Hydrogen Bonding Character Between the Glycine and BF4-

在B3LYP/6-31+G^*水平上研究BF₄^-与甘氨酸间氢键作用特征,并在B3LYP/6-311++G^**水平上计算单点能. 对二聚物几何结构、能量、氢键成键特征进行分析. 分子中的原子拓扑分析表明氢键成键原子间存在(3,-1)关键点,电子密度和Laplacian量落在氢键范围内. 进一步对氢键形成导致H原子净电荷、偶极矩、能量及体积的改变进行系统分析.     

水合亮氨酸构型的系统寻找与研究

同时考虑亮氨酸可能的水分子络合方式及亮氨酸分子的所有内轴转动,对亮氨酸与1～3个水分子的复合结构Leu-(H₂O)_n进行了系统寻找．分别用BHandHLYP/6-31+G*和BHandHLYP/6-311++G**方法对结构进行了优化和单点能计算．发现亮氨酸水合结构与孤立亮氨酸有着很好的对应关系,且亮氨酸的水合结构可以可靠地通过对亮氨酸的结构直接加水得到．对中性、双电性亮氨酸水合结构的红外计算光谱与溶液中亮氨酸实验光谱进行了比较与分析,发现双电性Leu-(H₂O)₃的红外光谱与实验符合得最好,表明溶质在气相中与适量的水分子络合便能较好地模拟溶质在溶液中的红外光谱．     

CH3⊕ … Br-Y(Y=H, CCH, CN, NC)缺电子体系中Br原子参与的反向卤键相互作用

采用B3LYP/6-311++G(d,p)和MP2/6-311++G(d,p)理论方法研究了CH₃^⊕…Br-Y(Y=H, CCH, CN, NC) 缺电子体系中Br参与的反向卤键(IXB)结构. 四个IXB复合物中,MP2/6-311++G(d,p)水平上考虑了基组叠加误差的分子间相互作用能分别为218.87, 219.48, 159.18和143.05 kJ/mol,相对稳定性的递增顺序CH₃^⊕…BrCN相似文献   

五种典型力场对气相中不同末端氨基酸的表现

选择了Amb-er99SB、CHARMM27、ENCADS、GROMOS-53A6和OPLSAA/L五种力场,并以BHandHLYP/6-311++G**优化后的气象氨基酸构型与能量作为参考标准. 研究了中性、质子化、去质子化和带帽氨基酸在不同力场下的表现. 比较了构型相对能量、顺反式结构能量差、氢键数目与强度和优化所得构型质量等代表性结果. AMBER99SB、CHARMM27和OPLSAA/L比较GROMOS53A6和ENCADS力场更为适用于气相氨基酸. 对一般性气象氨基酸和小肽分子,最推荐的力场是CHARMM27,其次为OPLSAA/L.     

利用红外多光子解离光谱和理论计算揭示由脯氨酸和苯丙氨酸构成的质子化异源二聚体的结构

本文利用傅里叶变换离子回旋质谱仪和红外光学参量振荡器激光器相结合,在2700∽3700 cm^-1范围内获得了由脯氨酸和苯丙氨酸组成的质子化异源二聚体ProPheH⁺的红外多质子解离(IRMPD)光谱. 实验光谱表明,ProPheH⁺除了在3565 cm^-1处有一个对应于自由羧基O$-$H拉伸振动的吸收峰之外,在2935 cm^-1和3195 cm^-1处有两个宽吸收峰. 进一步对ProPheH⁺的结构在M062X/6-311++G(d,p)水平上进行了广泛的理论计算. 结果表明,其能量最稳定的构型具有电荷溶剂化结构,其中质子与脯氨酸单元结合. 这一构型的理论预测光谱与实验谱吻合较好.     

3-二甲氨基-2-甲基丙烯醛S2激发态结构动力学 (cited: 3)

