AxMn1-xFe2O4铁氧体(A=Zn,Ni)中阳离子的占位有序化行为研究

基于尖晶石晶体结构信息,本文采用热力学三亚晶格模型,将材料热力学计算和第一性原理计算相结合,研究了Zn_xMn_(1-x) Fe_2O_4和Ni_xMn_(1-x)Fe_2O_4立方相中的Zn~(2+)、Ni~(2+)、Mn~(2+)以及Fe~(3+)在8a和16d亚晶格上的占位有序化行为。结果表明:在锰铁氧体中,室温下Mn~(2+)完全占据在8a亚晶格上,Fe~(3+)完全占据在16d亚晶格上,属于正尖晶石结构;随着热处理温度升高,在1 273 K达到热处理平衡时的占位构型为(Fe~(3+)0.09Mn~(2+)0.91)[Fe~(3+)1.91Mn~(2+)0.09]O_4,在热处理温度升至1 473 K时,达到热处理平衡时的占位构型为(Fe~(3+)0.11Mn~(2+)0.89)[Fe~(3+)1.89Mn~(2+)0.11]O_4,均与实验结果符合较好。在锌铁氧体中,室温下Zn~(2+)完全占据在8a亚晶格上,Fe~(3+)完全占据在16d亚晶格上,属于正尖晶石结构;在热处理温度较高时,Zn~(2+)和Fe~(3+)发生部分置换,符合实验结果。在镍铁氧体中,半数的Fe~(3+)在室温下占据在8a亚晶格上,Ni~(2+)与剩下另一半的Fe~(3+)共同占据在16d亚晶格上,仅在热处理温度较高的时候发生微弱变化,亦与已有的实验结果吻合。在此基础上,本文进一步通过热力学模型研究了立方相尖晶石结构的Zn_xMn_(1-x)Fe_2O_4、Ni_xMn_(1-x)Fe_2O_4复合体系中阳离子占位行为与热处理温度对占位的影响规律。     

Röntgenographische Bestimmung der thermischen Störung in den Kristalliten partiell kristallisierter Polyäthylene

Summary The dielectricα _a - andβ _a -absorptions in the linear high polymers whose dipoles are short and rigidly attached to their main chains are investigated theoretically and compared with our observed data. Suffix “a” represents that dielectric absorption comes from amorphous part. Examples of this kind are polyvinyl chloride, polyvinyl bromide, polyethylene isophthalate, polyethylene terephthalate and polyoxymethylene. Theα _a -absorptions are attributed to the re-orientations of their dipoles due to the segmental micro-Brownian motions of the polymer chains in the amorphous part. Theβ _a -absorptions seem to be caused by local micro-Brownian motions of the polymer chains. Theβ _a -absorptions are described by a model of local viscoelastic relaxations of the “dipoles” in the vicinity of their equilibrium directions. Here, the term “dipole” represents the resultant dipole of the permanent dipoles in the motional unit which has about the same order of magnitude as the monomer unit. Thus the various properties ofα _a - andβ _a -absorptions are calculated and agree with our observed values at least semi-quantitatively. In the second section the equations ofα _a - andβ _a -absorptions are derived. The properties of theα _a -absorptions are calculated in the third section and compared with our observed data. The magnitudes ofα _a -absorptions of the semi-crystalline polymers are smaller than those of the amorphous polymers even in the amorphous samples of the semi-crystalline-polymers. The temperature dependence of the magnitude ofα _a -absorption is far gentler in the crystalline polymer compared with the amorphous at temperatures higher than glass transition temperature (T _g ). These observed tendencies are explained by our theory. The calculated values of the activation energies ofα _a -absorptions are 50 ≈ 150 kcal/mol, the same orders as the observed values. The shape of theα _a -absorption is given by the form [ε(iω) -ε∞]/[ε ₀-g3 _∞] = [(1+iω π ₁ (1 +iωπ ₂)^−1/2 at temperatures higher thanT _g . This is in good agreement with the observed shape in the amorphous polymer, not only for the order of breadth but also for the order of asymmetry. The shape of theα _a -absorption in the semi-crystalline polymer is given by a superposition of the above formula and leads to the same order of breadth as the observed shape, too. The properties ofβ _a absorptions are calculated in the fourth section with the aid of the above mentioned model. The calculated values of the magnitudeβ _a -absorptions show fairly good agreement with the observed values too. The temperature dependence of the magnitude ofβ _a -absorption is discussed. The calculated values of the activation energies of theβ _a -absorptions are of the order 10 ≈ 20 kcal/mol, in good agreement with the observed values. The shape ofβ _a -absorption is also given by a superposition of the above formula and leads to the same order of breadth as the observed shape. The order of asymmetry of our theoretical absorption curve agrees with that of the observed curve.

