Micellar Exchange Kinetics of Quaternary Ammonium Type Gemini Surfactants Monitored by Nuclear Magnetic Resonance

The dynamic NMR (DNMR) method was used to detect kinetic parameters of the molecular exchange process between monomers in bulk solution and those in the micelle for Gemini surfactants, 12-s-12 and 14-s-14(s=2, 3 and 4).The escape rate constant, k^-, was derived based on the simplified equations of DNMR theory, and the apparent activation energy of escape, E_a^-, was obtained based on the Arrhenius equation through temperature variation experiments.Results show that the orders of magnitude of k^- for 14-s-14 and 12-s-12 are respectively 10 and 10³ s^-1, E_a^- of 14-s-14 and 12-s-12 are respectively 54.04-73.64 and 33.42-47.09 kJ/mol.Furthermore, increases and E_a^- decreases with the spacer length growing.In combination with the micro-polarity measurements, it was revealed that molecules of 14-s-14 and 12-s-12 have to experience conformation changes when escaping from the micelles.The two-step molecular exchange mechanism for Gemini surfactants was therefore supported.     

Kinetics of the radiative relaxation of the highly excited C60 +* ion

The radiation of fullerene molecules from the intersection area of the C₆₀ beam with an electron beam with an energy of 27≤E _e /eV≤100 was studied experimentally under conditions of a single collision. It was found that ionized C₆₀ ^+* molecules make the main contribution to the radiation. The radiation intensity and the temperature of C₆₀ ^+* as functions of the energyE _e were measured. The kinetics of the radiation cooling of C₆₀ ^+* was studied and the rate of the radiation loss of the ion energy (5.5·10⁵ eV s⁻¹) was determined at a temperature of 3150 K. For the heat model of radiation at the wavelength λ=540 nm, this corresponds to the emissivity ε=1.1·10⁻². Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 273–276, February, 2000.     

Electron momentum density distribution in homonuclear diatomic molecules

Individual orbital contributions to the electron momentum densities of first-row homonuclear diatomic molecules are discussed. It is shown that the nodal surfaces in the orbital EMDs arise from a diffraction factor with both geometric and electronic components. The positions of the nodal surfaces convey information on the electronic structure. The results are illustrated with a Hartree-Fock-Slater calculation of the F₂(X¹Σ_g⁺) molecule.     

Study of Intermolecular Interaction in Dimethylsulphoxide + 1-Alkanols (1-Butanol, 1-Hexanol, 1-Octanol) At 303.15 K

Abstract

The ultrasonic velocity, u, viscosity, η, and density, ρ of dimethylsulphoxide (DMSO), 1-butanol, 1-hexanol, 1-octanol, and of their binary mixtures, where DMSO is common component, have been measured at 303.15 K. From the experimental data, excess isentropic compressibility, K ^E _s, excess intermolecular free length, L^E _f, excess velocity, u ^E, excess acoustic impedance, Z ^E, excess viscosity, η^E, excess free energy of activation of viscous flow, G?^E, and excess rheochore, [R ^E] have been calculated. The behaviours of excess functions with composition of the mixtures suggest that the structure-breaking effect dominates over the interaction effect between the component molecules. Furthermore, the experimental values of u and η were fitted by empirical equations stating their dependence on composition of the mixtures. The experimental values of u have been compared with those calculated by using Nomoto and Van Dael relations.     

The position of the VO3−4 charge-transfer transition as a function of the VO distance

The lowest singlet excited states of the VO^3?₄ complex are calculated as a function of the VO bond distance using the Hartree-Fock-Slater discrete variational method. The calculated average singlet transition energies ¹ΔE(?₁ → 2e) support assignments made before.     

