基于概念密度泛函理论磷酸酯类反应性物质毒性预测

磷酸酯类反应性物质是乙酰胆碱酯酶不可逆抑制剂。本文应用概念密度泛函理论(CDFT),采用四组条件(B3LYP/6-311++G(2d, 3p)/gas,B3LYP/6-311++G(2d, 3p)/CPCM/water,MP2/6-311++G(2d, 3p)/gas,MP2/6-311++ G(2d, 3p)/CPCM/water),对20多个磷酸酯反应性物质进行反应性描述指数计算,包括分子的化学势μ,绝对硬度η、亲电性指数ω、分子的前线轨道能量等分子整体描述参数,以及原子福井函数、自然键轨道(NBO)电荷、Wiberg键级、NBO键级等分子局域描述参数。通过对反应性描述指数以及定量构性关系(QSPR)方程预测结果的比较分析,得出结论：大多数化合物亲电进攻的反应中心发生在磷原子上;磷酸酯类化合物侧链乙胺基叔氮的质子化,将显著增强反应中心磷原子的亲电进攻能力;B3LYP/6-311++G(2d, 3p)/gas为最合理的计算条件;应用反应性描述指数建立的QSPR模型明显优于常规的2D-QSPR模型,能够用于乙酰胆碱酯酶不可逆抑制剂的精确毒性预测。     

N2O…HOCl复合物结构和性质的理论研究

分别在DFT-B3LYP和MP2/6-311++G**水平上求得HOCl + N2O复合物势能面上的六种(S1, S2, S3, S4, S5和S6)和四种(S1, S2, S4和S5)构型. 频率分析表明,其中的S1和S3为过渡态,其它为稳定构型. 在复合物S3, S5 和S6中,HOCl 单体的σ*(5O-6H)作为质子供体,与N2O单体中作为质子受体的3O原子相互作用,形成氢键结构,而在氢键复合物S2中, 质子受体为N2O单体中的端1N原子;复合物S1中,HOCl分子的σ*(5O-4Cl)作为质子供体与N2O分子中的端1N原子(质子受体)相互作用,形成卤键结构,而复合物S4中的卤键结构的质子受体为N2O分子中的端3O原子. 经B3LYP/6-311++G**水平上的计算,考虑了基组重叠误差(BSSE)校正的单体间相互作用能在-1.56 ~ -8.73 kJ·mol-1之间. 采用自然键轨道理论(NBO)对两种单体间相互作用的本质进行了考查,并通过分子中原子理论(AIM)分析了复合物中氢键和卤键键鞍点处的电子密度拓扑性质.     

Theoretical Study on Vibrational Spectra,Detonation Properties and Pyrolysis Mechanism for Cyclic 2-Diazo-4,6-dinitrophenol

Based on the full optimized molecular geometrical structures at the DFT-B3LYP/6-311+G** level, there exists intramolecular hydrogen bond interaction for cyclic 2-diazo-4,6-dinitrophenol. The assigned infrared spectrum is obtained and used to compute the thermodynamic properties. The results show that there are four main characteristic regions in the calculated IR spectra of the title compound. The detonation velocities and pressures are also evaluated by using Kamlet-Jacobs equations based on the calculated density and condensed phase heat of formation. Thermal stability and the pyrolysis mechanism of 2-diazo-4,6-dinitrophenol are investigated by calculating the bond dissociation energies at the B3LYP/6-311+G** level.     

D-苯丙氨酸与Cu＋(1S0, 3d10)气相反应理论研究

用量子化学密度泛函(DFT)方法研究D-苯丙氨酸与一价基态金属阳离子Cu^＋在气相中反应的机理. 在B3LYP/6-31G*水平上, 优化了反应包含的4个反应通道的反应物、中间体、过渡态和产物的几何构型, 并采用B3LYP/DZVP, B3LYP/[6-311＋G**(C,H,O)＋Lanl2dz(Cu)], B3LYP/6-311＋G**, MP2/6-311＋G** 等方法对各驻点进行了单点能计算. 通过对计算结果的分析, 获得了其单重态反应势能面的一般轮廓、各驻点几何构型优化参数, 明确了其反应机理.     