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Vorgetragen auf der Sitzung des Fachausschusses Physik der Hochpolymeren im Verband der Deutschen Physik. Gesellschaft auf der Physikertagung in Wien, 21. Okt. 1961.

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Mit 11 Abbildungen und 3 Tabellen     

Interaction between two double layers for Na3PO4 types electrolytes at y0 > yd > 0

Interaction between two double layers for the Na₃PO₄ type electrolytes at y ₀ > y _d > 0 were investigated with the aid of λ parameter methods and the accurate numeral results were given. The maximum of the interaction energies between two double layers for A_v+ B_v- A_{v_ + } B_{v_ - } type electrolytes at y ₀ > y _d > 0 is independent of y ₀, but increases with y _d . The interaction energies between two double layers for NaCl, CaCl₂, FeCl₃, Na₂SO₄ and Na₃PO₄ type electrolytes at y ₀ = 5 and y _d = 2 were compared. If the negative or positive ions for A_v+ B_v- A_{v_ + } B_{v_ - } type electrolytes have the same charge number, the maximum of their interaction energies increases with the charge number of the ions of opposite charge. If the negative or positive ions of the electrolytes have different charge numbers, the relative heights of the maxima of their interaction energies are indefinite. For the in pairs conjugate type electrolytes like CaCl₂ and Na₂SO₄ or FeCl₃ and Na₃PO₄, the larger the charge number of the negative ions of the electrolytes is, the higher the maximum of their interaction energies is. The results for Na₃PO₄ type electrolytes at y ₀ > y _d > 0 can also be applied to FeCl₃ type electrolytes at y ₀ > y _d > 0.     

Theoretical studies on N-loss predissociation mechanisms of N2O+ (A?2Σ+) in Cs symmetry

The N-loss predissociation mechanisms of the A ²Σ⁺ (2 ² A′) state of N₂O⁺ to the first and second dissociation limits were studied in the C _s symmetry. The potential energy curves (PECs) and minimum energy crossing points (MECPs) for the C _s states of N₂O⁺ were calculated at the CAS levels. On the basis of our CAS calculation results (CASPT2 energetic results and CASSCF spin orbit couplings), we suggest two processes for N-loss predissociation mechanisms of A ²Σ⁺ (2 ² A′) to the first and second limits. The first two steps in the two processes are the same: A ²Σ⁺ passes through the 2 ² A′/1 ⁴ A″ MECP and then reaches the 1 ⁴ A″ (1 ⁴Σ⁻) PEC. The 2 ² A′/1 ⁴ A″ MECP has a bent geometry and is slightly higher in energy than the transition state along the 1 ⁴ A″ PEC. Our mechanisms are different from the previously suggested mechanisms (via 1 ⁴Π).     

Comparative XANES study on the two electron-doped high-Tc superconductor systems, (Sr,La)CuO2 and (Nd,Ce)2CuO4

Here we employ high-quality samples of (Sr_1−xLa_x)CuO₂ and (Nd_2−xCe_x)CuO₄ and XANES spectroscopy at O-K, Cu-L_2,3 and Ce-M_4,5 edges to gain comprehensive understanding of the electronic structure and doping in n-type high-T_c superconductors. Not only common but also slightly different features are revealed for the two systems. From O-K-edge spectra, the UHB is found essentially independent of the electron-doping level for both the systems, in line with our understanding that the doped electrons do not go to the O site in n-type copper-oxide superconductors. Another common observation is that the main Cu^II peak at the Cu-L₃ edge (due to transitions to the Cu^II-3d orbitals) systematically decreases in intensity upon electron doping, hence verifying the fact that the doped electrons go to the Cu site. The difference then between the two systems is that in (Sr_1−xLa_x)CuO₂ the weaker Cu^II peak due to transitions to the Cu^II-4s orbital depends on the degree of doping. Moreover, it was found that with increasing x, electron density increases much faster in (Sr_1−xLa_x)CuO₂ than in (Nd_2−xCe_x)CuO₄. This is a consequence of two phenomena: a tiny increase in oxygen content concomitant to the Ce^IV-for-Nd^III substitution and the somewhat lower Ce-valence value of +3.8 compared to the nominal tetravalent state.     

