生物活性物质大豆苷元的量子化学研究

采用PM3-MO方法，对大豆苷元进行了量子化学计算，给出了分子轨道及其能级、电荷密度、键长、二面角参数等。结果表明：大豆苷元分子中苯并吡喃环（A环和C环）带较强的正电荷，易与受体的负电荷中心结合；B环是负电子区域，易与受体的正电荷中心结合；其他部分通过氢键与受体发生作用，从而发挥生物活性。     

丹皮酚缩乙二胺席夫碱还原产物的合成及量化计算研究

以丹皮酚和乙二胺为原料合成席夫碱，经硼氢化钠还原得标题化合物，收率为67.2％；通过元素分析以及红外波谱对标题化合物进行表征。使用Hyperchem7.0程序，用半经验方法计算了化合物分子中能量分布、主要键长、键角以及主要原子的净电荷分布。计算结果分析表明，分子中主要原子之间的键长、键角基本在正常的范围内；负电荷主要集中于氧原子和氮原子上，分子呈现最优化的结构并具体一定的稳定性。     

一种计算H_3分子键长、键能的新方法

本文用宏观方法考察平面三角形H_3分子,推导出氢原子半径与平面三角形H_3分子的键长Re的方程式,计算得到H_3分子的键长■,然后通过平均电势能密度理论计算氢分子键能的方法推广至平面三角形H_3分子,假定平面三角形H_3分子键和的微观机理为三个氢原子结合成H_3分子后平均电势能密度相等,获得了H_3分子键长、键能与氢原子半径之间的理论方程式。计算了H_3分子的键能进行,键能De=-3.825 eV,理论计算值与实验值较好的吻合。理论模型简单直观,物理意义清晰明确,计算方法极为简单且计算中不含任何人为性的参数。     

去氢枞酸甲酯选择性硝化反应的研究

采用均匀设计方法深入研究了去氢枞酸甲酯在HNO3-Ac2O-AcOH体系中选择性硝化的反应条件.通过理论计算和实验验证获得去氢枞酸甲酯选择性硝化的较优反应条件如下:n(硝酸):n(去氢枞酸甲酯)为3:1、混合溶剂中乙酐与乙酸的体积比为7:1、反应温度为20℃、反应时间为60 min.此时12-硝基去氢枞酸甲酯和14-硝基去氢枞酸甲酯的总产率由50%提高到84.6%,其中12-硝基去氢枞酸甲酯的产率达到64.0%、14-硝基去氢枞酸甲酯的产率达到20.6%,二者的产率比约为3.1:1.12-硝基去氢枞酸甲酯的反应产率和选择性都明显高于文献报道值.     

过氧化麦角甾醇分子的密度泛函理论研究

采用密度泛函理论(DFT)方法,在B3LYP/6-311+G(2d,p)水平上对过氧化麦角甾醇进行了计算研究。优化得到了过氧化麦角甾醇分子的结构,给出了分子的键长、键角、二面角等参数,并对其进行了1HNMR光谱、IR光谱、UV-Vis光谱理论模拟和自然电荷分析。自然电荷计算表明,羟基O和H原子很可能是关键的活性中心。理论计算结果与实验值符合的很好。     

环氧丁二酸的结构和性质的理论研究

采用Materials Studio中的Dmol3程序对环氧丁二酸的结构和相关性质(键角键长、Mulliken电荷、振动强度、热力学性质、分子得失电子能力和稳定性)进行了理论性研究。通过Dmol3中的geometry optimization计算出各原子的电荷、振动频率等性质。计算结果明环氧丁二酸分子容易得到电子,并且环氧基上氧原子是与其它物质亲电反应的作点。     

CO在Cu(100)表面最佳吸附位研究

采用密度泛函理论(DFT)对CO分子在Cu(100)表面上的吸附行为进行了研究。计算结果表明：顶位吸附和桥位吸附这两种模型中CO分子都倾斜地吸附在Cu原子上，其中顶位吸附的C-0键长(0．1155nm)和Cu—C键长(0．1840nm)与实验值符合得很好，而且C-O键长均比自由CO分子的C-O键长要长。说明Cu原子活化了CO分子。另外，顶位吸附时的体系能量较低，且有较大的吸附能，说明顶位吸附模型更稳定，所以CO很可能采用顶位吸附模型。从Mulliken轨道分布数据可以看出Cu原子上的σ电子向Cu原子的4p轨道和O原子的2p轨道转移，从而CO分子上的电子云会发生重排，组成新的轨道，所以CuCO就会形成弯曲结构。     

杂环轮烯类化合物密度泛函理论研究

运用量子化学中的密度泛函和含时密度泛函理论法,计算了四种加共轭环的脱氢苯[15]轮烯衍生物的几何构型、电子结构、前线分子轨道和电子光谱性质。计算结果表明当脱氢苯[15]轮烯分子(M)被杂环取代或增加分子的共轭性,对轮烯的键长和键角等结构参数的影响不大,这与轮烯具有较强的共轭性有关。当母体中的苯环被嘧啶环取代时,最大吸收波长蓝移;当母体中的苯环被萘取代时,最大吸收波长与母体中的苯被吡嗪取代时的最大吸收波长相近。     

