2-亚胺-1,10-邻二氮杂菲铁(Ⅱ)类催化剂活性与中心金属原子净电荷的关系

应用金属原子净电荷相关性(MANCC)方法研究了铁(Ⅱ)类催化剂活性. 取代基的电子效应占主导作用的催化剂, 活性与中心金属原子净电荷有较好的相关性. 当取代基呈供电子效应时, 催化剂活性随着电荷的增大而升高, 当取代基呈吸电子效应时, 催化剂活性随着电荷的增大而降低. 在此基础上推测烯烃聚合反应催化过程中可能存在两种不同的活性中心, 一种是[LFe-R]⁺, 另一种是[LFe-R]²⁺或[Fe(Cl)RL]⁺. 当取代基的电子效应和空间效应均对活性有影响时, 发现催化剂的两卤素净电荷差值越小, 催化活性越强.     

取代苯甲酸羧基上H和O原子的部分电荷与Hammett常数之间的线性关系

采用密度泛函分析了取代苯甲酸中羧基上的H1原子和2个氧原子O2和O3的电荷与取代基的Hammett常数之间的线性关系. 比较了不同密度泛函和电荷计算方法B3LYP/6-311G*/(NBO, Mulliken), (BLYP, BP, PWC)/DNP/(Hirshfeld, Mulliken)对上述线性相关系数的影响. 结果表明, BLYP/DNP/Hirshfeld方法的计算精度高且计算速度快. 使用BLYP/DNP/Hirshfeld方法计算了70个取代苯甲酸的部分电荷, 发现H1, O2和O3原子的电荷与取代基Hammett常数σ_p和σ_m之间的线性相关系数可达到0.98以上, 其中O2的电荷和Hammett常数的线性相关性最好. O2的电荷值可以作为Hammett常数的替代, 用于结构性能定量分析, 也可以用于预测取代基的Hammett常数.     

Pd_xNi/C催化剂增强机理的密度泛函理论研究

通过交替微波法制备了PdxNi/C(x=1～4)催化剂,并对其形貌、结构及电化学性能进行了表征.结果表明,通过在Pd中掺杂Ni原子,其对氧还原反应(ORR)的催化活性较纯Pd的高.同时采用密度泛函理论(DFT)计算了一系列简化的团簇模型.计算结果表明,随着Ni的加入,纳米颗粒的最高占据轨道(HOMO)与最低空轨道(LUMO)能级增加,且两能级间隙(HLG)减小.因此在ORR中,一方面由于LUMO被抬高,降低了电子亲和能,带负电的催化剂颗粒更易将电子传递给O2,另一方面由于HLG减小,电中性颗粒HOMO上的电子也容易失去.这两方面的作用使其对O2还原活性得以增强.Fukui指数结合DFT方法和Mulliken布居分析指出,表面的Pd原子为催化剂团簇的活性中心.     

Diels-Alder反应活性的量子化学计算研究

通过HF/6-31G*方法对Diels-Alder反应的一些双烯体及亲双烯体分子进行了结构优化和能量计算。对分子的LUMO、HOMO轨道能量的分析发现,给电子取代基双烯体与吸电子取代基亲双烯体、吸电子取代基双烯体与给电子取代基亲双烯体的Diels-Alder反应较易进行,只是反应开始第一步两者电子流向相反。计算结果表明,反应进行的可能性与一个反应分子LUMO轨道和另一个反应分子HOMO轨道能量之差呈正相关。     

抗癌性吲哚喹唑啉衍生物的定量构效关系

用量子化学密度泛函理论(DFT)、分子力学(MM＋)及回归分析方法,对一系列抗癌性吲哚喹唑啉衍生物进行了定量构效关系(QSAR)的研究.通过回归分析,筛选了影响抗癌活性的主要因素,建立了定量构效关系方程.结果表明,化合物的最低未占据分子轨道(LUMO)与最高占据分子轨道(HOMO)之间的能量差(ΔεL-H)、分子的疏水性(lgP)以及环D上的总电荷(ΣQD)和环D上R1取代基的第一个原子的净电荷(QFR1)是影响化合物抗癌活性的主要因素.所得模型对化合物抗癌活性有较好的预测效果. 同时, 与ΔεL-H密切相关的LUMO轨道能量及共轭平面面积对药物的DNA-结合及其活性起着十分重要的作用,可通过选取具有较强的拉电子性质同时又能与本系列化合物的骨架形成更大共轭体系的取代基R1,设计抗癌活性较高的化合物.     

