CH4, CO2和H2O在非金属原子修饰石墨烯表面的吸附

煤层气(矿井瓦斯)是一种有望替代传统化石燃料，如煤、石油和天然气的非常规气体. 作为可得的清洁能源，它的利用被认为是节能和经济的选择. 在本工作中，非金属原子X(X=H，O，N，S，P，Si，F，Cl)修饰的石墨烯(Gr)被用来代表具有结构异性的煤表面模型. 通过密度泛函理论系统地研究了煤层气组分Y(Y=CH₄，CO₂，H₂O)在非金属原子修饰石墨烯上的吸附作用. 结果表明Y在非金属原子修饰石墨烯上的吸附均为物理吸附. 态密度和差分电荷密度共同表明了这种弱的相互作用.其中，H和Cl对CH₄的作用较大； N、O、F、Cl对CO₂的作用较强； N，Cl对H₂O的影响不容忽视. 总的来说，吸附能大小依次为：H₂O>CO₂>CH₄. 因此，在CH₄富集的煤层里注入H₂O或CO₂可以与CH₄形成竞争吸附，进而提高煤层气采收率. 本工作提供了在分子水平下煤层气与非金属原子修饰石墨烯之间的相互作用的详情，并为煤层瓦斯的开采与分离提供了有用的信息.     

Density functional theory study of vibrational spectra, and assignment of fundamental vibrational modes of succinimide and N-bromosuccinimide

This work deals with the vibrational spectroscopy of succinimide and N-bromosuccinimide. The mid and far FTIR and FT-Raman spectra were measured in the condensed state. The fundamental vibrational frequencies and intensity of vibrational bands were evaluated using density functional theory (DFT) using standard B3LYP/6-31G(*) and B3LYP/6-311+G(**) methods and basis set combinations. The vibrational spectra were interpreted, with the aid of normal coordinate analysis based on a scaled quantum mechanical force field. The infrared and Raman spectra were also predicted from the calculated intensities. Comparison of simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes. Unambiguous vibrational assignment of all the fundamentals were made using the total energy distribution (TED).     

钒氧阴离子团簇与小分子碳氢化合物反应的实验和理论研究

为了在分子层次上揭示相关催化反应的机理, 人们对过渡金属氧化物团簇与碳氢化合物分子反应进行了大量研究. 相比于过渡金属氧化物团簇阳离子, 阴离子对一些碳氢化合物的活性弱得多, 因此研究还很少. 在本工作中, 我们通过激光溅射产生钒氧团簇阴离子VxOy, 产生的团簇在接近热碰撞条件下与烷烃(C2H6和C4H10)以及烯烃(C2H4和C3H6) 在一个快速流动反应管中进行反应, 飞行时间质谱用来检测反应前后的团簇分布. 在VxOy与烷烃的反应中, 生成了产物V2O6H-和V4O11H-; 在与烯烃的反应中, 产生了相应的吸附产物V4O11X-(X=C2H4或C3H6). 密度泛函理论计算表明: V2O-6和V4O-11可以活化烷烃(C2H6和C4H10)的C—H键, 也可以与烯烃(C2H4和C3H6)发生3+2环化加成反应形成一个五元环结构(-V-O-C-C-O-), C—H键活化与环加成反应都需经历可以克服的反应能垒. 理论计算与实验观测结果相符合. V2O-6和V4O-11团簇都具有氧原子自由基(O·或O-)的成键特征, 活性O-物种也经常出现在钒氧催化剂表面, 因而本研究在分子水平上, 揭示了表面活性氧物种与碳氢化合物反应的机理.     

Apparent molal volumes of aqueous solutions of bis-tetraalkylammonium salts at 25°C: Methylene-group contribution to the limiting molal volume

Densities of aqueous solutions of a series of polymethonium chloride and bromide salts (CH₃)₃–N–(CH₂)_n–N–(CH₃)₃X₂ have been measured at 25°C. Apparent molal volumes have been calculated, and methylene-group contributions to the limiting apparent molal volumes °_v have been estimated. Constant values of the methylene-group contribution of 16.5 and 17.0 cm³-mole^–1 were obtained for the bromide and chloride salts, respectively. These values are consistent with methylene-group contributions reported for other series of organic electrolytes.     

Marginal electron density and density-difference functions

Summary For visual analysis of the density reorganization and distortion, the one-dimensional cut (x, y ₀,z ₀) and the two-dimensional cut (x, y, z ₀) of the three-dimensional electron density difference function (x, y, z) are frequently employed. However, these cut functions do not satisfy any sum rules in contrast to the original difference function (x, y, z). To avoid this difficulty, the use of the marginal electron density functions _x (x) and _xy (x, y) and their difference functions _x (x) and _xy (x, y) is proposed. The marginal densities are condensation of the three-dimensional density onto a particular plane or line of our interest, and they satisfy the sum rule (i.e., the conservation of the number of electrons) exactly. Some basic properties of the marginal electron density are clarified for typical diatomic molecular orbitals. An illustrative application is given for the bonding and antibonding processes in the H₂ system.     

