蛋白质分子三维结构能量优化途径的选择

NMR方法是研究溶液中蛋白质的三维结构的重要手段,本文以BUSH ⅡA为例,对用度量矩阵距离几何法获得的初始三维结构进行了能量优化,主要探讨了蛋白质分子三维结构能量优化途径的选择问题.本文把优化过程分为三个阶段,分别采用不同的优化方式,使分子结构得到优化,对于分子量在8000左右的蛋白质而言,本方法能够获得较好符合核磁实验约束条件的分子低能构象.     

The incoherent Raman spectrum of O2 molecular constants from all experimental data

A new incoherent vibration-rotational Raman spectrum of ¹⁶O₂ recorded by means of an interferometer is presented. The measured wavenumbers are analyzed together with a coherent Raman spectrum, six different microwave spectra from the vibrational ground state, and one microwave spectrum from the first vibrationally excited state in one fit. Due to the non-linear energy expression for oxygen, such an analysis requires the use of an iteration to find the minimum for the so-called merit function. A method has been developed to secure a stable iteration. The energy expression originally contains 21 constants. A systematic search leads to a reduction of this to 19 constants to make the fit possible. This results in two solutions, which are, however, only two different ways of indicating the one final energy function. The systematic use of iterations reduces the influence of the computational uncertainty on the final molecular constants to be orders of magnitude lower than the uncertainty due to the experimental errors.     

基态和激发态氧振动光谱的量子力学计算

利用分子势能函数的Murrell-Sorbie和PG函数形式,将时域有限差分法应用基态和激发态氧分子的振动能级的量子力学计算,计算结果令人满意.     

The excess molar volumes of (hydrocarbon + branched chain ether) systems at 298.15 K and 308.15 K, and the application of PFP theory

The excess molar volumes, V_m^E, have been calculated from measured density values over the whole composition range at the temperatures 298.15 K and 308.15 K and under atmospheric pressure for the 12 mixtures {hydrocarbon (heptane, 2,2,4-trimethylpentane, 1-heptene or toluene) + branched chain ether (methyl 1,1-dimethylethyl ether, ethyl 1,1-dimethylethyl ether or methyl 1,1-dimethylpropyl ether)}. The excess volumes of all the mixtures except (toluene + ether) are positive over the whole composition range. The experimental results have been correlated and compared with the results from Prigogine-Flory-Patterson (PFP) theory.     

Fast intramolecular dynamics of triphenyl phosphite investigated by <Emphasis Type="Bold">2</Emphasis>H NMR

The first analysis of rapid intramolecular motions of triphenyl phosphite by ²H NMR is presented. The fragile slowing down of the primary relaxation is followed by a solid-echo method. The occurrence of a fast reorientation of the phenyl side groups is demonstrated in the supercooled liquid state, identified as a two-fold flip on the basis of simple lineshape simulations. Coexistence of both static and motionally averaged components in “two phase” spectra indicate a broad distribution of correlation times for this relaxation. This dynamical behavior is shown to persist in the glacial phase. Received 28 May 2002 / Received in final form 1st October 2002 Published online 31 December 2002     

Reaction Dynamics of Aligned Molecules

Photofragmentation—also termed ‘half collision’—is a method to comprehend the complicated process of a chemical reaction (the ‘full collision’) better. The use of polarized light enabled the study of the spectroscopy of aligned molecules, yielding information about the photochemically produced intermediate state—the transition state. Even though stable reaction products were studied, the forces responsible for the motions of the fragments can be visualized. In this way a model can be constructed that represents the part of the potential hypersurface responsible for the observed motions. The application of this spectroscopic method to hydrogen peroxide H₂O₂ has become a classic example. The complex decomposition of hydrazoic acid, HN₃, represented a challenge, and its successful solution proves the general applicability of this method.     

Investigation of the local structure variance of water molecules in laser-induced thermal desorption process

This paper presents the use of molecular dynamics simulation in the study of laser-induced thermal desorption (LITD) of water molecules adjacent to a laser-heated Au substrate. The local structure of the water molecules is investigated by considering the densities of the oxygen and hydrogen atoms, the average number of neighbors, n_NN, and the average number of H-bonds, n_HB. At an equilibrium temperature of 300 K, the simulation results show that three adsorption water layers are formed in the immediate vicinity of the Au surface, and that each four-fold hollow site on the uppermost Au(0 0 1) surface is occupied by a single water molecule. Following laser-induced heating of the Au substrate with a sub-picosecond laser pulse of 350 fs, the substrate temperature increases to 1000 K. This causes a gradual heating of the adjacent water film, which is accompanied by a decrease in the values of n_NN and n_HB. Hence, it can be concluded that an increase in the water film temperature destroys the hydrogen-bonding network throughout the water film. Although the maximum local temperature of the water film occurs in the region immediately adjacent to the Au substrate, it is determined that the attractive energy between the Au atoms and the water molecules in this region causes the water molecules to aggregate together to form three-dimensional water clusters. Furthermore, this energy prevents the hydrogen bonds in this region from breaking apart as violently as those within the phase explosion region. Finally, it is observed that the phase explosion phenomenon occurs in the region of the water film where the values of n_NN and n_HB are at a minimum.     

Magnesium chloride modified with organoaluminium compounds as a support of the zirconocene catalyst for ethylene polymerisation

This work describes the influence of the modification of the MgCl₂(THF)₂ and MgCl₂ magnesium supports with the AlEt₂Cl, MAO, AlEt₃, AlMe₃, and AlEt₂Cl alkylaluminium compounds on heterogenisation of the bis(cyclopentadienyl) zirconium(IV) dichloride Cp₂ZrCl₂ catalyst. It was found that only the MgCl₂(THF)₂ support modified with AlEt₂Cl gave the heterogeneous catalyst. On the contrary, application of a magnesium carrier modified by AlEt₃, AlMe₃, and MAO compounds only results in a homogeneous zirconocene catalyst.     

红辉沸石合成A型分子筛的红外光谱研究

以天然红辉沸石合成了A型分子筛，通过XRD、IR光谱研究了其晶化过程。发现在1000-950cm^-1、750一600cm^-1、560cm^-1、460cm^-1处的红外吸收峰随结晶度有规律的变化，初步探讨其反应机理。     

Evolutionary Prisoner's Dilemma on heterogeneous Newman-Watts small-world network

We focus on the heterogeneity of social networks and its role to the emergence of prevailing cooperators and sustainable cooperation. The social networks are representative of the interaction relationships between players and their encounters in each round of games. We study an evolutionary Prisoner's Dilemma game on a variant of Newman-Watts small-world network, whose heterogeneity can be tuned by a parameter. It is found that optimal cooperation level exists at some intermediate topological heterogeneity for different temptations to defect. That is, frequency of cooperators peaks at a certain specific value of degree heterogeneity — neither the most heterogeneous case nor the most homogeneous one would favor the cooperators. Besides, the average degree of networks and the adopted update rule also affect the cooperation level.