芳香化合物亲核、亲电反应活性的理论预测和实验反应速率的相关性研究

选择自然布局分析(NPA)电荷、Hirshfeld电荷、分子范德华表面1.6?处的静电势、最低未占据轨道(LUMO)成分、分子范德华表面1.6?处的平均局部离子化能、简缩福井函数和简缩双描述符来预测芳香族化合物亲核加成、亲核取代和亲电反应的活性位点,并分析理论预测结果和实验反应速率之间的相关性.发现这些方法都能准确地预测反应的活性位点.还发现不管对亲核反应还是对亲电反应,体现局部电子硬度的方法,如Hirshfeld电荷和分子范德华表面1.6?处的静电势,其预测结果的大小能较好地反映实验反应速率的相对大小,而体现局部电子软度的方法,简缩福井函数和简缩双描述符,其预测结果和实验反应速率的相关性较小.     

偶氮染料分子的电子结构与生物降解活性(Ⅱ)-取代基非定域活性对偶氮键还原裂解的影响

通过ＭＮＤＯ计算及相关实验结果,用取代基非定域活性概念分析了羟基、氨基及硝基在—ＮＮ—上的电子效应,阐述了取代基影响偶氮键生物降解活性的电子结构机理,并提出将ＭＮＤＯ统计集居分析中的活性电荷ＱＡ（其值可反映原子在分子中的化学活性）作为关联偶氮键生物降解活性的电子结构参数     

电子效应对单取代苯定位效应和反应活性的影响

单取代苯的定位效应和反应活性主要受取代基的电子效应控制,列表总结了取代基的电子效应与定位效应和反应活性的关系,分析了烃基电子效应的特殊性,取代基具有-Ⅰ效应的普遍性。除卤素取代基外,探讨了共轭效应的方向对定位效应和反应活性的决定作用。     

原子电荷计算方法的对比

原子电荷是对化学体系中电荷分布最简单、最直观的描述形式之一,在理论和实际应用中都有重要意义.本文介绍了12种重要的原子电荷计算方法的原理和特点,通过大量实例从不同角度比较了它们的优缺点.这些方法包括Mulliken、分子环境中的原子轨道(AOIM)、Hirshfeld、原子偶极矩校正的Hirshfeld布居(ADCH)、自然布居分析(NPA)、Merz-Kollmann(MK)、分子中的原子(AIM)、Merck分子力场94(MMFF94)、AM1-BCC、Gasteiger、电荷模型2(CM2)以及电荷均衡(QEq)方法.最后本文对如何在实际应用中选择合适的计算方法给出了建议.     

吲哚并咔唑类衍生物载流子传输性质的理论研究

以密度泛函理论结合跳跃模型, 重点研究了氯原子和烷基链的引入对吲哚并咔唑类衍生物传输性质的影响. 计算结果表明, 与吲哚并[3,2-b]咔唑(1)相比, 氯原子的引入增大了2,8-二氯吲哚并[3,2-b]咔唑(2)和2,8-二氯-5,11-二己基吲哚并[3,2-b]咔唑(3)的最高占据分子轨道(HOMO)的离域程度, 而对最低未被占据分子轨道(LUMO)则无显著贡献, 但明显降低了二者的能级. 上述结果表明, 对于LUMO, 氯原子体现了吸电子效应, 而对于HOMO, 氯原子体现了共轭效应. 烷基链的引入使化合物3的空穴迁移率明显高于化合物1和2, 这主要归因于化合物3具有更加紧密的分子堆积, 尤其在跳跃路径A中, 具有更大的分子间电子耦合和轨道重叠. 同时能带结构的计算结果进一步证明, 氯原子和烷基链的同时引入大大改善了吲哚并咔唑类衍生物的电荷传输性能.     

