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3.
The crystal structures of known anthra-tetrathiophene (ATT) and its three fluorinated derivatives (ATT1, ATT2 and ATT3) were predicted by the Monte Carlo-simulated annealing method with the embedded electrostatic potential (ESP) charges. The most stable crystal structures were further optimized by the density functional theory with the dispersion energy (DFT-D) method. In addition, the effect of the electron-withdrawing fluorine atoms on the molecular geometry, molecular stacking, electronic and transport properties of title compounds were investigated by the density functional theory and the incoherent charge-hopping model. The calculated results show that the introduction of fluorine atoms does not affect the molecular planarity but decreases the HOMO-LUMO gap, which is beneficial to electron injection and provides more charge carrier stabilization. The improved electron mobility from ATT to ATT3 is attributed to the favorable molecular packing with strong π–π interaction and the short stacking distance. ATT2 and ATT3 exhibit remarkable angular dependence of mobilities and anisotropic behaviors. The band structures reveal that all the paths with larger transfer integrals are along the directions of large dispersions in the valence band (VB) and conduction band (CB). ATT3 has the largest electron mobility (0.48 cm2 V−1 s−1) among the four compounds, indicating that fluorination is an effective approach to improve electron transport. 相似文献
4.
Saccharopine dehydrogenase (SDH) is the last enzyme in the AAA pathway of l-lysine biosynthesis. On the basis of crystal structures of SDH, the whole catalytic cycle of SDH has been studied by using density functional theory (DFT) method. Calculation results indicate that hydride transfer is the rate-limiting step with an energy barrier of 25.02 kcal/mol, and the overall catalytic reaction is calculated to be endothermic by 9.63 kcal/mol. Residue Lys77 is proved to be functional only in the process of saccharopine deprotonation until the formation of product l-lysine, and residue His96 is confirmed to take part in multiple proton transfer processes and can be described as a proton transfer station. From the point of view of energy, the SDH catalytic reaction for the synthesis of l-lysine is unfavorable compared with its reverse reaction for the synthesis of saccharopine. These results are essentially consistent with the experimental observations from pH dependence of kinetic parameters and isotope effects. 相似文献
5.
Flavonoids are a large group of polyphenolic compounds ubiquitously present in plants. They are important components of human diet. They are recognized as potential drug candidates to be used in the treatment and prevention of a lot of pathological disorders, due to their protective effects. Baicalin (7-glucuronic acid 5, 6-dihydroxyflavone) is one of the main single active constituents isolated from the dried roots of Scutellaria baicalensis Georgi. The great interest on this flavonoid is due to its various pharmacological properties, such as antioxidant, antimicrobial, anti-inflammatory, anticancer and so on, and its high accumulation in the roots of S. baicalensis. The aim of our work was to analyze the geometric and electronic properties of baicalin conformers (BCL), thus performing a complete search on the conformational space of this flavonoid in gas phase and in aqueous solution. The results indicate that the conformational space of baicalin is formed by eight conformers in gas phase and five conformers in aqueous solution optimized at B3LYP/6-311++G** theory level. BCLa2TT and BCLa1TT conformers have low stability in gas phase and very high stability in aqueous solution. This variation is related to a modification in the τ1 angle that represents the relative position of the glucuronide unit respect to the central rings of the flavan nucleus (A and C). This modification was successfully explained by examining the changes in the hydrogen bond (HB) interactions that occur in the region around the hydroxyl group located in position 6 of ring A. Besides, the molecular electrostatic potential (MEP) and frontier molecular orbital (FMO) analyses indicate that BCLa2TT and BCLa1TT conformers are the most favorable conformers for interacting with positively charged species (such as metal ions) in aqueous media (such as biological fluids). 相似文献
6.
用密度泛函理论研究了HNO OH反应机理。在(U)B3LYP/aug-cc-pVTZ水平上,优化了反应通道上各驻点(反应物、中间体、过渡态和产物)的几何构型,获得了零点能校正后的反应势能曲线。研究表明:根据进攻方式的不同,有3个反应通道,反应通道不同则产物不同。反应的主要产物是NO H_2O,次要产物是NH_2 O_2;主要产物和次要产物与反应物的总能量之差(经零点能校正后)分别为-133.42 kJ/mol和150.44 kJ/mol。生成主要产物时主要反应通道的活化能为102.11 kJ/mol。 相似文献
7.