Analysis of exponent values in Gaussian‐type functions for development of protonic and deuteronic basis functions

We analyzed the exponent (α) values in Gaussian‐type functions (GTF) for protons and deuterons in BH₃, CH₄, NH₃, H₂O, HF, and their deuterated molecules for the development of nuclear basis functions, which are used for molecular orbital (MO) calculations that directly include nuclear quantum effects. The optimized α (α_opt) value in the single s‐type ([1s]) GTF for protons is changed due to the difference in flexibility of the electronic basis sets. The difference between the energy obtained by using the α_opt value for each molecule and that obtained by using the average α (α_ave) value for these exponents with the 6‐31G(d,p) electronic basis function is only 2 × 10^?5 a.u. The α_ave values of protonic and deuteronic [1s] GTFs by the present calculation are 24.1825 and 35.6214, respectively. We found that the α_ave values enable the evaluation of the total energy and the geometrical changes in hydrogen bonding, such as O…H? O, O…H? N, and O…H? C, while the α_opt value became small by forming a hydrogen bond. The result using only the [1s] GTF for the protonic and deuteronic basis functions is sufficient to explain the differences of energy and geometry induced by the H/D isotope effect, although the total energy of ～5 × 10^?4 a.u. was improved by using the s‐, p‐, and d‐type ([1s1p1d]) GTFs for protons and deuterons. We clearly demonstrate that the protonic and deuteronic basis functions based on the α_ave value enable us to apply the method to other sample molecules (glycine, malonaldehyde, and formic acid dimer). The protonic and deuteronic basis functions we developed treat the quantum effects of protons and deuterons effectively and extend the application range of the MO calculation to include nuclear quantum effects. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Volumetric and Ultrasonic Behaviour of 1-Heptanol with Some Chloroethanes and Chloroethenes at 303.15 K

Abstract

Excess volumes (V^E ) and deviations in isentropic compressibilities (K_s ) were reported over the entire mole fraction range for mixtures of 1-heptanol with 1,2-dichloroethane, 1,1,1-trichloroethane, 1,1,2,2-tetrachloroethane, trichloroethene and tetrachloroethene, at 303.15 K. The values of V^E and K_s are positive for the systems, 1-heptanol + 1,2-dichloroethane, +1,1,1-trichloroethane, + trichloroethene and + tetrachloroethene. Inversion in sign of V^E and K_s from positive to negative is observed in mixtures of 1-heptanol with 1,1,2,2-tetrachloroethane. The experimental data were used to explain the effect of successive chlorination and unsaturation of ethane molecule on V^E and K_s .     

Thermodynamics of mixtures of hexane and heptane isomers with normal and branched hexadecane

Molar excess mixing enthalpies h ^E , Gibbs free energies g ^E and hence entropies s ^E have been obtained using calorimetry and the vapor sorption method at 25°C for hexane isomers+2,2,4,4,6,8,8-heptamethylnonane, a highly branched C ₁₆ . The h ^E and g ^E are negative while Ts ^E are positive, but small. The values are explained by the Prigogine-Flory theory through negative free volume contributions to h ^E and Ts ^E , counterbalanced in the case of Ts ^E by the positive combinatiorial Ts ^E for mixing molecules of different size. No contribution is seen from the interaction between methyl and methylene groups. The excess quantities are also obtained for hexane and heptane isomers mixed with n-hexadecane. Values of h ^E and Ts ^E are now strongly positive, while those of g ^E are only slightly less negative. The interpretation requires two recently advanced contributions in addition to those of the Prigogine-Flory theory: 1) a decrease of order when correlations of orientations between n-C ₁₆ molecules in the pure liquid are replaced in the solution by weaker correlations whose strengths depend on the shapes of the lower alkane isomers. For lower alkane isomers of the same shape, but highly sterically hindered, h ^E and Ts ^E are small, manifesting, 2) a negative contribution, ascribed to a rotational ordering of n-C ₁₆ segments on the sterically-hindered molecule. Enthalpy-entropy compensation is observed for these new contributions, arising from their rapid fall-off with increase of temperature.     

Non-isothermal oxidation kinetics of single- and multi-walled carbon nanotubes up to 1273 K in ambient

Non-isothermal oxidation kinetics of single- and multi-walled carbon nanotubes (CNTs) have been studied using thermogravimetry up to 1273 K in ambient using multiple heating rates. One single heating rate based model-fitting technique and four multiple heating rates based model-free isoconversional methods were used for this purpose. Depending on nanotube structure and impurity content, average activation energy (E _a), pre-exponential factor (A), reaction order (n), and degradation mechanism changed considerably. For multi-walled CNTs, E _a and A evaluated using model-fitting technique were ranged from 142.31 to 178.19 kJ mol⁻¹, respectively, and from 1.71 × 10⁵ to 5.81 × 10⁷ s⁻¹, respectively, whereas, E _a for single-walled CNTs ranged from 83.84 to 148.68 kJ mol⁻¹ and A from 2.55 × 10² to 1.18 × 10⁷ s⁻¹. Although, irrespective of CNT type, the model-fitting method resulted in a single kinetic triplet i.e., E _a, A, and reaction mechanism, model-free isoconversional methods suggested that thermal oxidation of these nanotubes could be either a simple single-step mechanism with almost constant activation energy throughout the reaction span or a complex process involving multiple mechanisms that offered varying E _a with extent of conversion. Criado method was employed to predict degradation mechanism(s) of these CNTs.     

