三硝基苯-对位取代苯酚负离子荷移复合物从头算研究

运用G94W量子化学程序,在HF/3-21G基组水平上对三硝基苯-对位取代苯酚(取代基:CH~3O-,CH~3-,Cl-)负离子的电荷转移复合物进行从头计算。把电荷转移复合物看成一个超分子,研究该系列复合物的稳定性、电荷转移及几何构型等规律。计算结果表明,苯酚负离子供电中心O沿一倾角指向三硝基苯中的任意相邻两个硝基之间的C位置上,复合物的稳定性按对位取代苯酚取代基CH~3O-,CH~3-,Cl-的次序减小,与实验规律相一致。计算结果还表明,形成该系列复合物具有明显的电荷转移,其稳定性与电荷转移量有关等。     

HCCO自由基与水分子氢键复合物的从头算研究

在MP2/aug-cc-pvdz水平下,对二体氢键复合物H2O…HCCO(Ⅰ)和HCCO…H2O(Ⅱ)以及三体氢键复合物(H2O)2…HCCO(Ⅲ),H2O…H2O…HCCO(Ⅳ)和H2O…HCCO…H2O(Ⅴ)的几何和相互作用能进行了计算.轨道分析表明Ⅲ中HCCO中的H(1),C(2)通过2个氢键与2个水分子形成了环...     

NH3…H2O体系氢键团簇结构的从头计算方案比较

对H2O，NH3单分子以及反式线性NH3…H2O双分子团簇应用HF，DFT，MR2，CCD ，QCISD等从头计算方法在不同的基组水平上进行几何结构优化和氨—水分子间相 互作用能计算。比较实验值和计算结果表明：对氨—水体系，MP2／6-31+G^**方法 能够满足氢键N-0键长误差为0．004nm，键角∠NOH误差为1°，NH3…H2O相互作用 能△E与CCD和QCISD偏差2．1kJ／mol计算精度的要求，并有较合理的计算代价。     

含酰胺和尿嘧啶的氢键复合物的三体效应

采用包含BSSE校正的MP2/aug-cc-pVTZ方法对酰胺、二肽、尿嘧啶和水分子形成的氢键复合物的三体效应进行了研究,分析了三体作用能对体系总作用能的贡献.结果表明,在这些氢键复合物中,三体作用能占体系总作用能的10%~20%,三体作用属于近程作用,因此在分子模拟中至少应考虑近处的三体效应.     

PH~3...H~2O体系分子间相互作用的从头计算MO研究

在MP2/6-311++G(3d,3p)水平,对PH~3...H~2O体系可能存在的氢键复合物进行了全自由度能量梯度优化,发现PH~3...H~2O体系存在三个能量极小结构A,B和C。其中结构A和B以H~2O作为质子授体,结构C以PH~3作为质子授体,结构A较结构B和C分别稳定6.52kJ/mol和8.18kJ/mol。结构A具有C~s对称性,其结构中P原子和O原子间距离为354.78nm,键角OHP为171.35ⅲ,属于接近于直线的传统型氢键结构。进一步在高级电子相关校正的MP4SDTQ下,用6-311++G(3df,3pd)基加上键函数{3s3p2d1f},通过BSSE校正,精确计算了结构A的结合能为-10.84kJ/mol。     

一系列氢键诱导液晶复合物的合成及表征

以２－氰基－３－（４－（２－氯－３－甲基－１－丁酰氧基）－苯基丙烯酸（Ａ）为质子给体，Ｎ－（４－吡啶基亚甲基）－４－烷氧基苯胺（ｎＳＳＺ）为质子受体，合成了一系列新的氢键复和物，经红外光谱证实了分子间氢键的存在，通过ＤＳＣ，偏光方法及Ｘ射线衍射方法对其液晶行为进行研究，结果表明复合物呈现近晶相行为。     

NH2 + HNCO反应机理的从头计算

在6-311G(d,p)基组水平上, 采用全电子的UMP2和UQCISD(T)方法对自由基NH₂和HNCO反应机理进行了研究, 结果表明, 反应存在如下两条反应通道: NH₂ + HNCO→NH₃ + NCO (1)和NH₂ + HNCO→N₂H₃ + CO (2). 反应(1)是吸氢反应, QCISD(T,full)// MP2(full)/6-311G(d,p) 计算位垒是29.04 kJ/mol. 与实验估计值29.09 kJ/mol一致. 在反应的温度区间(2300～2700 K),传统过渡态理论得出的速率常数值的范～围是1.68×1011～3.29×10¹¹cm³·mol^-1·s^-1, 支持了反应速率常数应小于等于5.0×10¹¹cm³·mol^-1·s^-1的实验结论. 对反应(1), 理论研究还得出反应物分子可通过分子间作用生成氢键复合物(HBC), 其能量相对于反应物降低32.41 kJ/mol. 反应(2)是一个可经过顺式或反式方式进行的分步反应, 在反应分子间第1步生成N—N键, 再经过一个C—N键断裂过渡态生成产物. 反应(2)控速步骤的位垒为92.79 kJ/mol(顺式)或147.43 kJ/mol(反式). 反应(2)位垒高于反应(1).     