Atomic charges,dipole moments,and Fukui functions using the Hirshfeld partitioning of the electron density

In the Hirshfeld partitioning of the electron density, the molecular electron density is decomposed in atomic contributions, proportional to the weight of the isolated atom density in the promolecule density, constructed by superimposing the isolated atom electron densities placed on the positions the atoms have in the molecule. A maximal conservation of the information of the isolated atoms in the atoms-in-molecules is thereby secured. Atomic charges, atomic dipole moments, and Fukui functions resulting from the Hirshfeld partitioning of the electron density are computed for a large series of molecules. In a representative set of organic and hypervalent molecules, they are compared with other commonly used population analysis methods. The expected bond polarities are recovered, but the charges are much smaller compared to other methods. Condensed Fukui functions for a large number of molecules, undergoing an electrophilic or a nucleophilic attack, are computed and compared with the HOMO and LUMO densities, integrated over the Hirshfeld atoms in molecules.     

Comprehensive quantum chemical calculations and molecular docking analysis of uracil mustard by first principle

Uracil mustard belongs to the nitrogen mustard family and is primarily used in anticancer drugs. The research that follows, investigates many quantum chemical features such as the computation of global minimum energies with no negative wavenumber values using the Density Functional Theory (DFT) with Becke three functional and 6-311G (d, p)/6–311++G (d, p) basis sets. All the vibrational modes have been calibrated and justified in comparison to their experimental counterparts. Mustard's polarizability and hyperpolarizability components, Natural Bond Analysis (NBO), electronic properties, Fukui function analysis, various global parameters, Quantum Theory of Atoms In Molecule (QTAIM) analysis, ADMET analysis, and docking analysis have all been investigated using the same theory and basis sets, indicating its biochemical significance. The biological activity of the molecule is reported by using PASS software. The Full fitness score and binding affinity parameters are utilized to determine the binding strength with 6cq3 protein. The acidity of the title molecule is calculated in water solvent by polarizable continuum model (PCM) solvent effects (estimated in water). The HOMO, LUMO, and MESP plots are used to explore the nature of binding and surfaces. The Fukui functions are computed using Mulliken atomic charges for neutral atoms, cations, and anions. The Ultraviolet–visible (UV–vis) of the molecule is computed employing the TD-DFT method.     

Insights into the binding mechanism of 2,5-substituted 4-pyrone derivatives as therapeutic agents for fused dimeric interactions: A computational study using QTAIM,dynamics and docking simulations of protein–ligand complexes

The study is focused on examining 2,5-Substituted 4-Pyrone based compounds through quantum chemical and topological analysis techniques, evaluating the properties of these compounds, including their geometrical structure, intermolecular interactions and assess their possible applications. Additionally, the molecular stability, charge delocalization and UV-Visible data was investigated and compared with the calculated energy and oscillator strength using the TD-DFT approach. The researchers observed that charge transfer occurred within the molecule, indicated by the HOMO and LUMO energies. It was also found that the compound exhibited planarity and higher chemical reactivity. The calculated Mulliken charges and molecular electrostatic potential were used to interpret the Fukui index data that help predict reactive sites and understand the reactivity patterns of specific atoms in a compound. The study is aimed to understand the role of NCI in the molecule under investigation using electron localization functions and localized orbit locator methods. Molecular docking and ADMET studies were conducting involving a detailed MD simulation of a protein-ligand complex using the OPLS3e force field and the SPC water model. These findings could prove to be beneficial in developing new therapeutic agents with various pharmacological effects and potential toxicities.     

Atom and Bond Fukui Functions and Matrices: A Hirshfeld‐I Atoms‐in‐Molecule Approach

The Fukui function is often used in its atom‐condensed form by isolating it from the molecular Fukui function using a chosen weight function for the atom in the molecule. Recently, Fukui functions and matrices for both atoms and bonds separately were introduced for semiempirical and ab initio levels of theory using Hückel and Mulliken atoms‐in‐molecule models. In this work, a double partitioning method of the Fukui matrix is proposed within the Hirshfeld‐I atoms‐in‐molecule framework. Diagonalizing the resulting atomic and bond matrices gives eigenvalues and eigenvectors (Fukui orbitals) describing the reactivity of atoms and bonds. The Fukui function is the diagonal element of the Fukui matrix and may be resolved in atom and bond contributions. The extra information contained in the atom and bond resolution of the Fukui matrices and functions is highlighted. The effect of the choice of weight function arising from the Hirshfeld‐I approach to obtain atom‐ and bond‐condensed Fukui functions is studied. A comparison of the results with those generated by using the Mulliken atoms‐in‐molecule approach shows low correlation between the two partitioning schemes.     

