Proton mobility in the solid inorganic hydrates of acids and acid salts

The method for the calculation of the proton-transfer frequency (n_t) and its activation energies (E_t) was suggested. Results of the calculations were presented. The experimental data on the activation energy of proton-containing group rotation and protonconductivity values for some hydrates of inorganic acids and acid salts were compared with the calculated ones.     

Applicability of Sherwood correlations for natural organic matter (NOM) transport in nanofiltration (NF) membranes

A Sherwood correlation (mass transfer correlation) pertinent to natural organic matter–nanofiltration (NOM–NF) systems was established through the determination of the mass transfer coefficient (k) based on a combined film/thermodynamic approach, under laminar flow conditions. In this study, the NOM transport characteristics inside a NF membrane were quantitatively demonstrated through the pore Peclet number (Pe) calculated from experimental data. Transport experiments were performed, using a plate-and-frame crossflow test unit, at various feed flow rates, with a thin-channel type test cell that could be adjusted to different channel heights. The transport experimental results, with Suwannee River NOM (SRNOM), show that the transport of the SRNOM through the NF membrane (denoted as ESNA, MWCO of 200–250) was dominated by diffusion, which was further confirmed by the determined pore Pe (Pe < 1.0). The Sherwood correlation established for the SRNOM and NF membrane under ambient conditions (neither pH nor ionic strength adjustment) exhibited the standard form: Sh = 0.853Re^0.550Sc^0.363. The k values calculated by the correlations (k_Sh) were in good agreement with those determined from the experiments (k_exp). However, significant discrepancy between the k_Sh and k_exp was observed with alterations in the feed water chemistry. The k_Sh value increased with either decreasing pH or increasing ionic strength, as the experimentally determined diffusion coefficient of the SRNOM increased under these condition, whereas, the k_exp exhibited opposite trends, due to the decreased water permeation (or suction) rate, increased NOM transmission and decreased electrostatic repulsion. The k values for other source water NOM (but with the same membrane) were also estimated by the Sherwood correlation coupled with diffusion cell tests. The discrepancy between the k_Sh and k_exp values was less than 20%, and the discrepancy decreased with increased feed flow rate.     

Temperature dependence of the rate constant for reactions of hydrated electrons with H, OH and H2O2

The temperature dependence of the rate constants, for the reactions of hydrated electrons with H atoms, OH radicals and H₂O₂ has been determined. The reaction with H atoms, studied in the temperature range 20–250°C gives k(20°C) = 2.4 × 10¹⁰M^-1s¹ and the activation energy E_A = 14.0 kJ mol^-1 (3.3 kcal mol^-1). For reaction with OH radicals the corresponding values are, k(20°C) = 3.1 × 10¹⁰M^-1s^-1 and E_A = 14.7 kJ mol^-1 (3.5 kcal mol^-1) determined in the temperature range 5–175°C. For reaction with H₂O₂ the values are, k(20°C) = 1.2 × 10¹⁰M^-1s^-1 and E_A = 15.6 kJ mol^-1 (3.7 kcal mol^-1) measured from 5–150°C. Thus, the activation energy for all three fast reactions is close to that expected for diffusion controlled reactions. As phosphates were used as buffer system, the rate constant and activation energy for the reaction of hydrated electron with H₂PO₄^- was determined to k(20°C) = 1.5 × 10⁷M^-1s^-1 and E_A = 7.4 kJ mol^-1 (1.8 kcal mol^-1) in the temperature range 20–200°C.     

