Applications of the molecular orbital graph theory (XI)——The molecular moment's method of evaluating π-bond grade and judging relative reactivity of even AH

The tree graph method of evaluating the local molecular moment is proposed. By applying this method and the molecular moment formula of π-electron energy in the molecular orbital graph theory, a topological method of using the molecular moment to judge the relatively reactive point of even AH is achieved.     

A SOLUTION TO THE UPWARD MIGRATION OF AN INTRUSION

The evolution of the upward migration of the magma is a nonlinear and unstable problem in mathematics. It is difficult to solve it. And using the numerical method, the solution is relatively tedious and time-consuming. This paper introduces a method of the instantaneous point source to solve the linear and unstable heat conduction equation during the infinite period of time instead of the solution of the nonlinear and unstable heat conduction equation. The results obtained by this method coincide with those by the numerical method, meaning that this method offers a simple way to solve the nonlinear and unstable heat conduction equation.     

A theoretical form of the Martin-Hou equation of state

A new equation of state is derived from the Barker-Henderson hard-sphere perturbation theory. It has the form similar to the Martin-Hou equation of state. The numerical values of the characteristic constants in the equation can be calculated by the method of Martin and Hou. The equation can be used to predict P-V-T properties accurately for fluids when the critical parameters (T_c, P_c and V_c) and one point on the vapor pressure cure are given. By using the functional relationships between the characteristic constants and the microscopic parameters, the molecular microscopic parameters of the substance can be obtained.     

THE THEORETICAL STUDY OF THE TRANSITION STATE OF THE REACTION H_2C=N=N—■H_2 AND ITS REACTION PATH

By means of energy gradient, the optimized geometries of diazomethane, diazirine and the transitionstate of the unimolecular reaction are discussed on the ground potential energy surface calculated byMINDO/3 SCF method. The nine vibrational normal modes in the transition state and the reaction pathcalculated with Fukui's IRC equation are also studied. The symmetry of the C_s point group of thereaction system is conserved throughout the reaction path. The MO correlation diagram shows that thisunimolecular reaction is symmetry admitted.     

A method to fast determine the coupling coefficients in CI calculation

A new algorithm for evaluating the coupling coefficients and the addresses of molecular integrals in configuration interaction (CI) calculations is presented, which leads to an improved CI calculation program CGUGA. The validity and efficiency of the new code are compared with other programs, such as MELD and GAUSSIAN-94.     

Sample Duplication Method for Monte Carlo Simulation of Large Reaction-Diffusion System

The sample duplication method for the Monte Carlo simulation of large reaction-diffusion system is proposed in this paper. It is proved that the sample duplication method will effectively raise the efficiency and statistical precision of the simulation without changing the kinetic behaviour of the reaction-diffusion system and the critical condition for the bifurcation of the steady-states. The method has been applied to the simulation of spatial and time dissipative structure of Brusselator under the Dirichlet boundary condition. The results presented in this paper definitely show that the sample duplication method provides a very efficient way to sol-'e the master equation of large reaction-diffusion system. For the case of two-dimensional system, it is found that the computation time is reduced at least by a factor of two orders of magnitude compared to the algorithm reported in literature.     

Ab Initio Study on the Isomerization and Dehydrogenation of Methylnitrene

The ab initio calculations were performed at the RHF/4-31G level with the reaction pathways of the iso-merization and dehydrogenation of methylnitrene by the intrinsic reaction coordinate method. The results show that the transformation from methylnitrene to methylenimine would be very easy. This accountes for the experimental fact that one couldn' t find the methylnitrene, but only obtained the methylenimine in the pyrolysis of methyl azide. The mode-selective study reveals the reaction coordinates (IRC) of isomerization and dehydrogenation of methylnitrene are associated with the molecular deformation mode of 1191 cm-1 and the methyl group unsymmetrical stretch mode, respectively. The coupling between normal coordinates is favourable to select the reaction channel of isomerization.     

Ab initio studies on the thermolysis of azetidine

The reaction mechanism of the thermolysis of azetidine to form ethylene and methylen-imine has been studied by ab initio SCF MO method at STO--3G and 3-21G levels. Two possible step-wise pathways are explored. One is the breaking of C--C bond as the first step, while the other is thebreaking of C--N bond. All the stationary points on the potential energy surface (PES) are fully optimiz-ed. MP2 / 3-21G single point calculations on all stationary points and MCSCF / STO-3G computationsfor some stationary points are also carried out. The calculations indicate that azetidine decomposesvia biradicaloid intermediates and the cleavage of C--N bond is preferable to that of C--C bond.     

Description of the Structure and Properties of Atactic Polystyrene Melt Using Integral Equation Theory

The polymer reference interaction site model （PRISM） integral equation theory was used to describe the structure and thermodynamic properties of atactic polystyrene （aPS） melt, in which the monomer of aPS is represented with an eight-site model to characterize its microstructure. The intramolecular structure factors needed in the PRISM calculations were obtained from single chain MD simulations. The calculated results indicate that the results by the integral equation method agrees well with experiments, and can reflect the fine microscopic structure of real aPS melt. This work shows that the PRISM theory is a powerful tool for investigating the structure and properties of complex polymers.     