LixNi0.5Co0.5O2的态密度计算及电化学性能研究

>为获得综合性能更好的锂离子二次电池正极材料, 分析了Co掺杂对Li_xNiO₂电化学性能的影响. 采用密度泛函DFT理论对Li_xNiO₂和Li_xNi_0.5Co_0.5O₂的平均放电电压和态密度进行了计算. 同时, 用共沉淀法制备了Li_xNiO₂和Li_xNi_0.5Co_0.5O₂锂离子二次电池正极材料, 并对其进行了XRD结构分析和恒流充放电测试. 实验和计算结果表明: 随锂离子嵌入正极(电池放电), 电池的电压逐渐降低, 材料的态密度峰向低能量方向移动; 与Li_xNiO₂相比, Li_xNi_0.5Co_0.5O₂的电压平台相对较高(当0.25≤x≤0.5), 而且在Li^＋嵌/脱时, Li_xNi_0.5Co_0.5O₂的结构变化相对较小; Co离子的掺入, 减小了NiO₆八面体的畸变度, 使材料的电化学稳定性得以提高. 在钴掺杂镍酸锂体系中, NiO₆和CoO₆具有相互的稳定作用.     

The Potential Energies of Cohesion of a Crystalline Organic Enantiomer and the Racemate; on the Energy for the Liquid Racemate [1]

The cohesion potential energy of the crystal of one enantiomer of ethyl 3-cyano-3-(3,4-dimethyloxyphenyl)-2,2,4-trimethylpentanoate, −47.7 ± 0.1 kJ mol⁻¹ (0–90°C), was found out from the heat of sublimation (123.2 ± 5.1 kJ mol⁻¹, 78.6°C) and the kinetic energies for the gas phase and the crystal. It was found that the entropy function of Debye’s theory of solids mathematically agreed with the vibrational entropy of the gas (variationally obtained), allowing to disclose the vibrational energy using the Debye energy function (E _vib 835.0 kJ mol⁻¹ (78.6°C), E ⁰ included). E _kin for the crystal (771.1 kJ mol⁻¹ (78.6°C)) was obtained by Debye’s theory with the experimental heat capacity. The cohesion energy represented a moderate part of the sublimation energy. The cohesion energy of the racemic crystal, −44.2 kJ mol⁻¹, was obtained by the heat of formation of the crystal in the solid state (3.0 kJ mol⁻¹, 83.3°C) and E _kin for the crystal (by Debye’s theory). The decrease in cohesion on formation of the crystal accounted for the energy of formation. The change in potential energy on liquefaction of the racemate from the gas state was disclosed obtaining added-up E _{vib + rot} for the liquid in the way as to E _vib for the gas, the Debye entropy function being increasedly suited for the liquid (E _{vib + rot} 763.4 kJ mol⁻¹ (115.4°C)). Positive ΔE _pot, 13.0 kJ mol⁻¹, arised from the increase in electronic energy (Δ _l ν_mean − 154.3 cm⁻¹, by the dielectric nature of the liquid), added to the cohesion energy.     

The hard-sphere model for linear and regular star polybutadienes

The dilute solution properties of linear, 18-arm, and 270-arm star polybutadienes have been studied in a theta solvent and in a good solvent. Values of the radius of gyration R_G, the second virial coefficient A₂, the intrinsic viscosity [η], and the diffusion coefficient D₀ have been measured for each polymer. The ratios R_T/R_G, R_V/R_G, and R_H/R_G for each type of polymer are used to compare the four dilute solution properties. R_T is termed the “thermodynamic radius.” It is the radius of the hard sphere with the same excluded volume as the polymer coil. R_T is calculated from A₂ by R_T = (3A₂M₂/16ηN_A)^1/3. R_V and R_H are equivalent hard spheres defined for the intrinsic viscosity and translational diffusion coefficient, respectively. R_T/R_G, R_V/R_G, and R_H/R_G increase from about 0.7 for linear polymer coils as the number of arms in the star increases. Values of the ratios for the 18-arm stars are less than the value for the hard-sphere, but the values of the ratios of the 270-arm stars are equal to the hard-sphere limit within experimental error.     