Update of the anharmonic force field parameters of the ozone molecule

A new set of spectroscopic constants of the ¹⁶O₃ molecule (ω_i, x_ij, y_ijk, γ^DD, _i^X, β_ij^X,…), which determine vibrational dependence of band centres and rotational parameters, is derived from recent accurate analysis of high-resolution experimental ro-vibrational spectra through the theoretical approach based on second-order perturbation expansions in normal coordinates accounting for Darling–Dennison resonance interactions. These values are used to update empirical values of anharmonic coefficients (k_ijl, k_ijlm) of the potential function expansion in normal coordinates. Quadratic f_rr, f_r, f_rr′, f as well as cubic f_rst and quartic f_rstl force constants in internal (bond lengths, bond angle) coordinates are also derived. A detailed discussion is devoted to the accuracy of parameter determination for each of four steps of calculations. It is emphasised that the conventional method based on the inversion of formulae of the perturbation theory gives the largest uncertainties at the last step of calculations: the determination of the anharmonic force field in internal coordinates.     

Thermogravimetric study on perovskite-like oxygen permeation ceramic membranes

The oxygen permeation properties of mixed-conducting ceramics SrFeCo_0.5O_3−δ (SFCO), Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCFO), La_0.2Sr_0.8Co_0.8Fe_0.2O_3−δ (LSCFO) and Ba_0.95Ca_0.05Co_0.8Fe_0.2O_3−δ (BCCFO) were studied by thermogravimetric method in the temperature range 600–900 °C. The results show that the oxygen adsorption rate constants k_a of all material are larger than oxygen desorption rate constants k_d and both k_a and k_d are not strongly dependent on temperature in the studied temperature range. The oxygen vacancy contents δ(N₂) and δ(O₂) in nitrogen and oxygen and their difference Δδ = δ(N₂) − δ(O₂) play an important role in determining the temperature behavior of oxygen permeation flux J_O2.     

Electric dipole moments of thietane in excited states of the ring puckering vibration: an experimental and ab initio study

The electric dipole moment in the ground state (v_p = 0) and the first five excited states (v_p = 1 … 5) of the ring puckering vibration of thietane have been determined from Stark shifts of rotational transitions. The results are: 0|μ_a|0 = 1.87583(16) D, 1|μ_a|1 = 1.87341(18) D, 2|μ_a|2 = 1.89759(28) D, 3|μ_a|3 = 1.88688(29) D, 4|μ_a|4 = 1.90036(18) D, 5|μ_a|5 = 1.88596(59) D. The dependence of these values on v_p shows the zig-zagging behaviour typical of modes with double minimum potentials. A combined analysis of the ground and first excited states yielded also a precise value for the transition moment, 0|μ_c|1 = 0.24023(49) D.

A potential and electric dipole moment function has been derived from ab initio calculations, using MP2 and the 6–31G** basis set. Expectation values of the dipole and transition moments were determined from these data. Absolute values are about 5% in error, but the variation with vibrational state is reproduced excellently by the theoretical values.     

Determination of the rates of formation and hydrolysis of the Schiff bases formed by pyridoxal 5′-phosphate and hydrazinic compounds

The macroscopic rate constants of formation (k₁) and hydrolysis (k₂) for the reactions of pyridoxal 5′-phosphate (PLP) with hydrazine (PLP-HY system), carbidopa (-hydrazino--methyl-β-(3,4-dihydroxyphenyl)propionic acid, PLP-CD system), hydralazine (1-hydrazinophthalazine, PLP-HL system) and isoniazid (4-pyridinecarboxylic acid hydrazide, PLP-ISO system) were fitted to a kinetic scheme that considers the different ionic species present in the medium, their protonation constants, and their individual rates of formation (k₁ⁱ) and hydrolysis (k₂ⁱ). The results obtained for the molecules bearing the hydrazine group are compared with those for the reactions of PLP with n-hexylamine (PLP-NHA system) and poly- -lysine (PLP-LYS system). Some structural effects on the individual rate constants are also examined.     

Pervaporation separation and mass transport of ethylbutanoate solution by polyether block amide (PEBA) membranes

Dense and composite membranes were developed from polyether block amide (PEBA). Polyacrylonitrile (PAN) and polysulfone (PSf) were used as the porous supports for the composite membranes. The membranes were tested for pervaporation separation of ethylbutanoate (ETB) solutions. Sorption and desorption experiments were also performed to provide data for analysis of mass transport based on resistance-in-series model.