氢键复合物自组装性质的研究

超分子复合物体系因近年来发展较快及应用范围广而颇具吸引力。作为形成超分子复合物的主要手段,氢键自组装对于高分子聚合材料以及生命科学等领域有着重要的意义。本文根据氢键的多重性及不同氢键的缔合方式对氢键复合物进行分类,并对氢键自组装复合物的性质和研究状况作了综述,同时介绍了本研究组在此方面的理论研究工作。     

取代基对1-甲基尿嘧啶与N-甲基乙酰胺氢键复合物中氢键强度的影响

使用密度泛函理论B3LYP方法和二阶微扰理论MP2方法对由1-甲基尿嘧啶与N-甲基乙酰胺所形成的氢键复合物中的氢键强度进行了理论研究, 探讨了不同取代基取代氢键受体分子1-甲基尿嘧啶中的氢原子对氢键强度的影响和氢键的协同性. 研究表明: 供电子取代基使N－H…O＝C氢键键长r(H…O)缩短, 氢键强度增强; 吸电子取代基使N－H…O＝C氢键键长r(H…O)伸长, 氢键强度减弱. 自然键轨道(NBO)分析表明: 供电子基团使参与形成氢键的氢原子的正电荷增加, 使氧原子的负电荷增加, 使质子供体和受体分子间的电荷转移量增多; 吸电子基团则相反. 供电子基团使N－H…O＝C氢键中氧原子的孤对电子轨道n(O)对N－H的反键轨道σ^*(N－H)的二阶相互作用稳定化能增强, 吸电子基团使这种二阶相互作用稳定化能减弱. 取代基对与其相近的N－H…O＝C氢键影响更大.     

Ab initio HF-SCF study of naphthazarin: Geometries,isomerism, hydrogen bonding,and vibrational spectrum

The structural properties and intramolecular hydrogen bonding of a series of structures of naphthazarin molecule were investigated by ab initio HF-SCF methods. The geometries of theC _2v ,C _2h ,D _2h , andC _s symmetry structures were optimized using split-valence basis sets. MP2/6-31G^*// HF/6-31G single-point energy calculations indicate that theC _2v isomer (5,8-dihydroxy-1,4-naphthoquinone) is the lowest energy structure of the molecule and that theC _2h symmetry one (4,8-dihydroxy-1,5-naphthoquinone), lying 37 kJ/mol above theC _2v form, is the other stable isomer of naphthazarin. At the HF/6-31G level, the intramolecular proton exchange between two equivalentC _2v structures is a two-step process where each proton can be independently transferred through an unsymmetrical potential having a 1,5-quinone intermediate, theC _2h symmetry structure, and two equivalent transition states ofC _s symmetry, with a barrier height equal to 38 kJ/ mol (MP2/6-31G^*//HF/6-31G). The study of naphthazarin molecule is flanked by a theoretical investigation on theC _2v andC _2h isomers of the parent naphthoquinone and dihydroxynaphthalene molecules. The SCF vibrational spectrum of the ground state of naphthazarin, harmonic frequencies, and infrared and Raman band intensities were computed at the HF/6-31G level. The results of the calculations are compared with the matrix isolation FT-IR spectroscopy measurements and with the infrared and Raman spectra of the crystal molecule.     

Ab initio calculations on halogen-bonded complexes and comparison with density functional methods

A systematic theoretical investigation on a series of dimeric complexes formed between some halocarbon molecules and electron donors has been carried out by employing both ab initio and density functional methods. Full geometry optimizations are performed at the Moller-Plesset second-order perturbation (MP2) level of theory with the Dunning's correlation-consistent basis set, aug-cc-pVDZ. Binding energies are extrapolated to the complete basis set (CBS) limit by means of two most commonly used extrapolation methods and the aug-cc-pVXZ (X = D, T, Q) basis sets series. The coupled cluster with single, double, and noniterative triple excitations [CCSD(T)] correction term, determined as a difference between CCSD(T) and MP2 binding energies, is estimated with the aug-cc-pVDZ basis set. In general, the inclusion of higher-order electron correlation effects leads to a repulsive correction with respect to those predicted at the MP2 level. The calculations described herein have shown that the CCSD(T) CBS limits yield binding energies with a range of -0.89 to -4.38 kcal/mol for the halogen-bonded complexes under study. The performance of several density functional theory (DFT) methods has been evaluated comparing the results with those obtained from MP2 and CCSD(T). It is shown that PBEKCIS, B97-1, and MPWLYP functionals provide accuracies close to the computationally very expensive ab initio methods.     