Characterization of Ascentis RP-Amide column: Lipophilicity measurement and linear solvation energy relationships

This study investigates lipophilicity determination by chromatographic measurements using the polar embedded Ascentis RP-Amide stationary phase. As a new generation of amide-functionalized silica stationary phase, the Ascentis RP-Amide column is evaluated as a possible substitution to the n  -octanol/water partitioning system for lipophilicity measurements. For this evaluation, extrapolated retention factors, log k^′_w$\text{log}{k^{\prime }}_w$, of a set of diverse compounds were determined using different methanol contents in the mobile phase. The use of n-octanol enriched mobile phase enhances the relationship between the slope (S  ) of the extrapolation lines and the extrapolated log k^′_w$\text{log}{k^{\prime }}_w$ (the intercept of the extrapolation), as well as the correlation between log P   values and the extrapolated log k^′_w$\text{log}{k^{\prime }}_w$ (1:1 correlation, r² = 0.966). In addition, the use of isocratic retention factors, at 40% methanol in the mobile phase, provides a rapid tool for lipophilicity determination. The intermolecular interactions that contribute to the retention process in the Ascentis RP-Amide phase are characterized using the solvation parameter model of Abraham. The LSER system constants for the column are very similar to the LSER constants of the n-octanol/water extraction system. Tanaka radar plots are used for quick visual comparison of the system constants of the Ascentis RP-Amide column and the n-octanol/water extraction system. The results all indicate that the Ascentis RP-Amide stationary phase can provide reliable lipophilic data.     

A study of the Li1+xTi2−xO4 spinel system by diffuse-reflectance spectroscopy

The room-temperature diffuse-reflectance spectra of compositions within the Li_1+xTi_2?xO₄ spinel system ($\text{0 ≤ x ≤}\text{1}\text{3}$) show three absorption bands in the range 4000 to 48,000 cm^?1. Two high-energy absorption bands correspond to charge-transfer transitions from the oxygen-2p valence band to the titanium t_2g and σ1 conduction bands, where the σ1 band of e_g character has hybridized titanium-3d and titanium-4s parentage. The absorption band arising from promotion of electrons to the empty σ1 band does not alter with composition whereas the absorption band arising from promotion of electrons to the partially filled t_2g band narrows as the concentration of conduction electrons in the t_2g band decreases. These two high-energy absorption bands fall entirely within the ultraviolet spectral region, and the absorption edge in $\text{Li}{}_{\mathrm{<mtext>4</mtext><mtext>3</mtext>}}\text{Ti}{}_{\mathrm{<mtext>5</mtext><mtext>3</mtext>}}\text{O}{}_4\text{(x =}\text{1}\text{3}\text{)}$ occurs at 24,300 cm^?1 (3.02 eV). A low-energy absorption band is observed in compositions with $\text{x <}\text{1}\text{3}$ and in samples of $\text{Li}{}_{\mathrm{<mtext>4</mtext><mtext>3</mtext>}}\text{Ti}{}_{\mathrm{<mtext>5</mtext><mtext>3</mtext>}}\text{O}{}_4$ reduced in hydrogen at elevated temperatures. This band straddles the boundary between the visible and infrared spectral regions and shifts toward lower energy as the concentration of conduction electrons in the t_2g band decreases. The possible origins of the band are discussed; the argument is in favor of a d-d interband transition from states in the partially filled t_2g band to states in the empty σ1 band.     