The composite membranes with polyether block amide (PEBA) casted on PSf (PEBA/PSf) showed superior pervaporation performance than that casted on PAN (PEBA/PAN). The analysis of transport resistances revealed that: (1) the resistances in liquid boundary of ETB were highest and, therefore, were the controlling resistances; and (2) the transport resistances in the porous supports were much lower than those in the membrane top layers.

The results on plasticizing coefficients showed that ETB plasticized the membranes (positive, k_ii) but water did not (negative, k_jj). Negative coupling coefficients (k_ij) indicated that water reduced diffusivity of ETB in the membranes and the presence of ETB enhanced water diffusion in the membranes due to positive k_ji.     

Electroinitiated polymerization of styrene in dimethylsulphate

The electroinitiated polymerization of styrene in tetrabutylammonium perchlorate-dimethylsulphate solutions has been investigated. Polystyrene of low molecular weight is formed cationically through a direct monomer oxidation to the radical cation. Kinetic as well as mechanistic considerations for this system are made difficult by a number of factors: (a) the polymer is to a large extent insoluble in dimethylsulphate; (b) side reactions of both monomer and polymer tend to decrease the yields and therefore the calculated k_p values: (c) the supporting electrolyte concentration tends to affect the ionic equilibria in solution, so again influencing the k_p values.

A polymer degradation, found for polystyrene in LiClO₄-propylene carbonate solutions, was again noted and attributed to the effect of the current on the polymer covering the anode. The polymerization has no true termination, the only chain-stopping reactions being those giving rise to chain transfer.     

The kinetics of the chromic acid oxidation of diphenylmethane

The kinetics of the chromic acid oxidation of diphenylmethane in aqueous acetic acid solution has been studied. The rate law is v = k[φCH₂φ][CrO₃]h₀ a kinetic isotope effect, k_H/k_D = 6·4 at 30°, was noted, and electron releasing groups were found to moderately facilitate the reaction (⁺ = −1·17). These, and related data, suggest that the initial reaction is the abstraction of a hydrogen atom forming a benzhydryl radical. The latter may then be further oxidized to give the product, benzphenone. It is noted that the chromic acid oxidations which must involve hydrogen abstraction all show a kinetic dependence on the total chromium (VI) concentration, whereas those which are believed to proceed via an ester mechanism have a kinetic dependence on only the acid chromate ion. This difference is suggested as a possible method of distinguishing between these two mechanisms. The effect of the water content of the solvent on the rate of the reaction is discussed, and a tentative, relative, H₋ scale for some of these solutions is suggested. This may permit one to determine the number of molecules of water which are involved in a reaction.     

The kinetic isotope effect in the photochlorination of methane

The kinetic isotope effect for the photochemically initiated chlorination of methane-d₂ has been determined. The value is k_H/k_D = 12·1 at 0°C., and the variation with temperature is given by k_H/k_D = 1·09 exp (1300/RT. The results are considered in terms of a semiempirical potential energy surface, and the general subject of the magnitudes of primary kinetic isotope effects is discussed.     

Determination of the lumped mass transfer rate coefficient by frontal analysis

The validity of measurements of the lumped mass transfer rate coefficient (k_m,L) is studied on the basis of experimental data acquired under Langmuir isotherm conditions, in reversed-phase liquid chromatography. Two different methods were used, the perturbation method and frontal analysis. Accurate values of k_m,L can be properly obtained by the perturbation method because, with this method, the chromatographic processes take place under locally linear isotherm conditions. Values of k_m,L can also be derived from the breakthrough curves obtained in frontal analysis. Because the contribution of axial dispersion to band broadening was larger than that of the mass transfer resistances, the apparent axial dispersion coefficient (D_a) was first derived from the breakthrough curve by applying the equilibrium–dispersive model. Then, the value of k_m,L was calculated from D_a. The values of k_m,L determined by the two methods were in close agreement in the range of nondimensional Langmuir equilibrium constants (r=1/[1+K_LC₀]) between 0.32 and 0.85, irrespective of the mobile phase flow velocity. Thus, frontal analysis can be used for kinetic studies of the mass transfer in chromatographic columns.     