采用共振拉曼光谱和完全活性自洽场理论计算研究了3-二甲氨基-2-甲基丙烯醛(DMAMP)光激发到S₂(ππ^*)态后的光物理性能．在B3LYP/6-311++G(d,p)水平计算确定了DMAMP与其三种异构体之间的基态异构化能垒,指认了振动光谱．采用涵盖紫外强吸收带的激光波长,获得了DMAMP在环己烷、乙腈和甲醇溶剂中的A-带共振拉曼光谱,含时密度泛函方法计算确定了该光谱中基频的相对强度,发现振动-电子耦合发生在S₂(ππ^*)态的Franck-Condon区域．CASSCF计算方法确定低单重和三重激发态、势能面锥形交叉点和系间窜跃点的激发能．共振拉曼光谱强度模式分析和CASSCF计算获得了DMAMP的A-带短时结构动力学和其后的衰变动力学表明,C1=O6和C2=C3之间的瞬时去共轭效应发生在S₂(ππ^*)态的Franck-Condon区域,激发态电荷重分布机制表明,C3和二甲氨基之间以及C1和C2之间的共轭增强效应发生在波包离开Franck-Condon区域后．C1=O6和C2=C3之间的去共轭效应使得-C3=N(CH₃)₂沿着C2-C3键旋转更加容易,C1-C2之间以及C3和N(CH₃)的共轭增强效应使得绕C1-C2和C3-N5旋转变得比较困难．这些表明DMAMP初始结构动力学沿着CI-1(S₂/S₀)交叉点展开,而沿CI-2(S₂/S₀)和CI-3(S₂/S₀)交叉点展开的几率可以忽略．提出了DMAMP分子受光激发从S_2,FC(ππ^*)经由各锥形交叉点和各系间窜跃点回到S₀或T_1,min的两个衰变通道.     

乙腈-水和乙二醇-水均相溶液中光诱导杜醌激发三重态与色氨酸、酪氨酸的氢原子转移反应

本文用激光闪光光解技术研究了光诱导生物醌杜醌激发三重态(³DQ^*)和色氨酸(Trp)与酪氨酸(Tyr)在乙腈-水(MeCN-H₂O)及乙二醇-水(EG-H₂O)均相溶液中的光化学反应,分析了反应的机理,并基于Stern-Volmer方法测量了反应速率常数. 光解DQ体系可以生成³DQ^*,³DQ^*与Trp、Tyr发生的氢原子转移反应占主导地位. 对于DQ/Trp/MeCN-H₂O和DQ/Trp/EG-H₂O溶液,³DQ^*与Trp反应生成杜醌中性自由基DQH^·、以碳为中心的色氨酸中性自由基Trp^·/NH和以氮为中心的色氨酸中性自由基Trp/N^·. 对于DQ/Tyr/MeCN-H₂O和DQ/Tyr/EG-H₂O溶液,³DQ^*与Tyr反应生成DQH^·和酪氨酸中性自由基Tyr/O^·. ³DQ^*与Trp、Tyr的氢原子转移反应速率常数都在10⁹ L·mol^-1·s^-1量级,反应近似受扩散控制. MeCN/H₂O均相溶液中³DQ^*与Trp、Tyr的反应速率常数要明显高于EG/H₂O均相溶液中的反应速率常数,这与Stokes-Einstein方程定性一致.     

SiO2分子的基态(X1A1)结构与分析势能函数

应用群论及原子分子反应静力学方法推导了SiO₂分子的电子态及其离解极限，采用B3P86方法，在6-311G^**水平上,优化出SiO₂基态分子稳定构型为单重态的C_2V构型，其平衡核间距R_e=R_Si—O=0.1587 nm,∠OSiO＝111.2°,能量为-440.4392 a.u..同时计算出基态的简正振动频率:对称伸缩振动频率ν(B₂)=945.4cm^-1，弯曲振动频率ν(A₁)=273.5 cm^-1和反对称伸缩振动频率ν(A₁)=1362.9cm^-1.在此基础上，使用多体项展式理论方法，导出了基态SiO₂分子的全空间解析势能函数，该势能函数准确再现了SiO₂(C_2V)平衡结构.     

空间羣算符的矩阵元

本文首先通过对波失星直接乘积的分析指出,如果 ^*K″∈^*K?^*K′,则波矢峯G_k″可以有下面四种情况:A)G_k同G_k′,是G_k″的子峯,B)G_k=G_k′=G_k″,C)G_k″=G_s, D)G_s是G_k″的子峯。根据上述四种情况,分别考虑积分A=μ″^i″(k″)|f_μⁱ(k)|f_μ′^i′(k′)>的简约。并且证明,对所有四种情况,积分A的值均可由短阵U的矩阵元统一地表达出来。矩阵U是使可约表示Г′简约的转换矩阵,对四种情况,可约表示Г′分别是:A)(Г_kⁱ?Г_k′^i′)^(?),B)Гⁱ?Г_k′^i′,C)Г_k^i(s)?Г_k′^i′(s),D)(Г_k^i(s)?Г_k′^i′(s))^(?)。最后,利用准投影算符的方法,对矩阵U进行了计算,导出空间峯Wigner-Eckart定理的表式。     