Entwässerung von Kristallhydraten als Verfahren zur Reinigung von Salzen, 7. Mitt.: Über die Änderung der isomorphen Verunreinigung bei der Entwässerung von Na2SO4·10 H2O in dessen gesättigter Lösung bei der Übergangstemperatur sowie durch organische Flüssigkeiten

Zusammenfassung Es wurde die Gehaltsänderung der isomorphen Verunreinigung zweier Systeme: Na₂SO₄·10 H₂O/Na₂SeO₄·10 H₂O und Na₂SO₄·10 H₂O/Na₂CrO₄·10 H₂O während der Entwässerung sowohl in deren gesätt. Lösung bei der Übergangstemp. als auch durch Lösungsmittel (CH₃OH und C₂H₅OH) untersucht.Der nach beiden genannten Methoden durchgeführte Entwässerungsprozeß ist von einer Verminderung der isomorphen Verunreinigung begleitet. Der Reinigungskoeffizient (W) hängt mit der Beschaffenheit der isomorphen Verunreinigung und deren Konzentration im ursprünglichen Kristallhydrat zusammen. Wenn die Entwässerung unter Einwirkung organischer Lösungsmittel verläuft, istW auch noch von der Natur des Entwässerungsmittels selbst sowie von der Löslichkeit der isomorphen Verunreinigung im verwendeten Lösungsmittel abhängig.

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Dehydration of crystal hydrates as a method of purifying salts, VII: Investigation of the alteration of isomorphous contaminant content during the dehydration ofNa ₂ SO ₄·10 H₂ O in its saturated solution at the transition temperatur and by employing organic solvents

The change in the content of isomorphous contaminant of the two systems Na₂SO₄·10 H₂O/Na₂SeO₄·10 H₂O and Na₂SO₄·10 H₂O/Na₂CrO₄·10 H₂O during dehydratation has been investigated both in their saturated solution at the temperature of transition and by the solvents CH₃OH and C₂H₅OH.The dehydratation process, carried out by either method mentioned, is accompanied with a decrease of the isomorphous contaminant content in the crystalline mass. The coefficient of purification (W) depends on the nature of the isomorphous contaminant and its concentration in the initial crystallohydrate. In the case, when dehydratation takes place under the action of organic solvents,W depends also on the nature of the dehydratation agent itself, as well as on the solubility of the isomorphous contaminant in the employed solvent.

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Mit 2 Abbildungen     

Linear expansion of the eigenvalues of a Hermitian matrix and its application to the analysis of the electronic spectra of 3d ions in crystals

It is shown that the eigenvalues E_i of a Hermitian matrix H with matrix elements H_ij = Σ_kA^k_ija_k, where A^k_ij are known numbers and a_k a set of parameters, can be exactly expanded as $\text{E}{}_{\mathrm{i}}\text{= Σ}{}_{\mathrm{k}}\text{(}\text{?E}{}_{\mathrm{i}}\text{?a}{}_{\mathrm{k}}\text{)a}{}_{\mathrm{k}}$. This property is applied to the analysis of the optical spectra of transition metal ions in crystals proposed by L. Pueyo, M. Bermejo, and J. W. Richardson (J. Solid State Chem.31, 217, 1980), and it is shown that this method represents the best fit of the Hamiltonian eigenvalues to the observed (or calculated) spectrum. Further advantages of using this property, in connection with the spectral analysis, are the minimization of the errors associated with the numerical approximations and a reduction in computer time. In the molecular orbital calculation of the optical or uv spectra of these systems, this linear expansion of the eigenvalues give a detailed interpretation of the improvements produced by refined calculations, such as those including configuration interaction. In particular, the changes in one-electron energy and in open-shell repulsion interactions associated with the refinement can be clearly and easily formulated. As examples, the computed spectra of CrF^4?₆ and CrF^3?₆ are discussed.     

Numerical method of non-isothermal curve analysis by means of electrical resistance measurement during cooling

The temperature-dependence of the electrical resistance of Al-Zn 78 wt.% was measured during linear cooling of the samples in the range of eutectoidal decomposition. The resulting resistancevs. temperature curves were analysed by:

deriving the temperature-dependence of the volume fractionx(T) of theη precipitate;

fitting the theoretical functionx(T)=x _h (T)+x _c (T) following from numerical integration of the reaction rate equations for the simultaneously occurring homogeneous (H) and cellular (C) precipitation processes.

As a result, the activation energiesE _h andE _c , the JMA exponentsn _h andn _c , the rate constantsk _h andk _c , and the critical temperaturesT _o of the two processes were estimated.     