用从头算研究Shilov反应的机理

Shilov反应在CH~4活化中占有中心地位,它有氧化加成和σ迁移两种可能的机理。本文用较大基组的从头算研究了这两种机理的反应过程,认为Shilov反应应按氧化加成机理进行。     

三元硼氮环的电子结构与成键

用从头算ＳＣＦ－ ＭＯ法对三元硼氮环２ 个系列８ 个分子的电子结构进行了研究．根据计算结果,由原子的轨道布居以及σ和π电子的分布,讨论了硼原子与氮原子间的成键情况．结果表明,硼原子和氮原子上加Ｈ 有利于环的稳定,同时削弱了Ｂ—Ｎ 键而增强了Ｂ—Ｂ键和Ｎ—Ｎ 键,对Ｂ２Ｎ 系列和ＢＮ２ 系列中的Ｂ原子和Ｎ 原子的净电荷的影响恰好相反．     

Ab initio study of sphere-like mesogen properties

Sphere-like compound C8H17Si(OPhC12H25)3N (1) forms mesophases. In order to investigate the relationship between molecular structure and liquid crystal properties, structural studies are carried out on the model molecules of compound 1 and its substituted derivatives using ah initio calculations. The results show that the cyano or chloro substituted tribenzosilatrane compounds R1Si(OPhR2 )3N (R1 R2 = CN or Cl) have much bigger dipole moments or anisotropy of polarizability and more like sphere than the corresponding alkyl substituted compounds. Cyano or chloro substituted tribenzosilatranes would be better candidates for sphere-like meso-gens.     

Ab initio study of the insertion reactions of Sc+(1D) with HF,HCl, H2O,H2S,NH3, PH3, CH4, and SiH4

The mechanism of scandium cation Sc⁺(¹D) insertion into HF, HCl, H₂O, H₂S, NH₃, PH₃, CH₄, and SiH₄ has been investigated by ab initio molecular theory. All these reactions involve the initial formation of intermediate complexes followed by an H‐atom migration process via a transition state to insertion products. The Sc⁺(¹D) insertion into eight compound reactions indicate that (i) the reaction with hydride of the right‐hand group is more exothermic than that of the left‐hand group and has a lower barrier, and (ii) the reaction with the second‐row hydride has a lower overall barrier and is less exothermic than with the first‐row hydride. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Charge distribution and hydrogen bonding of a collagen α2‐chain in vacuum,hydrated, neutral,and charged structural models

A challenging task in computational biophysics is to ascertain the solvent effect on the electronic structure and interatomic bonding at the atomistic level. Simulations must be carried out on reasonably large biomolecules for accurate calculations to yield valid results. We report the results of a calculation on collagen model in the form of a peptide under three different environments: vacuum, solvated and with neutral and charged sites. Quantitative results and analysis of the partial charge (PC) distribution on each amino acid are discussed. A significant charge transfer of more than 1 electron from protein to water molecules is found with similar results when the model contains charged sites. The main contributions to the interatomic bonding are from hydrogen bonds (HBs) between water‐water and water‐protein pairs. A connection between PC and HBs can be established since the nonpolar amino acids form no HBs and have the smallest PC and vice versa. The ab initio PC obtained are used in the NAMD simulation showing significant improvement over the default values as reflected in the root mean square deviation of atomic positions in the MD steps and the total free energy in energy minimization. These results could facilitate the interpretation of data on interaction of various ligands in charged proteins in relation to isoelectric points. © 2016 Wiley Periodicals, Inc.     

Theoretical study of the intermolecular hydrogen bond interaction for furan-HCl and furan-CHCl_3 complexes

The importance of intermolecular interactions in biology and material science has prompted chemists to explore the nature of the variety of such interactions. The strongest of these interac-tions are the hydrogen bonds, which play an important role in determining the molecular confor-mation, crystal packing, and the structure of biological systems such as nucleic acids. Extensive experimental and theoretical efforts[1—5] have been devoted to the studies of this type of interac-tions, such as …     

Ab initio prediction of the vibrational spectra of the hydrogen‐bonded complexes between CO and HONO2

The vibrational characteristics (vibrational frequencies and infrared intensities) for free and complexed CO and HONO₂ have been predicted using ab initio calculations at SCF and MP2 levels with different basis sets and B3LYP/6?31G(d,p) calculations. The ab initio calculations show that the complexation between HONO₂ and CO leads to two stable structures: CO … HONO₂ (1A) and OC … HONO₂ (1B). The changes in the vibrational characteristics from free monomers to complexes have been estimated. It was established that the most sensitive to the complexation is the stretching O? H vibration. In agreement with the experiment, its vibrational frequency in the complexes is shifted to lower frequency (Δν = ?123 cm^?1). The magnitude of the wave number shift is indicative of relatively strong hydrogen‐bonded interaction. The ab initio calculations at different levels predict an increase of the infrared intensity of the stretching O? H vibration for structure 1A more than five times and for structure 1B more than nine times. The most consistent agreement between the computed values of the frequency shifts for structure 1B and those experimentally observed suggests that this structure is preferred. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003     

Theoretical study of energies,structures, and vibrational spectra of the carbonic acid–hydroperoxy radical complexes

In this work, we present the results for the first time of our study on hydrogen‐bonded H₂CO₃–HO₂ complexes (structures 1, 2) by means of ab initio molecular orbital theory. These complexes are important intermediates in the reaction of the hydroperoxy radical and cabonic acid. We calculated that these structures are a six‐membered ring. We found that the binding energy of two complexes are 5.8 and 9.3 kcal/mol using the CCSD(T) method. We also calculated the vibrational and rotational frequencies for these complexes. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005