Docking of An Asphaltene Molecular Model on A Fe2O3 Surface,An Ab Initio Simulated Annealing

Abstract

The docking of an asphaltene molecular model over the (1000) hematite surface is analyzed through the use of ab initio molecular dynamics simulation techniques where the Density Functional Theory (DFT) forces were obtained using the Harris functional approach. The (1000) hematite surface is modeled by a supercell slab lattice of 225 atoms with a  =  b lengths of 25.17 Å; on the c -direction an empty gap space and Fe-O-Fe-Fe-O atomic sequence was built. This structure was thermally stabilized at 400K. The asphaltene-hematite surface interaction was simulated with an annealing process at 400K during 555 fs, and then a geometry optimization process was carried out on the final annealed configuration in order to stabilize the asphaltene-surface system. We find an attractive interaction between the asphaltene and the Fe₂O₃ which is located mainly at the asphaltene aromatic region. Finally, we have obtained cohesion energy of ?417 kcal/mol, indicative of quimisorption energy on the basis of a Harris functional treatment.     

Submicron-Sized Gamma-HMX: II. Effect of Pressing on Phase Transition

In a previous article we described the preparation and initial characterization of a novel submicron-sized HMX (sm-HMX). Using Raman spectroscopy, the sm-HMX was found to be the gamma polymorph and to be stable with respect to conversion to beta-HMX under ambient conditions for at least a year. Pressing of sm-HMX powder in a small diameter pellet press at pressures from 10,000 to 31,000 psi and 1- to 5-min hold times was found to promote the gamma-to-beta polymorphic phase transition. The fraction converted and rate of conversion versus time after pellet removal from the press were found to fit a sigmoidal curve, indicating nucleation and growth as a possible polymorphic transition mechanism.     

DFT Molecular Dynamics Study of Pyrene Biradical Species

Abstract

The pyrene molecule shows its aromaticity localized in specific regions in the molecular framework as it is indicated by the calculated Nuclear Independent Chemical Shift (NICS) values, on previous electronic structure studies (García-Cruz et al. (2004) J. Phys. Chem. A 108, 5111 and Hernández-Trujillo et al. (2005) Chem. Phys. 308, 181), which is in full agreement with Clar's theory. The biradical formed at 400 K follows a simple mechanism, which yields an aromatic species as it is demonstrated by the NICS value. The analysis for testing the homolytic fragmentation and the unusual stabilization are also investigated. A possible implication of the reactivity of pyrene species in asphaltene formation is discussed.     

基于密度泛函理论的量子化学方法研究仪长管输油渣油中金属卟啉化合物

基于密度泛函理论(DFT)的量子化学计算方法,对仪长管输油渣油中几种含量最丰富的金属卟啉化合物进行分子模拟,并对其空间分子结构进行结构优化及计算,得到键参数、偶极矩以及电子吸收光谱等信息。通过分子的键参数和偶极矩发现,镍卟啉化合物的极性小于钒卟啉化合物,DPEP型卟啉分子的极性略大于ETIO型卟啉分子。计算了4种典型金属卟啉分子紫外吸收光谱的Soret吸收带和Q吸收带特征吸收峰,并得到4种卟啉化合物的稳定性由强到弱的顺序为ETIO型镍卟啉C₃₅-(ETIO-Ni)、DPEP型镍卟啉C₃₅-(DPEP-Ni)、ETIO型钒卟啉C₃₄-(ETIO-VO)、DPEP型钒卟啉C₃₁-(DPEP-VO)。     

碱度对杂原子介孔分子筛相转变的影响

在十六烷基三甲基溴化铵、正硅酸乙酯、氢氧化钠体系中添加不同铝源、钛源制备杂原子介孔MCM-48分子筛。通过调变母液的碱度,经水热晶化在不同杂原子源合成体系中按不同次序分别得到杂原子M41S系列的六方相(MCM-41)、立方相(MCM-48)和层状相(MCM-50)产物,其中立方相产物出现在较窄的碱度区间。合成过程中硅源正硅酸乙酯在不同碱度下的缩聚产物硅酸根多聚体或低聚体和水解产物乙醇的含量是生成立方相产物的关键因素,而杂原子源中的异丙醇会削弱碱度对产物相态的影响。在此相变规律基础上,对于不同杂原子源采用合适的母液碱度获得高杂原子含量的n(Si)∶n(Al)=20的Al-MCM-48分子筛和n(Si)∶n(Ti)=50的Ti-MCM-48分子筛。     