Synthesis and crystal structure of the A6B5O18 perovskite-like compounds

New members of the A_nB_n−1O_3n perovskite-like family (Ba₅KNb₅O₁₈ and Sr₆Nb₄SnO₁₈ compounds) with n = 6 have been synthesized and studied by the X-ray powder diffraction. Their crystal structures were found to belong to the Ba₆Nb₄TiO₁₈-type with a = 0.57840(7) nm, c = 4.2532(5) nm and a = 0.5661(1) nm, c = 4.186(1) nm for Ba₅KNb₅O₁₈ and Sr₆Nb₄SnO₁₈, respectively. It was shown that Ba and K (A-atoms) are completely disordered in the crystal structure of Ba₅KNb₅O₁₈ compound. But Nb and Sn atoms (B-atoms) in the crystal structure of the Sr₆Nb₄SnO₁₈ compound are quite ordered with the preferred Sn⁺⁴ and Nb⁵⁺ cations localization in the center of perovskite-like block and on the boundaries of these blocks, respectively. Temperature and frequency dependencies of the real components of electric conductivity σ^I and dielectric permeability ɛ^I; specific electric conductivity at the direct current σ_dc have been obtained by the impedance spectroscopy method for Sr₆Nb₄SnO₁₈.     

Comparative study of Cl<Superscript>−</Superscript>, Br<Superscript>−</Superscript>, and I<Superscript>−</Superscript> ions adsorption from dimethyl formamide at Hg- and Ga-electrodes

The adsorption of Cl⁻, Br⁻, and I⁻ ions from their 0.1 M solutions in dimethyl formamide at renewable liquid Hg- and Ga-electrodes was studied under similar experimental conditions by the differential-capacitance and jet-electrode methods. The data obtained points out to a strong effect of the metal nature on adsorption parameters and the halogenide-ion surface activity series. The halogenide-ion surface activity at the Hg-electrode increased in the following sequence: Cl⁻ < Br⁻ < I⁻; at the Ga-electrode, in the reverse sequence: I⁻ < Br⁻ < Cl⁻. The results are explained qualitatively in terms of the Andersen-Bockris model. It follows from the obtained data that (1) the free energy of the metal-halogenide-ion interaction increases in the following sequence: I⁻ < Br⁻ < Cl⁻; (2) the free energy of the Ga-halogenide-ion interaction exceeds that of the Hg⁻halogenide-ion interaction; and (3) the difference of the Cl⁻, Br⁻, and I⁻ ions interaction with the metals increased significantly when passing from Hg⁻ to Ga-electrode.     

X-ray diffraction study on the thermal expansion behavior of cellulose Iβ and its high-temperature phase

Oriented films of cellulose prepared from algal cellulose were hydrothermally treated to convert them into highly crystalline cellulose Iβ. The lateral thermal expansion behavior of the prepared cellulose Iβ films was investigated using X-ray diffraction at temperatures from 20 to 300 °C. Cellulose Iβ was transformed into the high-temperature phase when the temperature was above 230 °C, allowing the lateral thermal expansion coefficient of cellulose Iβ and its high-temperature phase to be measured. For cellulose Iβ, the thermal expansion coefficients (TECs) of the a- and b-axes were α_a = 9.8 × 10⁻⁵ °C⁻¹ and α_b = 1.2 × 10⁻⁵ °C⁻¹, respectively. This anisotropic thermal expansion behavior in the lateral direction is ascribed to the crystal structure and to the hydrogen-bonding system of cellulose Iβ. For the high-temperature phase, the anisotropy was more conspicuous, and the TECs of the a- and b-axes were α_a = 19.8 × 10⁻⁵ °C⁻¹ and α_b = −1.6 × 10⁻⁵ °C⁻¹, respectively. Synchrotron X-ray fiber diffraction diagrams of the high-temperature phase were also recorded at 250 °C. The cellulose high-temperature phase is composed of a two-chain monoclinic unit cell, a = 0.819 nm, b = 0.818 nm, c (fiber repeat) = 1.037 nm, and γ = 96.4°, with space group = P2₁. The volume of this cell is 4.6% larger than that of cellulose Iβ at 30 °C.     

