₂ was detected by mass spectrometry and the reaction mechanism is proposed. The possibility of using this reaction as a gas phase titration reaction for O₂(¹Δ_g) is discussed.     

Kinetic Analysis of Nonisothermal Decomposition of Acetyl Ferrocene

The work deals with thermal decomposition of acetyl ferrocene in nitrogen atmosphere based on nonisothermal thermogravimetry. It presents a mathematical analysis of nonisothermal thermogravimetric data using multiheating rates to estimate reaction kinetic parameters. Model free (integral isoconversional) methods are employed to analyze the thermogravimetric data. The decomposition is a multistep process. The activation energy E_α of decomposition is conversion (α) dependent. The average values of activation energy are E_α = 49.87, 106.28, and 183.35 kJ mol⁻¹ for three major steps of decomposition. The most probable reaction mechanism function, g(α), for thermal reactions has been identified by the master plot method, and the stepwise reaction mechanisms are found to be different for different steps. The estimated values of the activation energy E_α and g(α) have been utilized in the determination of the reaction rate A_α of thermal decomposition. The α‐dependent reaction rate values are determined and are found to lie in the range of 5.2 × 10⁵ to 3.2 × 10⁴ min⁻¹, 1.7 × 10¹⁵ to 7.8 × 10⁶ min⁻¹, and 3.8 × 10⁸ to 1.4 × 10⁷ min⁻¹ for three different steps. Based on the values of E_α, g(α), and A_α, the thermodynamic triplets (ΔS, ΔH, ΔG) associated with the decomposition reactions have been estimated. Estimated kinetic parameters have been used to construct the conversion curves, and those have been successfully compared with the experimentally observed ones.     

A test of the onsager reciprocal relations and a discussion of the ionic isothermal vector transport coefficientsI Ij for aqueous AgNO3 at 25°C

Values ofI _ij calculated from experimental data are given for AgNO₃ at 25°C. Experimental values of the ratioI ₁₂/I₂₁ are calculated to provide a sensitive direct test of the Onsager reciprocal relations,I ₁₂=I₂₁. This ratio is found to be unity within experimental error (ca. 2%). The general physical interpretation ofI _ij/N as mobilities is discussed. An approximate way of estimatingI _ij for dissociated salts is considered. A comparison is made between AgNO₃ I _ij data and corresponding data for NaCl and KCl. It is concluded that ion-pair formation (1) sharply increases the magnitude of the interaction mobility,I ₁₂/N; and (2) increases the intrinsic mobility of Ag⁺,I ₁₁/N, and decreases the intrinsic mobility of NO ₃ ^– ,I ₂₂/N.