Ab initio studies of aspartic acid conformers in gas phase and in solution

Systematic and extensive conformational searches of aspartic acid in gas phase and in solution have been performed. For the gaseous aspartic acid, a total of 1296 trial canonical structures and 216 trial zwitterionic structures were generated by allowing for all combinations of internal single-bond rotamers. All the trial structures were optimized at the B3LYP/6-311G* level and then subjected to further optimization at the B3LYP/6-311++G** level. A total of 139 canonical conformers were found, but no stable zwitterionic structure was found. The rotational constants, dipole moments, zero-point vibrational energies, harmonic frequencies, and vertical ionization energies of the canonical conformers were determined. Single-point energies were also calculated at the MP2/6-311++G** and CCSD/6-311++G** levels. The equilibrium distributions of the gaseous conformers at various temperatures were calculated. The proton affinity and gas phase basicity were calculated and the results are in excellent agreement with the experiments. The conformations in the solution were studied with different solvation models. The 216 trial zwitterionic structures were first optimized at the B3LYP/6-311G* level using the Onsager self-consistent reaction field model (SCRF) and then optimized at the B3LYP/6-311++G** level using the conductorlike polarized continuum model (CPCM) SCRF theory. A total of 22 zwitterions conformers were found. The gaseous canonical conformers were combined with the CPCM model and optimized at the B3LYP/6-311++G** level. The solvated zwitterionic and canonical structures were further examined by the discrete/SCRF model with one and two water molecules. The incremental solvation of the canonical and zwitterionic structures with up to six water molecules in gas phase was systematically examined. The studies show that combining aspartic acid with at least six water molecules in the gas phase or two water molecules and a SCRF solution model is required to provide qualitatively correct results in the solution.     

Intramolecular hydrogen bond in 3‐imino‐propenylamine isomers: AIM and NBO studies

The molecular structure and intramolecular hydrogen bond energy of 18 conformers of 3‐imino‐propenyl‐amine were investigated at MP2 and B3LYP levels of theory using the standard 6‐311++G** basis set. The atom in molecules or AIM theory of Bader, which is based on the topological properties of the electron density (ρ), was used additionally and the natural bond orbital (NBO) analysis was also carried out. Furthermore calculations for all possible conformations of 3‐imino‐propenyl‐amin in water solution were also carried out at B3LYP/6‐311++G** and MP2/6‐311++G** levels of theory. The calculated geometrical parameters and conformational analyses in gas phase and water solution show that the imine–amine conformers of this compound are more stable than the other conformers. B3LYP method predicts the IMA‐1 as global minimum. This stability is mainly due to the formation of a strong N? H···N intramolecular hydrogen bond, which is assisted by π‐electrons resonance, and this π‐electrons are established by NH2 functional group. Hydrogen bond energies for all conformers of 3‐imino‐propenyl‐amine were obtained from the related rotamers methods. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Investigation of the use of B3LYP zero-point energies and geometries in the calculation of enthalpies of formation

The use of B3LYP/6–31G^* zero-point energies and geometries in the calculation of enthalpies of formation has been investigated for the enlarged G2 test set of 148 molecules [J. Chem. Phys. 106 (1997) 1063]. A scale factor of 0.96 for the B3LYP zero-point energies gives an average absolute deviation nearly the same as scaled HF/6–31G^* zero-point energies for G2, G2(MP2), and B3LYP/6–311 + G(3df,2p) enthalpies. A scale factor of 0.98, which has been recommended in some studies, increases the average absolute deviation by about 0.2 kcal/mol. Geometries from B3LYP/6–31G^* are found to do as well as MP2/6–31G^* geometries in the calculation of the enthalpies of formation.     

Study of conformational and optical rotation for the alaninamide

Six stationary points of alaninamide have been located on the potential surface energy (PES) at the B3LYP/6‐311++G(2d,2p) level of theory both in the gas phase and in aqueous solution. In the aqueous solution, to take the water solvent effect into account, the polarizable continuum model (PCM) method has been used. Accurate geometric structures and their relative stabilities have been investigated. The results show that the intramolecular hydrogen bond plays a very important role in stabilizing the global minimum of the alaninamide. Moreover, the consistent result in relative energy using high‐level computations, including the MP2 and MP3 methods with the same basis set [6‐311++G(2d,2p)], indicates that the B3LYP/6‐311++G(d,p) level may be applied to the analogue system. More importantly, the optical rotation of the optimized conformers (both in the gas phase and in aqueous solution) of alaninamide have been calculated using the density functional theory (DFT) and Hartree–Fock (HF) method at various basis sets (6‐31+G*, 6‐311++G(d,p), 6‐311++G(2d,2p) and aug‐cc‐pvdz). The results show that the selection of the computation method and the basis set in calculation has great influence on the results of the optical rotations. The reliability of the HF method is less than that of DFT, and selecting the basis set of 6‐311++G(2d,2p) and aug‐cc‐pvDZ produces relative reliable results. Analysis of the computational results of the structure parameters and the optical rotations yields the conclusion that just the helixes in molecules caused the chiral molecules to be optical active. The Boltzmann equilibrium distributions for the six conformers (both in the gas phase and in the aqueous solution) are also carried out. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