Effect of the exchange integral K2s2p on the 2p-orbitals of the 1P and 3P states of the beryllium isoelectronic sequence arising from the configuration (1s)2(2s)(2p)

The ¹P and ³P states arising from the configuration (1s)²(2s)(2p) of the Be isoelectronic sequence are investigated. In the single configuration approximation, the energies of the two states are expressed as E⁰ + K_2s2p and E⁰ - K_2s2p, respectively. K_2s2p is the exchange integral between the 2s and 2p electrons and E⁰ is the energy of a model in which K_2s2p is deleted. First we calculate the 2s- and 2p-orbitals in this model. Second, by taking account of K_2s2p in this model, effects of this term on the 2p-orbitals in the ^1,3P states are investigated. In this manner, an explanation is given for the following facts which are obtained from a minimal Slater-type orbital set; (1) for Be and B⁺, the 2p-orbital of the ¹P state is broader than that of the ³P state; (2) for C²⁺, the extension of the 2p-orbital in the two states is almost the same; (3) for O⁴⁺ and Ne⁶⁺, in contrast to Be and B⁺, the 2p-orbital of the ¹P state is tighter than that of the ³P state.     

A method for determining the mean translational energy of particles desorbed from solid surfaces

A method for determinig the mean molecular translational energy in gas flows of low intensity (10¹²–10¹⁴ molec. s^–1) has been proposed. The method was verified using various gases (H₂, N₂, O₂, and CO₂ flowing into a vacuum out of a heated capillary. The translational energies were determined for CO and N₂ molecules desorbing from the surface of polycrystalline Ir. The translational temperature (T _tr) measured for CO equals 650±90 K and almost coincides with the surface temperature (T _s = 600 K). In the case of nitrogen molecules,T _tr = 4600±500 K atT _s = 500 K. The method proposed is applicable to the determination of the spatial distribution of molecular beam particles.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 30–34, January, 1995.The authors express their gratitude to A. V. Sklyarov for fruitful discussions during the elaboration of the theoretical basis and technical realization of the method.The reseach was carried out with the partial financial support of the International Science Foundation (Grant MBN 000).     

Physicochemical Properties and Surface Tension Prediction of Mixed Surfactant Systems: Triton X‐100 with Dodecylpyridinium Bromide and Triton X‐100 with Sodium Dodecylsulfonate

Dependences of the surface tension of aqueous solutions of ionic (dodecylpyridinium bromide, sodium dodecylsulfonate) and nonionic (Triton X‐100) surfactants and their mixtures on total surfactant concentration and solution composition were studied, and the surface tension of the mixed systems were predicted using different Miller's model. It was found that how to select the model for calculation of ω is corresponding to the degree of the deviation from the ideality during the adsorption of mixed surfactants. The compositions of micelles and adsorption layers at air‐solution interface as well as parameters (β^m, β^ads) of headgroup‐headgroup interaction between the molecules of ionic and nonionic surfactants were calculated based on Rubingh model. The parameters (B₁) of chain‐chain interaction between the molecules of ionic and nonionic surfactants were calculated based on Maeda model. The free energy of micellization calculated from the phase separation model (ΔG ₂ ^m ), and by Maeda's method (ΔG ₁ ^m ) agree reasonably well at high content of nonionic surfactant. The excess free energy ΔG _ads ^E and ΔG _m ^E (except α=0.4) for TX‐100/SDSn system are more negative than that TX‐100/DDPB system. These can be probably explained with the EO groups of TX‐100 surfactant carrying partial positive charge.     