A Quantum Chemistry Study on Structural Properties of Petroleum Resin

The geometries of resins with single-layer (SG), double-layer (DG) and triple-layer (TG) were calculated with the quantum chemistry method. The geometries and net charges of atoms were obtained. The calculated average distances between layers were 0.5348 nm and 0.5051 nm and the action energies were -9.6355 kJ/mol and -32.2803 kJ/mol for resins DG and TG, respectively. Higher electronegative polar atoms can easily form hydrogen bonds with hydrogen atoms of other resin molecules, resulting in resin aggregates. The minimum cross-sectional diameters of resin molecules are too large to enter the pores of zeolite, so they are likely to crack on the surface of zeolite.     

A DFT-D Study on Structural,Electronic, Thermodynamic,and Mechanical Properties of HMX/MPNO Cocrystal under High Pressure

An investigation on the structural, electronic, thermodynamic, and mechanical properties of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX)/2-methylpyridine-N-oxide (MPNO) cocrystal was carried out from 0 to 100 GPa by using a dispersion-corrected density functional theory (DFT-D) method. Our calculated crystal structure is in excellent agreement with experimental results at ambient pressure. Based on the analysis of lattice parameters, lattice angles, bond lengths, bond angles, and dihedral angles under high pressure, we observe that HMX molecules in the cocrystal bulk are seriously distorted but MPNO molecules remain relatively unchanged. Hydrogen bond lengths are greatly shortened under high pressure. In addition, with the increase in pressure, the bandgap decreases gradually. However, it increases suddenly at 70 GPa. Some important hydrogen bonds between HMX and MPNO are also observed in the density of states spectrum. According to the thermodynamic analysis, this cocrystal is more easily prepared under low pressure. Finally, we characterized its mechanical properties and the results show that this cocrystal is malleable in nature. We expect that this research can provide a fundamental basis for further HMX cocrystal design and preparation.     

密度泛函理论研究Y分子筛的Bronsted酸性

利用密度泛函理论(DFT),研究了Y分子筛骨架上4种O—H(Bronsted酸位)的酸性,计算基于以B酸位为中心的团簇模型,采用BLYP方法。结果表明,通过计算Y分子筛的团簇结构、去质子化能量以及NH3,C5H5N在B酸中心上的吸附能,得出Y分子筛4种O—H的酸性由强至弱顺序为:SOD笼内的O 2 H、超笼内的O 4 H、超笼内的O 1 H/六棱柱内的O 3 H,即Y分子筛中最强的B酸位在SOD笼内。4种酸性中心与碱性探针分子之间的吸附稳定性由强至弱的顺序为O 4,O 1,O 2/O 3,分子筛的空间位阻致使吸附稳定性顺序与酸性顺序不同。探针分子通常倾向于与B酸位在超笼内吸附。     

A Theoretical Study on the Interaction of Crown Tetraalanylpeptide with NO3- and SO4/2-

Crown peptide is a kind of special conformation found on the homodetic cyclopeptide, regular array about the main chain containing imido groups, and the monolithic conformation presents coronary analogy to crown ether. There are high symmetrical ionophores belonging to Cn point group. The channels or apertures can form easily for recognizing certain ion or molecular, and also the function of intending dual-recognition and the ability for transporting as ionophores can be possessed. Under the method of density functional theory, the geometry structures, values energy and population analysis of the combo of crown tetraalanylpeptide （C4-Ala） with NO3- and SO4/2- are calculated, based on the foundation of former studies. Compared with the structure of C4-AIa without NO3- and SO4/2- it is found that the coronary shape changes little in the complex of C4-Ala-YOm/n-, and the electrons transfer between C4-AIa and YOm/n- at the mean time. There are hydrogen bond between oxygen of YOm/n- and the hydrogen from imine groups of C4-AIa, and they become weaker when the average charge density lessens.