Correlation between hydrocarbon distribution and water-hydrocarbon ratio in Fischer-Tropsch synthesis

In order to shorten the evaluation cycle of cobalt catalyst before the optimized catalyst is fixed on, a mathematical method is proposed to calculate weight percentage of C5+ hydrocarbons. Based on the carbide polymerization mechanism and the main hydrocarbons being linear alkanes and α-olefins, the correlation between hydrocarbon distribution and the molecular mass ratio of water to hydrocarbons is discussed. The result shows the ratio was within the range of 1.125-1.286 and the lower the ratio, the more gaseous hydrocarbons were obtained. Moreover, a linear equation between the weight percentage of C5+ hydrocarbons and the weight ratio of C5+ hydrocarbons to the total water is established. These results are validated by corresponding experiments. The weight percentage of C5+ hydrocarbons could be immediately calculated by this linear equation without detailed gas chromatography (GC) analysis of them.     

Protonation effects on electron transport through diblock molecular junctions:A theoretical study

Diblock oligomers are widely used in molecular electronics. Based on fully self-consistent nonequilib-rium Green's function method and density functional theory, we study the electron transport properties of the molecular junction with a dipyrimidinyl-diphenyl (PMPH) diblock molecule sandwiched between two gold electrodes. Effects of different kinds of molecule-electrode anchoring geometry and protona-tion of the PMPH molecule are studied. Protonation leads to both conductance and rectification en-hancements. However, the experimentally observed rectifying direction inversion is not found in our calculation. The preferential current direction is always from the pyrimidinyl to the phenyl side. Our calculations indicate that the protonation of the molecular wire is not the only reason of the rectification inversion.     

Multi-segment linear gradient optimization strategy based on resolution map in HPLC

1 Introduction As a powerful tool of separating and analyzing complex samples, high performance liquid chroma- tography (HPLC) is widely applied. The key point of establishing stable and complete method of analysis is the selection of separation conditions. Accompanying the development of computer technology, it is possible to investigate the separation performance of each component in the sample under a wide range of ex- perimental conditions based on the information ob- tained by carrying …     

THE CONTROL OF POLYMETHACRYLATE MOLECULAR STRUCTURE BY GROUP TRANSFER POLYMERIZATION

INTRODUCTION Group transfer polymerization (GTP) is a method for controlling the structure of acrylic polymers in which reactive chain ends are covalentiy bound to a trimethylsilyl group. In the presence of a catalyst, monomer inserts into these chain ends between the silyl group and the last monomer unit. The process is illustrated by equation (1) for methyl methacrylate. GTP is a living polymerization, i. e., there is little or no chain termination and no chain transfer. A significant advantage of GTP is that it     

The Structure and Nonlinear Optical Properties of Octupolar Compound： 2, 4, 6－Tristyryl－s－triazine

The crystal of 2, 4, 6-tristyryl-s-triazine (TSTA) has been prepared and its crystal structure been determined to be in the polar non-centrosymmetric space group Cmc21. The molecular structure of TSTA is characterized by the slightly curved planar configuration and the octupolar C3v molecular symmetry. As exoected. TSTA crvstal shows a quite novel nonlinear optical (NLO) property with its powder second ha~onic generating(SHG) intensity of 1.8 times as that of urea. It also shows excellent transparency (with the peak position of 322 nm in absorption spectrum) and good thermal stability (with the melting point of 225-229℃).     

Formation Mechanism and Stability Study of Konjac Glucomannan Helical Structure

The formation mechanism and stability of konjac glucomannan (KGM) helical structure were investigated by molecular dynamic simulation and experimental method. The results indicate that the molecular conformation of KGM is a non-typical helical structure. In detail, helical structure of KGM is mainly sustained by acetyl group, whose size and stability are affected by the molecular polymerization degree of KGM. In vacuum among the non-bonding interactions, electrostatic force is the greatest factor affecting its helical structure, but in water solution, hydrogen bond affects the helical arrangement greatly. To our interest, temperature exhibits a reversible destroying effect to some extent; the helical structure will disappear completely and present a ruleless clew-like arrangement till 341 K. This work suggests that the method of combining molecular dynamic simulation and experiment tools can be effective in the study of KGM helical structure.     

On the Rotational Invariance of the INDO Method Including f Orbitals into the Basis Set

In order to ensure the rotational invariance of the one-center-two-electron integrals in the INDO method including f orbitals into the basis set in our previous paper two methods are proposed in the present investigation to meet this requirement.The first one is to use the weighted average values for replacing the integrals respectively.The second is a more stringent alternative,in which we have derived 690 nonzero hybrid one-center-two-electron integrals in addition to Coulomb and exchange types as expressions of Slater-Condon parameters.     

DSC Study on Brain Tubulin and the Effect of Cisplatin

Microtubules, a class of cytoskeletal elements, appear to be present in all eukaryoticcells. The temporal and spatial control of assembly and disassembly of microtubulesis believed to be a key factor in cellular function. Microtubules and their subunits(Q-0 tubulin heterodimers, MW 1 10,000) maintain a dynamic equilibrium in the cellcytoplasm. In addition, it is postulated that the lability of cytoplasmic microtubulescaused by drug is related to their equilibrium. Calorimetry method has been…