2,3,7,8-四氯苯并二英分子结构与热力学性质的理论研究

用密度泛函理论(DFT)和从头算(ab initio)方法,在B3LYP/6-31G、 B3LYP/6-31G*、 B3LYP/6-311G*和MP2/6-31G*水平上全优化计算了2,3,7,8-四氯苯并二英(2,3,7,8-TCDD)的几何构型、电子结构和振动频率,并用校正后的频率计算了298～1500 K的标准热力学函数,同时用半经验的PM3 SCF-MO进行了同样的计算,计算结果与实验值及文献值较好地吻合.     

Theoretical studies on the reaction of pentafulvenone with water in gas phase and aqueous solvent

In gas phase, the hydrations of pentafulvenone to generate three types of cyclopentadienyl carboxylic acids are studied theoretically at the MP2/6-311+G**//B3LYP/6-311+G** level. A water molecule attacking the C=O double bond of pentafulvenone can yield cyclopentadienyl carboxylic acids via the formation of fulvenediols, and attacking the C=C double bond of pentafulvenone can directly yield cyclopentadienyl carboxylic acid. The barriers of rate-determining transition states are 42.2 and 30.4 kcal mol⁻¹, respectively. The barriers of rate-determining transition states for two water molecules system are 20.2 and 19.6 kcal mol⁻¹, respectively. The products can isomerize to each other. In aqueous solvent, the hydrations of pentafulvenone are investigated using PCM-UAHF model at the MP2 (PCM)/6-311+G**// B3LYP (PCM)/6-311+G** and MP2 (PCM)/6-311+G**// B3LYP/6-311+G** levels. The barriers of all rate-determining transition states are decreased. The added water molecule acts as catalyst in both gas phase and aqueous solvent. Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Thermochemistry of the higher chlorine oxides ClOx (x=3, 4) and Cl2Ox (x=3–7)†

Heats of formation for ClO₃, ClO₄, Cl₂O₃, Cl₂O₄, Cl₂O₅, Cl₂O₆ and Cl₂O₇ molecules are determined at the B3LYP, B3PW91, mPW1PW91 and B1LYP levels of the density functional theory employing a series of extended basis sets, and using Gaussian-3 model chemistries. Modified Gaussian-3 calculations, which employ accurate B3LYP/6-311+G(3d2f) molecular geometries and vibrational frequencies, were also performed. Heats of formation were calculated from both total atomization energies and isodesmic reaction schemes. The latter method in conjunction with Gaussian-3 models leads to the most reliable results. The best values at 298 K for ClO₃, ClO₄, Cl₂O₃ and Cl₂O₄ as derived from an average of G3//B3LYP and G3//B3LYP/6-311+G(3d2f) calculations are 43.1, 54.8, 31.7 and 37.4 kcal mol⁻¹. From calculations carried out at the G3(MP2)//B3LYP and G3(MP2)//B3LYP/6-311+G(3d2f) levels, heats of formation for Cl₂O₅, Cl₂O₆ and Cl₂O₇ are predicted to be 53.2, 52.2 and 61.5 kcal mol⁻¹. All best values are reproduced within 1 kcal mol⁻¹ by using mPW1PW91/6-311+G(3d2f) isodesmic energies. Enthalpy changes for relevant Cl–O bond fission reactions are reported. Comparisons with previous thermodynamics data are made.     