Tetraalkylammonium Picrates in the Dichloromethane–Water System: Ion-Pair Formation and Liquid–Liquid Distribution of Free Ions and Ion Pairs

Equilibria concerning picrates of tetraalkylammonium ions (Me₄N⁺, Et₄N⁺, Pr₄N⁺, Bu₄N⁺, Bu₃MeN⁺) in a dichloromethane−water system have been investigated at 25 ^∘C. The 1:1 ion-pair formation constants (K _IP,o ^o) in dichloromethane at infinite dilution were conductometrically determined. The distribution constants (K _D ^o) of the ion pairs and the free cations between the solvents were determined by a batch-extraction method. The K _IP,o ^o value varies in the cation sequence, Bu₄N⁺ ≈ Pr₄N⁺ ≈ Et₄N⁺ < Bu₃MeN⁺ < < Me₄N⁺; this trend is explained by the electrostatic cation−anion interaction taking into account the structures of the ion pairs determined by density functional theory calculations. For the ion pairs of the symmetric R₄N⁺ cations, there is a linear positive relationship between log₁₀ K _D ^o and the number of methylene groups in the cation (N _{CH 2}). The ion pair of asymmetric Bu₃MeN⁺ has a higher distribution constant than that expected from the above log₁₀ K _D ^o versus N _{CH 2} relationship. These cation dependencies of log₁₀ K _D ^o for the ion pairs are explained theoretically by using the Hildebrand-Scatchard equation. For all the cations, the log₁₀ K _D ^o value of the free cation increases linearly with N _{CH 2}; the variation of log₁₀ K _D ^o is discussed by decomposing the distribution constant into the Born-type electrostatic contribution and the non-Born one, and attributed to the latter that is governed by the differences in the molar volumes of the cations. The cation dependencies of the ion-pair extractability and ion pairing in water are also discussed. An erratum to this article can be found at     

Theoretical study on the reaction mechanism of CH4 with CaO

The reaction pathways and energetics for the reaction of methane with CaO are discussed on the singlet spin state potential energy surface at the B3LYP/6-311+G(2df,2p) and QCISD/6-311++G(3df,3pd)//B3LYP/6-311+G(2df,2p) levels of theory. The reaction of methane with CaO is proposed to proceed in the following reaction pathways: CaO + CH₄ → CaOCH₄ → [TS] → CaOH + CH₃, CaO + CH₄ → OCaCH₄ → [TS] → HOCaCH₃ → CaOH + CH₃ or [TS] → CaCH₃OH → Ca + CH₃OH, and OCaCH₄ → [TS] → HCaOCH₃ → CaOCH₃ + H or [TS] → CaCH₃OH → Ca + CH₃OH. The gas-phase methane–methanol conversion by CaO is suggested to proceed via two kinds of important reaction intermediates, HOCaCH₃ and HCaOCH₃, and the reaction pathway via the hydroxy intermediate (HOCaCH₃) is energetically more favorable than the other one via the methoxy intermediate (HCaOCH₃). The hydroxy intermediate HOCaCH₃ is predicted to be the energetically most preferred configuration in the reaction of CaO + CH₄. Meanwhile, these three product channels (CaOH + CH₃, CaOCH₃ + H and Ca + CH₃OH) are expected to compete with each other, and the formation of methyl radical is the most preferable pathway energetically. On the other hand, the intermediates HCaOCH₃ and HOCaCH₃ are predicted to be the energetically preferred configuration in the reaction of Ca + CH₃OH, which is precisely the reverse reaction of methane hydroxylation.     

Fluorescence enhancement effect for the determination of DNA with calcein-cetyl trimethyl ammonium bromide system

A new spectrofluorimetric method was developed for the determination of trace amounts of DNA using the calcein as a fluorescent probe. In the presence of appropriate amounts of the cationic surfactant cetyl trimethyl ammonium bromide (CTAB), the anionic dye calcein dimerizes. The weak fluorescence intensity of the dimer was enhanced by adding DNA at pH 6–7. The interaction between calcein–CTAB and DNA was studied on the basis of this behavior and a new method was developed for determining DNA. Under the optimal conditions, the enhanced fluorescence intensity was in proportion to the concentration of DNA in the range of 4.0 × 10⁻⁶ to 8.0 × 10⁻⁵ g L⁻¹ for fsDNA and thermally denatured ctDNA (4.5 × 10⁻⁶ to 9.0 × 10⁻⁵ g L⁻¹). The detection limits (S/N = 3) were 2.0 × 10⁻⁶ and 2.2 × 10⁻⁶ g L⁻¹, respectively. This method was used for determining the concentration of DNA in synthetic samples with satisfactory results.