Does ionized diacetylene have a positive proton affinity?

Singly and doubly charged C₄H₃^+/2+ ions generated upon electron ionization (EI) of the neutral precursors 1,3-butadiene, benzene, and exo-methylene cyclopropane, respectively, are examined by sector-field mass-spectrometry. Charge stripping of the mass-selected monocations affords the corresponding dications and charge exchange of the C₄H₃²⁺ dications allows for the reverse redox process. Refined analysis and additional MS/MS studies suggest that the monocations are mixtures of isomeric ions formed upon ionization, whereas only a single type of dication seems to be formed. As an average of energy-resolved measurements, a vertical ionization energy of IE_v(C₄H₃⁺)=16.5±0.4 eV is derived. In addition to the experimental work, density functional theory is used for a computational exploration of the mono- and dicationic species. The best theoretical estimates are IE_a(C₄H₃⁺)=16.33 eV and IE_v(C₄H₃⁺)=16.49 eV for the most stable isomer H₂C=C---CCH⁺. Combination of the experimental and theoretical findings leads to the conclusion that the diacetylene cation C₄H₂⁺ has indeed a positive proton affinity of PA(C₄H₂⁺)=1.50±0.42 eV.     

用密度泛函理论研究Lennard-Jones 流体在狭缝中的相平衡

用改进的基础度量理论(modified fundamental measure theory, MFMT)和密度Taylor展开分别表达过剩自由能中的短程作用和色散作用. 流体分子与狭缝壁之间的相互作用以10-4-3势能函数表达. 由巨势最小原理确定Lennard-Jones (LJ)流体在狭缝中的密度分布和过剩吸附量, 所得结果与分子模拟数据吻合良好. 根据平衡时两相温度, 化学势及巨势相等, 计算了LJ流体在狭缝中的相平衡.     

The role of C-centered radicals on the mechanism of action of artemisinin

Artemisinin is a sesquiterpene lactone with an endoperoxide function that is essential for its antimalarial activity. Endoperoxides are supposed to act on heme leading to the reduction of the peroxide bond and production of radicals, which can be responsible for killing the parasite. The geometries of artemisinin, radical anions and neutral species generated by rearrangement after reduction of the peroxide bond were fully optimized with the AM1 and PM3 semi-empirical methods, in order to characterize the intermediates formed during the process. Among the radicals calculated along the pathway for reductive decomposition of artemisinin, the secondary radical centered on carbon C₄ has the highest stability when compared to other radicals that can be achieved either by hydrogen migration to the original O-centered radical or by homolytic break of C–C bond. This suggests that the C₄-centered radical may be the species responsible for killing the parasite, as has been indicated previously in experimental studies.     

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.     

Fitting complex potential energy surfaces to simple model potentials: application of the simplex-annealing method

A stochastic method of optimization, which combines simulated annealing with simplex, is implemented to fit the parameters of a simple model potential. The main characteristic of the method is that it explores the whole space of the parameters of the model potential, and therefore it is very efficient in locating the global minimum of the cost function, in addition to being independent of the initial guess of the parameters. The method is employed to fit the complex intermolecular potential energy surface of the dimer of water, using as a reference the spectroscopic quality anisotropic site-site potential of Feller et al. The simple model potential chosen for its reparameterization is the MCY model potential of Clementi et al. The quality of the fit is assessed by comparing the geometry of the minimum, the harmonic frequencies, and the second virial coefficients of the parameterized potential with the reference one. Finally, to prove more rigorously the robustness of this method, it is compared with standard nonstochastic methods of optimization.     

Vibrational analysis of 3-trifluoromethylphenol

The molecular geometry and molecular vibrations of 3-trifluoromethylphenol have been investigated by means of quantum chemical calculations and vibrational spectroscopy. The computations indicated the preference of the conformer with the OH hydrogen pointing in the direction of the trifluoromethyl group by 0.9 kJ/mol with respect to the anti conformer. FT-IR spectra of the vapour and CCl₄ solution as well as FT-IR and FT-Raman spectra of the pure liquid have been recorded in the range of 4000–150 cm⁻¹. The interpretation of the spectra was based on a scaled quantum mechanical (SQM) analysis for which the initial force field was calculated at the Becke3-Lee-Yang-Parr (B3LYP) DFT level supplemented with a 6-311++G** basis set. Using 11 scale factors refined in the present study an rms deviation of 7.6 cm⁻¹ between the experimental and SQM frequencies has been achieved. On the basis of the computations 40 of the total of 42 fundamentals of the title compound have been assigned.     

Conduction stability of high-density polyethylene/carbon black composites due to electric field action

Conduction stability of high-density polyethylene/carbon black (HDPE/CB) composites with a CB volume fraction slightly above the percolation threshold is studied in relation to electric field action at various ambient temperatures below the melting point of HDPE. It is found that resistance of the composites shows considerable changes after the electric field is switched off. Influence of irradiation crosslinking of HDPE on the conduction stability is also discussed.     

Approximate transferability in alkanenitriles

The atomic and bond properties of a series of alkanenitriles were calculated in order to analyze the transferability of the CN, methyl, and methylene groups. The calculations were carried out using the atoms in molecules (AIM) theory on RHF/6‐31++G**// RHF/6‐31G** wave functions obtained for compounds CN–R (R ranging from H to C₁₁H₂₃). Linear correlations between L(Ω) and N(Ω) were used to establish N(CH₂) and N(CH₃) nearly transferable values. Average values and maximum differences to the mean value of several properties were used for classifying the CN group. It shows a transferable behavior along the CN–R series for R>Et. The methyl group presents specific properties when R<Pr. The methylene groups can be classified considering both their position with respect to the end of the chain and the position with respect to the CN group. The atomic energy displays a dependence on the molecular size. Although this behavior does not allow to consider this property as transferable, both the ab initio total electronic molecular energies and the experimental heats of formation can be fitted, by linear regression analysis, as a function of the number of methylene groups. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Zr（Ⅳ）／PVA功能膜的膜催化酯化反应研究

在催化与渗透汽化分离技术相偶合的渗透汽化型膜反应器中，研究了羧酸酯的液相合成反应．实验中制备了两类具有强酸催化活性的ｚｒ（Ⅳ）／ＰＶＡ（聚乙烯醇）功能膜，采用管式膜方式，以乙酸正丁酯的合成反应为探针，对这类新型的催化反应技术在催化活性、分离性能以及分离对反应转化的影响等方面进行了探索性研究。从得到的结果看，膜催化酯化反应过程的反应条件和缓，转化率可达到９８％，反应的选择性为１００％．