聚酰胺胺分子和纳米二氧化硅复合过程的从头计算

通过密度泛函理论在气相条件下, 利用UB3LYP/6-311G(d)和HF/6-31G基组水平优化了过渡态的结构并寻找了能量最低点,发现酰胺氮和亚胺氧是最佳结合点,并分析了这些活性点的活化能大小以及≡Si⁺和≡SiO^-基团和这些活性点的反应步骤,得出静电作用和离子配位效应是形成稳定复合物的主要因素,另外在形成稳定复合物过程中,亚胺氧转向作用和支链的大小和转向对降低整个复合物能量也起着重要的作用．     

An ab initio study of the electronic and geometric structures of SimCn + cationic nanoclusters

The theoretical formalism of local density approximation (LDA) to density functional theory (DFT) has been used to study the electronic and geometric structures of Si_mC_n⁺ (1≤m, n ≤4) cationic clusters. An all electron 6-311++G^** basis set has been used and complete geometry optimizations of different possible structures for a specific cluster have been carried out. Binding energies, relative energies, fragmentation energies, vibrational frequencies, and adiabatic ionization potentials of the optimized clusters have been investigated and reported in detail. Results have been compared with other experimental and theoretical results available in the literature.     

Gas-phase quasi-degeneracy of zwitterionic and canonical tautomers of glycine and proline induced by the presence of the MAlF4 (M = Li,Na, K) salts

The ionic MAlF₄ salts (M = Li, Na, K) are postulated to act as effective stabilising agents with respect to glycine and proline zwitterionic tautomers. On the basis of ab-initio MP2/6-311++G(d,p) theoretical calculations, it is demonstrated that strong electrostatic interactions between the polar MAlF₄ moiety and either Gly and Pro zwitterion should allow to suppress the intra-molecular proton transfer in the amino acid and thus render the zwitterion tautomer stable in the gas phase. Among the systems proposed, the K⁺AlF₄^– turned out to be the most efficient stabilising compound as its presence is expected to lead to the energetic quasi-degeneracy of the canonical and zwitterionic tautomers of glycine and proline.     

Influence of rotational barrier of single-molecule electric revolving door on energies,aromaticity and quadrupole moment

We studied the response of rotation of spindle ring on energies, aromaticity and quadrupole moment in single-molecule revolving door (S-MERD) by using M05-2X/6-311++G^** level of theory. The rotational barrier was considered about the spindle ring from 0° to 180° by 10° intervals. Energies, aromaticity and quadrupole moment values are dependent on the rotation of spindle ring of S-MERD and were plotted as functions of rotation of spindle ring. Rotational barrier of energies, aromaticity and quadrupole moment for all substituents produces a cos²θ function. The nucleus-independent chemical shifts (NICS) of spindle ring increase as the spindle ring gradually rotates out of planarity and reach the highest NICS in the perpendicular conformation. For all substituents, the values of quadrupole moment of spindle ring decrease from 0° to 90° and then increase from 90° to 180°.     

甲基乙烯醚和OH反应机理的理论研究

利用量子化学从头计算的方法对甲基乙烯醚的两个异构体之间的转化,羟基与顺式-甲基乙烯醚和反式-甲基乙烯醚的加成反应,以及羟基提取甲基上的氢原子的反应机理进行了研究.研究结果表明:顺式-甲基乙烯醚比反式-甲基乙烯醚更加稳定,在QCISD/6-31G(d,P)//BHandHLYP/6.311 G(d,P)理论水平下,OH加到顺式-甲基乙烯醚1号住的碳原子上需要跨越的能垒比其它反应通道需要跨越的能垒少7.5～34 KJ/mol,因此是主要的反应通道,而OH加在反式.甲基乙烯醚2号位的碳原子上所需要跨越的能垒比其它反应路径所需要跨越的能垒少8.3～26.7 kJ/mol,因此是主要的反应路径.利用经典过渡态理论计算了总的速率常数     

Rotational spectra, nuclear quadrupole hyperfine tensors, and conformational structures of the mustard gas simulent 2-chloroethyl ethyl sulfide