Energy characteristics of adsorbed water in active carbons according to the NMR relaxation data

Nuclear magnetic relaxation measurements were used to determine activation energy E _act of the motion of water molecules adsorbed in active carbons. The E _act value was found to depend on the filling of active carbon pores due to changes in the state of water molecules under adsorption. It was established that the E _act = f(p/p _s) plots, where p/p _s is the relative pressure of water vapor observed for microporous active carbons (FAS-1, 2, N-15, SKT-6A), are similar in form to the corresponding plots of changes in water adsorption heats. In particular, we concluded that the plateau in the E _act = f(p/p _s) dependences, as in the case of adsorption heats, reflects the volumetric filling of active carbon micropores with water. We show that a linear function describes the increase in E _act values for water upon the complete filling of micropores with an increase in the volume of adsorbed water clusters per one primary adsorption center (W ₀/a _m ). We establish that, for water in the FAS-3 sample, the deviation of E _act values from this linear function was due to the contribution from the vapor phase in the mesopores (x ₀ = 0.7−1.2 nm) that make up a considerable part of the active carbon’s porous system.     

Thermal Decomposition of Some Chemical Compounds Used As Food Preservatives and Kinetic Parameters of This Process

Thermal decomposition processes of selected chemicals used as food preservatives such as sodium formate, sodium propionate, sodium nitrates(V and III) and sodium sulphate(IV) were examined by the derivatographic method. Based on the curves obtained, the number of decomposition stages and characteristic temperatures of these compounds have been found. Mass decrements calculated from TG curves ranged from 28.9% for sodium formate to 77.8% for sodium nitrate(V), while sodium sulphate showed a mass increment of 5.6%. Kinetic parameters such as activation energy (E _a ), frequency factor (A ) and reaction order (n ) were calculated from TG, DTG and T curves. Sodium formate shows the highest values of E _a and A which amount to 171.7 kJ mol^–1 and 5.8⋅10¹⁴ s^–1 , respectively, while the lowest ones, E _a =28.2 kJ mol^–1 and A =3.65⋅10² s^–1 belong to sodium nitrate(V). This revised version was published online in August 2006 with corrections to the Cover Date.     

Conformational Analysis of Biphenyl Derivatives. I. A Novel Steric Constant from the Internal Rotation Rate of 2,2′‐Bis‐(N‐Substituted Carbamoylmethyl)Biphenyl by Means of Dynamic NMR

A novel scale of steric substituent constant E_s^D is defined from the correlation of the logarithms of the internal rotation rate (k_r) at 393 K with Hancock (E_s^c) steric constant by means of dynamic NMR. In the inhibition of Pseudomona species lipase by 2,2′‐bis‐(N‐substituted carbamoylmethyl)biphenyls (1‐8), the logarithms of bimolecular rate constants are multiply correlated with both the Taft substituent constant σ* and E_s^D.     

X‐Ray Emission Spectroscopy: A Spectroscopic Measure for the Determination of NO Oxidation States in Fe–NO Complexes

Extensive study of the electronic structure of Fe‐NO complexes using a variety of spectroscopic methods was attempted to understand how iron controls the binding and release of nitric oxide. The comparable energy levels of NO π* orbitals and Fe 3d orbitals complicate the bonding interaction within Fe? NO complexes and puzzle the quantitative assignment of NO oxidation state. Enemark–Feltham notation, {Fe(NO)_x}ⁿ, was devised to circumvent this puzzle. This 40‐year puzzle is revisited using valence‐to‐core X‐ray emission spectroscopy (V2C XES) in combination with computational study. DFT calculation establishes a linear relationship between ΔE_σ2s*‐σ2p of NO and its oxidation state. V2C Fe XES study of Fe? NO complexes reveals the ΔE_σ2s*‐σ2p of NO derived from NO σ_2s*/σ_2p→Fe_1s transitions and determines NO oxidation state in Fe? NO complexes. Quantitative assignment of NO oxidation state will correlate the feasible redox process of nitric oxide and Fe‐nitrosylation biology.     