Carbon dioxide-water phase equilibria results from the Wong-Sandler combining rules

A model based upon the Peng-Robinson equation of state with the Wong-Sandler mixture combining rule (W-S MCR) can correlate phase equilibria in CO₂ + H₂O. The W-S MCR requires two energy parameters for liquid behavior and one interaction parameter for gas behavior, k_ij. In this paper, we present expressions for the energy parameters which cover a wide temperature range, and we use a new procedure to obtain k_ij by relating it to experimental cross second virial coefficients, B_ij. The three-phase pressures calculated for this system using our proposed model agree with the experimental data within a fraction of 1 bar. The correlated phase behavior of CO₂ + H₂O appears to be accurate over the ranges 1 – 1000 bar and 298.15–623.15 K. The proposed model also confirms the advantage of using the W-S MCR for phase equilibrium calculations.     

二级反应速率常数与活化能计算问题的讨论

In this paper, we discussed several problems on calculation of reaction rate constant in physical chemistry reference books. When calculating the rate constant k of the second-order reaction, we should make the half-life formula consistent with the reaction stoichiometric equation. And when calculating the activation energy with Arrhenius formula for ideal gas-phase reaction, attention should be paid to identifying the difference between the reaction rate constant k_c and k_p, as well as the difference between corresponding activation energy E_ac and E_ap. It is beneficial for students to have a correct understanding in calculation.     

Kinetics and mechanism of the reaction between silver(III) and thiourea in aqueous alkaline media

The tetrahydroxoargentate(III) ion, Ag(OH)₄⁻, is rapidly reduced by thiourea (tu) in accordance with the three term rate law RATE = {k₁+(k₂+k₃[OH⁻])[tu]}[Ag^III] where k₁ = 1.08 s⁻¹, k₂ = 1.46 x 10³ M⁻¹ s⁻¹, and k₃ = 2.02 x 10³ M⁻² s⁻¹. The k₁ path occurs via the rate-determining aquation of Ag(OH)₄⁻ while the other two paths involve axial attack of thiourea on silver. The higher values of k₂ and k₃ compared to the ethylenediamine reaction, which obeys the same rate law, is a reflection of the greater nucleophilicity of tu.

Following the redox reaction, solutions become brown in a reaction that obeys pseudo-first-order kinetics. Similar behaviour is observed when tu is replaced by Na₂S or thio-acetamide and when Ag^I reacts with any of these sulphur containing compounds. We attribute this process to the Ag^I promoted formation of sulphide species which eventually precipitate as Ag₂S.     

Neighboring hydrogen, isotope effect, and conformation in solvolysis of 3-methyl-2-butyl p-toluenesulfonate

In connection with hydrogen participation in solvolysis, 3-methyl-2-butyl p-toluenesulfonate is a marginal system. Comparison of the behavior of 3-D-3-methyl-2-butyl toluenesulfonate with that of the undeuterated analog discloses a substantial isotope effect on solvolysis rate, but only a small effect on product composition. The evidence points to a relatively high value of (k_Δ/k_s), the ratio of rate constants for anchimerically assited and unassisted solvolysis processes. Conformational considerations make understandable the relatively low degree of rate acceleration displayed by 3-methyl-2-butyl toluenesulfonate.     