Rotational spectra have been recorded for both the ³⁵Cl and ³⁷Cl isotopic forms of two structural conformations of 2-chloroethyl ethyl sulfide (CEES). The rotational constants of the ³⁵Cl and ³⁷Cl isotopomers were used to identify the conformational isomers. A total of 236 hyperfine transitions have been assigned for 47 rotational transitions of the ³⁵Cl isotope of a GGT conformer, and 146 hyperfine have been assigned for 37 rotational transitions of the ³⁷Cl isotopomer. For the second conformer, a total of 128 (110) hyperfine and 30 (28) rotational transitions have also been assigned to the ³⁵Cl (³⁷Cl) isotopes of a TGT conformation. The extensive hyperfine splitting data, measured to high resolution with a compact Fourier transform microwave spectrometer, were used to determine both the diagonal and off-diagonal elements of the ³⁵Cl and ³⁷Cl nuclear quadrupole coupling tensors in the inertial tensor principal axis system. The experimental rotational constant data, as well as the ³⁵Cl and ³⁷Cl nuclear quadrupole coupling tensors, were compared to the results from 27 optimized ab initio (HF/6-311++G^∗∗ and MP2/6-311++G^∗∗) model structures.     

外电场下二氧化锆的分子结构及其特性

对O原子采用6-311++G*基组,Zr原子采用aug-cc-pVTZ-PP基组,利用密度泛函(B3P86)方法优化得到了ZrO2分子的稳定构型,并研究了不同外电场(0—0.025 a.u.)作用下ZrO2基态分子键长、能量、电荷分布、偶极矩和能级的变化规律.在优化构型的基础上,利用含时密度泛函(TD-B3P86)方法研究了ZrO2分子在外电场作用下前6个激发态的激发能、跃迁波长和振子强度的激发特性.研究结果表明:随着电场强度的增大,Zr—2O的键长增大,而Zr—3O的键长均匀减少,总能量降低,偶极矩增大;最高占据轨道能量基本保持不变,最低未占据轨道和能隙均减小.电场的增大使得激发能减小,各个激发态跃迁波长均发生不同程度的红移现象,因而,利用外电场可以控制ZrO2的发光光谱范围在可见-红外区域扩展.     

Mass spectrometric and ab initio study of the interaction between 9-methylguanine and amino acid amide group

The temperature dependent field ionization mass spectrometry method combined with ab initio calculations was used to determine the interaction energies and the structures of 9-methylguanine-acrylamide dimers. Acrylamide mimics the side chain amide group of the natural amino acids asparagine and glutamine. The experimental enthalpy of the dimer formation derived from the van't Hoff plot is ?59.5 ± 3.8 kJ mol^?1. The value is higher than interaction energies between acrylamide and other nucleic acid bases which were determined to be ?57.0 for 1-methylcytosine, ?52.0 for 9-methyladenine, and ?40.6 kJ mol^?1 for 1-methyl-uracil. In total, eight hydrogen bonded dimers formed by the three lowest energy 9-methylguanine tautomers and acrylamide were found in the quantum chemical calculations performed at the DFT/B3LYP/6-31++G?? and MP2/6-31++G?? levels of theory. The relative stability and the interaction energies of the dimers were calculated accounting for the basis set superposition error and the zero-point vibrational energy correction. The lowest energy dimer found in the calculations is formed by acrylamide (Ac) with the keto tautomer of 9-methylguanine (Gk). It is stabilized by two intermolecular H bonds, C6=O(Gk) · · · H—N(Ac) and Nl—H(Gk) · · ·O(Ac), and it is more stable than the second lowest energy dimer by ≈ 25 kJ mol^?1. The calculated interaction energies of the lowest energy 9-methylguanine-acrylamide dimer are ?65.0 kJ mol^?1 and ?67.7 kJ mol^?1 at the MP2 and DFT levels of theory, respectively. The experimental enthalpy of the dimer formation is in good agreement with both the calculated interaction energies of the GkAc dimer and much higher than the interaction energies calculated for all other 9-methylguanine-acrylamide dimers. This proved that only one dimer was present in the experimental samples. To verify whether acrylamide is a good model of the amino acid-amide group, we performed direct calculations of the 9-methylguanine-glutamine dimers at the same levels of theory as used for the complexes involving acrylamide. The interaction energies found for the lowest energy 9-methylguanine-glutamine dimer are ?65.1 kJ mon^?1 (MP2/6-31++G??) and ?66.2 kJ mol^?1 (DFT/B3LYP/6-31++G??) and these values are very close (within 0.5 kJ mol^?1) to the interaction energies obtained for the 9-methylguanine-acrylamide dimers.