二苯二硫醚的结构和性质的理论研究

采用Materials Studio中的Dmol3程序对二苯二硫醚的结构和相关性质(键角键长、Mulliken电荷、振动强度、热力学性质、分子得失电子能力和稳定性)进行了理论性研究。通过Dmol3中的geometry optimization计算出各原子的电荷、振动频率等性质。计算结果明二苯二硫醚分子容易得到电子,并且两个硫原子可能是与其它物质亲电反应的作点。     

对苯二酚成键特性及半醌稳定性的量子化学研究

采用B3LYP方法和6-311 G(3df,2P)基组,通过密度泛函理论(DFT),对对苯二酚结构进行了优化,并分别计算了原子间键长、键角、单点能和Mullikin电荷分布.结合自然键(NB0)理论分析其成键特性.并对其产生的半醌自由基的稳定性进行了量化研究.     

Corrosion inhibition of carbon steel in hydrochloric acid by furan derivatives

The efficiency of three furan derivatives (2-methylfuran, furfuryl alcohol and furfurylamine), as corrosion inhibitors for carbon steel in 1 M HCl, has been determined by gravimetric and electrochemical measurements. These compounds inhibit corrosion even at very low concentrations, and furfuryl alcohol is the best inhibitor. Polarization curves indicate that all compounds are mixed inhibitors, affecting both cathodic and anodic corrosion currents. Adsorption of furan derivatives on the carbon steel surface is in agreement with the Langmuir adsorption isotherm model, and the calculated Gibbs free energy values confirm the chemical nature of the adsorption. The structural and electronic properties of these inhibitors, obtained using AM1, PM3, MNDO and MINDO/3 semi-empirical self-consistence field methods, are correlated with their experimental efficiencies.     

AM1, MNDO AND MINDO/3 TREATMENTS OF HÜCKEL TYPE CYCLACENES

Hückel type cyclacenes having R = 3–10 have been subjected to quantum chemical analyses at the level of AM1, MNDO and MINDO/3 (UHF and RHF) type semi-empirical treatments. The structures have been found to be stable but endothermic in nature. No cryptoannulenic effect has been observed when AM1 (UHF) and MNDO (UHF) treatments are used. Whereas MINDO/3 (UHF) and all the RHF type calculations indicated certain degree of cryptoannulenic effect R = 4 through 8 for the heat of formation values. Frontier molecular orbital energies of the systems have also been reported.     

Molecular dynamics simulations of deformation mechanisms of amorphous polyethylene

Molecular dynamics simulations were used to study deformation mechanisms during uniaxial tensile deformation of an amorphous polyethylene polymer. The stress-strain behavior comprised elastic, yield, strain softening and strain hardening regions that were qualitatively in agreement with previous simulations and experimental results. The chain lengths, number of chains, strain rate and temperature dependence of the stress-strain behavior was investigated. The energy contributions from the united atom potential were calculated as a function of strain to help elucidate the inherent deformation mechanisms within the elastic, yield, and strain hardening regions. The results of examining the partitioning of energy show that the elastic and yield regions were mainly dominated by interchain non-bonded interactions whereas strain hardening regions were mainly dominated by intra-chain dihedral motion of polyethylene. Additional results show how internal mechanisms associated with bond length, bond angle, dihedral distributions, change of free volume and chain entanglements evolve with increasing deformation.     

偏二甲肼分子化学键解离能的理论计算

利用量子化学组合从头算方法和密度泛函理论方法计算了偏二甲肼分子的准确化学键解离能。结果表明,除N—C键外,组合从头算方法对该分子其余键解离能的计算值与文献值都很接近;密度泛函理论中BMK方法的计算结果与组合从头算方法的结果很接近,对于N—H和C—H键,B3P86方法的计算结果稍优于BMK方法,而B3LYP方法则普遍低估了键解离能。由于自旋污染的原因,限制性开壳层方法要优于非限制性方法。计算结果表明,偏二甲肼分子中N—N和N—C键的键解离能最低。     

Dimeric components from the dimerization of abietic acid

Capillary gas-liquid chromatography of the product formed by sulfuric acid-catalyzed dimerization of abietic acid showed the presence of some 40 dimeric components. The three major components were isolated and shown to be heptacyclic dimers, two of which had a conjugated double bond system. The other component had two nonconjugated double bonds. Also isolated were three dimers consisting of monomers attached through a single carbon-carbon bond: one carboxyl group in each of these dimers was in the form of a γ-lactone. Maintained in cooperation with the University of Wisconsin.     