Study of molecular interaction in binary liquid mixtures of ethyl acetoacetate with chloroform and dimethylsulphoxide using excess acoustic parameters and spectroscopic methods

Densities and ultrasonic velocities were measured for binary liquid mixtures of ethyl acetoacetate (EAA) with chloroform (CHCl₃) and dimethylsulphoxide (DMSO) over the entire composition range. These experimental values were used to calculate the adiabatic compressibility (βs), intermolecular free length (L_f), excess molar volume (V^E), excess adiabatic compressibility (β_s^E) and excess intermolecular free length (L_f^E) for the liquid mixtures under consideration. In all the excess parameters, a positive deviation was observed in CHCl₃–EAA binary mixture, whereas a slight negative deviation was found for EAA–DMSO binary liquid mixture. These deviations were explained in terms of molecular interactions between like and unlike molecules and further affirmed by UV–Vis spectroscopic measurements in terms of polar and non-polar environment in the close proximity of solvatochromic dye. Fourier transform infrared spectroscopy (FT-IR) and proton-nuclear magnetic resonance (H¹ NMR) measurements have also been done to explain the molecular interaction in the binary liquid mixtures.     

On the energy difference between the lP and 3P states of the beryllium isoelectronic sequence

Wave functions of the ¹S (ground state), ³P and ¹P states for the beryllium isoelectronic sequence have been obtained in various approximations. The HF ²p orbitals for the ¹P and ³P states are similar except for Be, where the ²p orbital is quite diffuse for the ¹P state. The difference between the experimental E(¹P) – E(³P) and the HF E(¹P) – E(³P) is 0.62 eV for Be and 1.17 ～ 1.40 eV for B⁺ ～ F⁵⁺. The disagreements are attributed to the correlation effects between the 2s and 2p electrons. This is confirmed by ci calculations. It is shown that a limited basis SCF calculation reproduces the above feature of the HF results if we treat the orbital exponents as the variational parameters. The use of the Slater values for the orbital exponents is shown to be inadequate especially for the Be ¹P state. The conclusions of this paper will be useful for discussing the V–T separations of H₂ and C₂H₄.     

Absolute rate constants for the addition of hydroxymethyl radicals to alkenes in methanol solution

Absolute rate constants and their temperature dependencies were determined for the addition of hydroxymethyl radicals (CH₂OH) to 20 mono- or 1,1-disubstituted alkenes (CH₂ = CXY) in methanol by time-resolved electron spin resonance spectroscopy. With the alkene substituents the rate constants at 298 K (k₂₉₈) vary from 180 M^?1s^?1 (ethyl vinylether) to 2.1 middot; 10⁶ M^?1s^?1 (acrolein). The frequency factors obey log A/M^?1s^?1 = 8.1 ± 0.1, whereas the activation energies (E_a) range from 11.6 kJ/mol (methacrylonitrile) to 35.7 kJ/mol (ethyl vinylether). As shown by good correlations with the alkene electron affinities (EA), log k₂₉₈/M^?1s^?1 = 5.57 + 1.53 · EA/eV (R² = 0.820) and E_a = 15.86 ? 7.38 · EA/eV (R² = 0.773), hydroxymethyl is a nucleophilic radical, and its addition rates are strongly influenced by polar effects. No apparent correlation was found between E_a or log k₂₉₈ with the overall reaction enthalpy. © 1995 John Wiley & Sons, Inc.     

Enhancement of the bimolecular reaction of hydrogen iodide by vibrational excitation

The bimolecular reaction of HI in CO₂, which was excited vibrationally by irradiation of a continuous-wave CO₂ laser light, was investigated in the temperature range of 721–980 K. An enhancement of the reaction rate by a factor of about 2.5 was observed in the 1:1 HI? CO₂ mixture in comparison with the rate in pure HI when both sample gases were irradiated by a CO₂ laser (50 W) at 1 torr. However, in the HI-SF₆ mixtures the decomposition rate of HI was not accelerated by irradiation of the CO₂ laser. Thus the enhancement is attributed to vibrational excitation of HI through collisional energy transfers from laser-excited CO₂ (00°1). At lower total pressures or at lower partial pressures of HI in HI-CO₂ mixtures the enhancement was more significant because of inefficient vibrational deactivation of excited HI. A model calculation gave the result in agreement with the experimental one if the effective activation energy is assumed as E_a? = E_a - αE_vib, where E_a is the activation energy for the thermal reaction, E_vib is the vibrational energy of two colliding HI molecules, and α is estimated to be about 0.7. This means that a part of the vibrational energy of reacting HI is employed to reduce the activation energy for the translational or rotational degree of freedom.