Theoretical and conformational studies of a series of cannabinoids

The MNDO semi-empirical method is applied to the study of a series of cannabinoids with the aim of providing an improved understanding of the structure-activity relationship (SAR). The conformation of some groups that seem important in the biological activity (psychoactivity) of these compounds is characterized. Some electronic properties, such as atomic net charges and HOMO and LUMO energies, are correlated with the psychoactive effect.     

Application of density functional theory concepts to the study of the chemical reactivity of thiadiazoles

Several useful concepts derived from Density Functional Theory have been applied to study the chemical reactivity of 1,2,5- and 1,3,4-thiadiazoles. Total hardness of the molecules in terms of the HOMO-LUMO gap as a measure of aromaticity and the condensed Fukui functions related to the variations of the net charges of the atoms resulting from a Mulliken population analysis were calculated in order to determine the reactivity of different sites within the molecules studied. The net charges have been obtained from calculations made in the context of the Hartree-Fock-LCAO approximation and the results compared with the existing experimental evidence on thiadiazoles and related compounds.     

Theoretical Study on the Optical Properties for 2,7- and 3,6-Linked Carbazole Trimers by Time-dependent Density Functional Theory

Electronic properties, such as HOMO and LUMO energies, band gaps, ionization potential (IP) and electron affinity (EA) of 2,7- and 3,6-linked carbazole trimers, two conjugated oligomers with different linkages of carbazole, were studied by the density functional theory with Becke-Lee-Young-Parr composite exchange correlation functional (B3LYP). The absorption spectra of these compounds were also investigated by time-dependent density functional theory (TD-DFT) with 6-31G* basis set. The calculated results indicated that the HOMO and LUMO of the 2,7- and 3,6-linked carbazole trimers are both slightly destabilized on going from methyl substitution to sec-butyl substitution. Both IP and EA exhibit their good hole-transporting but poor electron- accepting ability. The presence of alkyl groups on the nitrogen atoms does not affect the intra-chain electronic delocalization along the molecular frame. Thus no significant effect on the band gap and absorption spectra of compounds has been found.     

The effect of electron charge transfer in biological activity and vibrational wavenumbers of 2′-Deoxyuridine and 5-Fluoro-2′-Deoxyuridine: DFT approach

Vibrational analysis of the 2′-Deoxyuridine and 5-Fluoro-2′-deoxyuridine compounds has been performed using FT-Raman and FTIR spectroscopic techniques. The optimized geometry, various bonding features and harmonic vibrational wavenumbers have been computed with the help of B3LYP/6-31G (d, p) density functional theory method. The natural bond orbital analysis, Mulliken population analysis on atomic charges and the HOMO–LUMO energy have been calculated to explore the reasons for the change in biological activity and vibrational wavenumbers of the title compounds. Potential energy distribution analysis has been used to assign the normal modes of vibrations unambiguously.     

Chemical reactivity and selectivity using Fukui functions: basis set and population scheme dependence in the framework of B3LYP theory

The use of Fukui functions for the site selectivity of the formaldehyde molecule for nucleophilic, electrophilic and radical attacks has been made with special emphasis to the dependence of Fukui values on the basis sets as well as population schemes in the framework of B3LYP theory. Out of the five population schemes selected viz., Mulliken population analysis, natural population analysis, CHELP, CHELPG and atoms in molecules (AIM), it is found that the CHELPG and AIM schemes predict precise reactive site with less dependency on the basis sets. Charges derived from Hirshfeld partitioning, calculated using the BLYP/dnd method (implemented in the DMOL³ package), provide non-negative Fukui values for all the molecular systems considered in this study. Supporting results have been obtained for acetaldehyde and acetone molecules at the 6-31+G** basis set level. These results support the fact that high Fukui values correspond to soft–soft interaction sites. On the other hand, the correlation of the low Fukui value to the hard–hard interaction site merits further investigation. Received: 10 November 2001 / Accepted: 6 March 2002 / Published online: 13 June 2002     

马来酸酐均聚反应机理的理论研究Ⅰ: 马来酸酐的基态和激发态电子结构

用AM1方法计算了马来酸酐的基态和激发态电子结构、电荷分布和键级。马来酸酐基态分子的HOMO和LUMO分别是双键C=C的成键π-MO和反键π*-MO。从微观电子结构层次探讨了马来酸酐在不同条件下的均聚反应机理。计算结果能很好地阐明实验事实。