Kinetics and mechanism of the oxidation of aliphatic aldehydes by sodium n-bromoarylsulphonam1des in acid solution

The oxidation of aliphatic aldehydes to the corresponding carboxylic acids by sodium N-bromoarylsulphonamides (N-bromoamines) is first order with respect to the oxidant, the aldehyde and hydrogen ions. In the oxidation of acetaldehyde at 298 K, the primary kinetic isotope effect, k_H/k_D is 4.91 ± 0.14 and the solvent isotope effect, k(H₂O)/k(D₂O), is 0.43. Addition of the parent sulphonamide does not affect the rate. The reduction of six substituted N-bromoamines exhibited a reaction constant of 1.22 at 298 K. (ArSO₂NH₂Br)⁺ is postulated as the reactive oxidising species. Separate rate constants for the oxidation of aldehyde hydrate and free aldehyde forms have been computed. The rates of the oxidation of the aldehyde hydrates correlate well with Taft's substituent constants with negative reaction constants. A mechanism involving hydride transfer from the aldehyde hydrate to the oxidant is proposed.     

Binary interaction parameter kij for calculating the second cross-virial coefficients of mixtures

The binary interaction parameters, k_ij, of 119 mixtures were determined by fitting the second cross-virial coefficients of mixtures with correlations for pure compounds [L. Meng, Y.Y. Duan, L. Li, Fluid Phase Equilib. 226 (2004) 109–120; L. Meng, Y.Y. Duan, Fluid Phase Equilib., 258 (2007) 29–33] and classical mixing rules. The mixtures included nonpolar/polar (associated), polar/polar, quantum/nonpolar (quantum) binaries. Very simple correlations for k_ij of H₂O/n-alkane, CO/nonpolar and quantum/nonpolar (quantum) binaries were successfully developed. The results show that the present correlations can accurately predict the second cross-virial coefficients.     

Ligand deprotonation significance in the formation of the molybdate ion-malic acid complexes

Using the temperature jump technique, the study of the kinetics of the complexing of oxomolybdate anion with malic acid has been carried out in aqueous solutions of pH 7.15–8.5 at ionic strength 0.1 M (KNO₃) and 25°'C. A reaction scheme for the formation of 1 : 1 complexes is proposed which accounts for the observed relaxation rates.

The significance of the ligand deprotonation on the complexation reaction of MoO₄²⁻ by a single protonated ligand, i.e. MoO₄²⁻+LH^nk→MoO₃(OH)Lⁿ⁻², (where n = 1 -, 2 -, etc), is analysed on the basis of a simple model. A linear correlation between the log k and the pK of the monoprotonated ligand (LH) is found for this reaction when the global process is controlled by the proton transfer from the ligand to an oxogroup, i.e. log k = a - 0.5xpK. It is found that this correlation is satisfied by MoO₄²⁻ and WO₄²⁻. The experimental slopes for these oxyanions are −0.503 and −0.543 respectively, in agreement with the predictions.     

Evaluation of the immobilized artificial membrane phosphatidylcholine: Drug discovery column for high-performance liquid chromatographic screening of drug–membrane interactions

Chromatographic retention factors (k′) of a series of eight β-adrenoceptor antagonist compounds (β-adrenolytic drugs) were determined employing an immobilized artificial membrane column (IAM.PC.DD). The influence of mobile phase pH, ionic strength, and organic modifier composition was studied in order to examine column performance. After the IAM.PC.DD columns were exposed to approximately 7000 column volumes of a 0.01 M PBS mobile phase, five out of six columns tested showed significant peak broadening and decreased k′ values indicative of premature column failure. The data suggested that the immobilized phospholipids stationary phase was removed by the 0.01 M PBS mobile phase. The β-adrenolytic drug's log k′_IAM values obtained with an IAM.PC.DD column were compared to an ^esterIAM.PC.MG column for predicting drug membrane interactions. For the linear regression analysis between log k′_IAM and the logarithm of the n-octanol–water partition coefficients (r_IAM.PC.DD=0.8710 vs. r_IAM.PC.MG=0.9538), the C₁₈ HPLC retention factors (r_IAM.PC.DD=0.8408 vs. r_IAM.PC.MG=0.9380), the liposome partition coefficients (r_IAM.PC.DD=0.8887 vs. r_IAM.PC.MG=0.9187), and various pharmacokinetic parameters, significantly better correlations were obtained with the ^esterIAM.PC.MG column than the IAM.PC.DD column.