半晶态聚乙烯变形机理的分子动力学模拟

采用相间蒙特卡罗方法,建立半晶态聚乙烯模型。在温度350 K,x、y方向压力为0.1 MPa下进行拉伸,探究聚乙烯的拉伸机理和拉伸过程中微观结构的变化。在拉伸过程中,在弹性变形阶段,键长随着应变的增加而增加,键角和二面角也有少量的增加,且键长率先增长。过了屈服极限后,键长、键角和二面角不再增加,有一定量的减小,然后逐渐趋于稳定。变形区域主要发生在非晶区,拉伸时,分子链会发生取向,随着拉伸的进行,分子链发生滑移,最后会出现空穴现象。     

Corrosion inhibitors : Part II: Quantum chemical studies on the corrosion inhibitions of steel in acidic medium by some triazole, oxadiazole and thiadiazole derivatives

The corrosion inhibition efficiencies of some triazole, oxadiazole and thiadiazole derivatives for steel in presence of acidic medium have been studied by using AM1, PM3, MINDO/3 and MNDO semi-empirical SCF molecular orbital methods. Geometric structures, total negative charge on the molecule (TNC), highest occupied molecular energy level (E_HOMO), lowest unoccupied molecular energy level (E_LUMO), core-core repulsion (CCR), dipole moment (μ) and linear solvation energy terms, molecular volume (V_i) and dipolar-polarization (π^*), were correlated to corrosion inhibition efficiency. Four equations were proposed to calculate corrosion inhibition efficiency. The agreement with the experimental data was found to be satisfactory; the standard deviations between the calculated and experimental results ranged between ±0.03 and ±4.18. The inhibition efficiency was closely related to orbital energies (E_HOMO and E_LUMO) and μ. The correlation between quantum parameters and experimental inhibition efficiency has been validated by single point calculations for the semi-empirical AM1 structures using B3LYP/6-31G^** as a higher level of theory. The proposed equations were applied to predict the corrosion inhibition efficiency of some related structures to select molecules of possible activity from a presumable library of compounds.     

Nano-SiO<Subscript><Emphasis Type="Bold">2</Emphasis></Subscript>: An Efficient Catalyst for the Synthesis of Some new Benzimidazoles - NMR Spectral Characterization

Some benzimidazoles were designed and synthesized by a new route using nano-SiO₂ as a highly efficient catalyst. Synthesized compounds were characterized by ¹H and ¹³C-NMR spectral studies. The significant features of this nanocatalyst are high yield of products, short reaction times, green reaction media and a vast range of substrates usage. Proton and ¹³C chemical shift of the synthesized compounds were calculated. To further confirm the compound formation single crystal XRD analysis was made and discussed for 2-(1H-benzimidazol-2-yl) phenol (1). The crystal packing features four π– π stacking interactions involving the imidazole ring, fused benzene ring and attached benzene ring system [centroid–centroid distances = 3.6106 (17), 3.6108 (17), 3.6666 (17) and 3.6668 (17) Å]. Optimization of compound 1 was performed by DFT at B3LYP/6-31G (d, p) using Gaussian-03. All these XRD data are in good agreement with the theoretical values. However, from the theoretical values it is found that most of the optimized bond lengths, bond angles and dihedral angles are slightly higher than the XRD values.     

Structural Parameters of Photochromic Dihydroindolizines. X-ray Analysis and MINDO/3-Calculations

To elucidate the detailed geometry as well as the bonding situation in the new photochromic spirodihydroindolizines 3 an X-ray structure analysis of 3a, an analogue of 3, as well as MINDO/3-calculations for 4, a model for 3, were carried out. There is good agreement between the geometric data obtained by these two methods. The spiro bonds are long, due to spiro linking. The lengths of these bonds cannot be explained by spiro interactions, according to MINDO/3. They result, rather, from an increase of strain due to spiro linking. The longest of these bonds is the C(1)-C(4) one, which is about 0.01-0.20 Å longer than a normal C-C single bond. This is due also to the neighbouring sp³-hybridized N-atom. The C(1)-C(4) bond is therefore the weakest bond in the molecule, and can be broken very easily by UV or visible light, thus explaining the photochromic behaviour of this type of system.     

四乙酰基二硝基六氮杂异伍兹烷分子结构研究

四乙酰基二硝基六氮杂异伍兹烷(TADNIW)是合成六硝基六氮杂异伍兹烷(HNIW)的中间体。该文用Gaussian 98软件包,采用密度泛函理论B3LYP和标准基组6-31G对所选构型进行了全优化计算,在结构上对TADNIW的键长、键角、二面角、Mu lliken电荷及集居数进行了理论分析,发现笼形化合物的六元环成船式构象,硝基处于桥头,骨架以亚稳态存在。结构分析表明,六元环上N—NO2键相对较稳定,采用一般的硝解条件反应不能进行,作者提出了新的反应机理,即水解-硝化假设:含有酰胺基团的一类化合物在含水的硝化介质中首先发生水解生成相应的仲胺,碱性较强的仲胺再在氮硝化催化剂的作用下,迅速硝化成硝胺。计算得到TADNIW分子总能量为-1 583.375 682 a.u.,前线轨道能量差ΔE(ELUMO-EHOMO)为4.123 eV。计算IR谱图与实验IR谱图对比,误差小于20 cm-1。