Study of Densities, Viscosities and Ultrasonic Speeds of Binary Mixtures Containing 1,2-Dimethoxyethane and an Alkan-l-ol at 298.15 K

The viscosity deviation (Δη), the excess molar volume (V ^E) and the ultrasonic speed (u) have been investigated from viscosity (η) and density (ρ ) measurements of binary liquid mixtures of 1,2-dimethyoxyethane with methanol, ethanol, propan-1-ol, butan-1-ol, pentan-1-ol, hexan-1-ol or octan-1-ol over the entire range of composition at 298.15 K. The excess volumes are negative over the entire range of composition for all of the mixtures with the exception of hexan-1-ol and octan-1-ol. The excess isentropic compressibilities (K _S ^E) and viscosity deviations are negative for all of the mixtures. The magnitudes of the negative values of V ^E decrease with the number of carbon atoms of the alkan-1-ol. The trend of increasing K _S ^E values with the chain length of the alkanol is similar to that observed in the case of V ^E. Graphs of V ^E, Δ η, K _S ^E, Δ u, L _f ^E and Z ^E against composition are presented as a basis for a qualitative discussion of the results.     

A theoretical study of radical-only and combined radical/carbocationic mechanisms of arachidonic acid cyclooxygenation by prostaglandin H synthase

Prostaglandin H synthase catalyzes the oxygenation of arachidonic acid into the cyclic endoperoxide, prostaglandin G₂ (PGG₂), and the subsequent reduction of PGG₂ to the corresponding alcohol, prostaglandin H₂ (PGH₂), the precursor of all prostaglandins and thromboxanes. Both radical abstraction by a neighboring tyrosyl radical and combined radical/carbocationic models have been proposed to explain the cyclooxygenase part of this reaction. We have used density functional theory calculations to study the mechanism of the formation of the cyclooxygenated product PGG₂. We found an activation free energy for the initial hydrogen abstraction by the tyrosine radical of 15.6 kcal/mol, and of 14.5 kcal/mol for peroxo bridge formation, in remarkable agreement with the experimental value of 15.0 kcal/mol. Subsequent steps of the radical-based mechanism were found to happen with smaller barriers. A combined radical/carbocation mechanism proceeding through a sigmatropic hydrogen shift was ruled out, owing to its much larger activation free energy of 36.5 kcal/mol. Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s00214-003-0476-9. Electronic Supplementary MaterialSupplementary material is available in the online version of this article at Electronic Supplementary Material: Supplementary material is available in the online version of this article at     

聚γ-[N,N-双(β-乙硫乙基)胺基]丙基硅氧烷铑配合物的合成及其催化硅氢化性能

从二(β-氟乙基)烯丙胺出发,通过乙硫醚化、硅氢加成、气相法二氧化硅固载,再与三氯化铑作用,合成了标题配合物,它们是烯烃与三乙氧基硅烷的硅氢加成反应的有效催化剂,对其催化特性进行了研究。     

Temperature Dependent Dielectric Relaxation in Solvent Mixtures at Microwave Frequencies

By the use of time domain reflectometry method, dielectric measurements were carried out on dimethylformamide‐2‐nitrotoluene solvent mixtures in the frequency range 10 MHz‐20 GHz, at various temperatures from 15 °C to 45 °C. These solvent mixtures as well as pure solvents display a Debye type dispersion. Their frequency dependent dielectric properties can be summarized by the three parameters in the Debye equation: a static permittivity, permittivity at high frequency and a dielectric relaxation time constant. The free energy of activation for dipolar relaxation process and the Kirkwood correlation factor were determined using these fitting parameters for these solvent mixtures at various concentrations and temperatures. By using these dielectric parameters, the excess permittivity and excess inverse relaxation time is obtained. The excess permittivity is found to be positive for all concentrations and temperatures whereas the excess inverse relaxation time is negative.     

Sandwich-type transition metal complexes [(CBO)n]2M with carbon boronyl ligands (CBO)n (n=4–6)

A density functional theory investigation on a series of sandwich-type transition metal complexes [(CBO)_n]₂M (n=4–6; M=transition metals) with carbon boronyls (CBO)_n as effective aromatic ligands has been presented in this work at B3LYP level. The ground-states of these complexes possess staggered D_nd symmetries, while the corresponding eclipsed D_nh structures exist as transition states with slightly higher energies (within 5.8 kJ/mol). Carbon boronyl complexes [(CBO)_n]₂M are confirmed to be much more stable than their boron carbonyl isomers [(BCO)_n]₂M, which, on the other hand, take eclipsed ground-states with D_nh symmetries. The carbon boronyl complexes [(BCO)_n]₂M proposed in this work parallelize the well-known sandwich-type hydrocarbon complexes [C_nH_n]₂M in coordination chemistry with boronyl groups –BO isolobal to –H atoms in corresponding ligands.