Inductive effects in radicals calculated from DFT energies; substituted bicyclo[2.2.2]octan-1-yloxy radicals

Energies of a series of 4-substituted 1-oxybicyclo[2.2.2]octan-1-yloxy radicals with 18 various substituents were calculated within the framework of the DFT theory at the levels UB3LYP/6-311+G(d,p)//UB3LYP/6-311+G(d,p) and UB3LYP/6-311++G(2df,p)//UB3LYP/6-311+G(d,p) and compared with similar series of the parent alcohols, their deprotonated and protonated forms calculated at the levels B3LYP/6-311+G(d,p)//B3LYP/6-311+G(d,p) and B3LYP/6-311++G(2df,p)//B3LYP/6-311+G(d,p). The two levels are of the same performance and both are sufficient for molecules of this type according to comparison with scarce experimental gas-phase acidities and basicities. The substituent effects were analyzed in terms of isodesmic equations. In addition to strong dependence on the substituent inductive effect, a slight dependence on the electronegativity of the first atom of the substituent was proven in certain cases. In all aspects, there is no qualitative difference between the effects on radicals and on similar closed shell species. Radicals behave as slightly electron deficient; the substituent effect is weaker than that on the ions but stronger than on neutral molecules.     

DFT and experimental studies of the structure and vibrational spectra of curcumin

The potential energy surface of curcumin [1,7‐bis(4‐hydroxy‐3‐methoxyphenyl)‐1,6‐heptadiene‐3,5‐dione] was explored with the DFT correlation functional B3LYP method using 6‐311G* basis. The single‐point calculations were performed at levels up to B3LYP/6‐311++G**//B3LYP/6‐311G*. All isomers were located and relative energies determined. According to the calculation the planar enol form is more stable than the nonplanar diketo form. The results of the optimized molecular structure are presented and compared with the experimental X‐ray diffraction. In addition, harmonic vibrational frequencies of the molecule were evaluated theoretically using B3LYP density functional methods. The computed vibrational frequencies were used to determine the types of molecular motions associated with each of the experimental bands observed. Our vibrational data show that in both the solid state and in all studied solutions curcumin exists in the enol form. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

An ab initio study of water clusters in gas phase and bulk aqueous media: (H2O)n,n=1–12

Geometries of several clusters of water molecules including single minimum energy structures of n‐mers (n=1–5), several hexamers and two structures of each of heptamer to decamer derived from hexamer cage and hexamer prism were optimized. One structural form of each of 11‐mer and 12‐mer were also studied. The geometry optimization calculations were performed at the RHF/6‐311G* level for all the cases and at the MP2/6‐311++G** level for some selected cases. The optimized cluster geometries were used to calculate total energies of the clusters in gas phase employing the B3LYP density functional method and the 6‐311G* basis set. Frequency analysis was carried out in all the cases to ensure that the optimized geometries corresponded to total energy minima. Zero‐point and thermal free energy corrections were applied for comparison of energies of certain hexamers. The optimized cluster geometries were used to solvate the clusters in bulk water using the polarized continuum model (PCM) of the self‐consistent reaction field (SCRF) theory, the 6‐311G* basis set, and the B3LYP density functional method. For the cases for which MP2/6‐311++G** geometry optimization was performed, solvation calculations in water were also carried out using the B3LYP density functional method, the 6‐311++G** basis set, and the PCM model of SCRF theory, besides the corresponding gas‐phase calculations. It is found that the cage form of water hexamer cluster is most stable in gas phase among the different hexamers, which is in agreement with the earlier theoretical and experimental results. Further, use of a newly defined relative population index (RPI) in terms of successive total energy differences per water molecule for different cluster sizes suggests that stabilities of trimers, hexamers, and nonamers in gas phase and those of hexamers and nonamers in bulk water would be favored while those of pentamer and decamer in both the phases would be relatively disfavored. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 81: 90–104, 2001     

Post Hartree–Fock and density functional theory studies on Di-Protonated Allopurinol

Post Hartree–Fock and density functional theory (DFT) methods have been employed to study the molecular properties of Di-Protonated Allopurinol²⁺ tautomers in gaseous and aqueous phase environments. The tautomers in gaseous phase have been optimized at MP2/6-311G(2d,2p) and B3LYP/6-311G(2d,2p) levels of theory. The self-consistent reaction field theory (SCRF) has been employed to optimize the tautomers in aqueous phase (ε = 78.5) at B3LYP/6-311G(2d,2p) level of theory and the solvent effect has been studied. The structure, energetics and relative stabilities of the tautomers have been analyzed both in gaseous and aqueous phases. The principle of maximum hardness (MHP) has been tested at B3LYP/6-311G(2d,2p) level of theory. The condensed Fukui functions have been calculated using the atomic charges obtained through Natural population analysis to identify the relative change in the most reactive site of the optimized structures. NMR studies have been carried out, on the basis of Cheeseman coworker’s method, to analyze the molecular environment as well as the delocalization activities of electron clouds.