本文从理论上对丙烯酸正丁酯(nBA)自引发聚合的Diels-Alder反应机理进行了研究.利用DFT方法在UB3LYP/6-31G*水平上对反应的最低能量路径进行了计算,各驻点能量分别采用MP2/6-311G**和B3LYP/6-311 G(3df;2p)进一步精确计算.结构表明:此Diels-Alder反应仅包括一种途径,即路径(I),另一条途径在热力学不支持. 相似文献
8.
为了确定STO-3G、3-21G、6．31G三个基组是否适用于7-氨基-3-去乙酰基头孢烷酸(简称7-ADCA),以及计算其热力学函数,本文用密度泛函理论的B3LYP方法分别在STO一3G、3-21G、6—31G水平上对7一ADcA进行红外光谱计算、能量计算和结构优化。将得到的三组红外光谱波数与实验值进行比较分析,发现3—21G和6—31G基组得到的数据比较可靠。得到的能量参数用于计算7一ADCA的一些热力学函数,例如标准生成热、生成吉布斯自由能和标准熵,并对结果进行校正。比较三个基组优化出的7-ADCA的结构,发现3—21G和6—31G基组得到的结果相近,而与STO．G相比有一些出入。这些分析结果有助于7-ADCA合成头孢药物的研究。 相似文献
9.
1, 4, 7, 10-tetraazacyclododecane-1, 4, 7, 10-tetracetic acid (DOTA) is an important chelator for radiolabeling of pharmaceuticals. The ability of alkali metals found in the body to complex with DOTA and compete with radio metal ions can alter the radiolabeling process. Non-covalent interactions between DOTA complexed with alkali metals Li+, Na+, K+ and Rb+, are investigated with density functional theory using B3LYP and ωB97XD functionals. Conformational possibilities of DOTA were explored with a varying number of carboxylic pendant arms of DOTA in close proximity to the ions. It is found that the case in which four arms of DOTA are interacting with ions is more stable than other conformations.The objective of this study is to explore the electronic structure properties upon complexation of alkali metals Li+ Na+, K+ and Rb+ with a DOTA chelator. Interaction energies, relaxation energies, entropies, Gibbs free energies and enthalpies show that the stability of DOTA, complexed with alkali metals decreases down the group of the periodic table. Implicit water solvation affects the complexation of DOTA―ions leading to decreases in the stability of the complexes. NBO analysis through the natural population charges and the second order perturbation theory, revealed a charge transfer between DOTA and alkali metals. Conceptual DFT-based properties such as HOMO/LUMO energies, ΔEHOMO-LUMO and chemical hardness and softness indicated a decrease in the chemical stability of DOTA―alkali metal complexes down the alkali metal series. This study serves as a guide to researchers in the field of organometallic chelators, particularly, radiopharmaceuticals in finding the efficient optimal match between chelators and various metal ions. 相似文献
10.
基于定量结构-活性相关（QSAR）研究氯代芳烃的性质具有重要意义。对22种氯代芳烃化合物进行DFT-B3LYP/6-311G**水平全优化计算。据所得量子化学参数建立氯代芳烃对戈卑鱼急毒性(-IgLC50)的QSAR模型。对训练集样本经逐步多元回归分析后,所建QSAR模型的复相关系数R2及去一法（LOO）交互检验复相关系数R2cv分别为0.963和0.962,用预测集样本进行了外部预测,所得外部预测样本复相关系数R2ext和外部预测集交互检验Q2ext分别为0.968和0.820,表明所建立的QSAR方程具有较好的稳定性和预测能力。模型结果表明:氯代芳烃化合物的毒性与分子总能量（Eγ）、分子体积（V）及分子次最低空轨道能(ENLUMO)的相关性较好。 相似文献
11.
用16种脂肪胺类化合物HF/6-31G**,HF/6-311G**,DFT-B3LYP/6-31G**和DFT-B3LYP/6.311G**全优化计算结构参数:分子最高占用和最低空轨道能(EHOMO和ELUMO),分子次最高占用和次最低空轨道能(ENHOMO和ENLUMO),分子总能量(ET),氢原子所带的最高正电荷(qH+),最负原子的静电荷(q-),分子偶极矩(μ)和分子体积(V),对它们的脂水分配系数(lgKOW)分别进行定量构效关系(QSPR)研究.结果表明:脂肪胺的lgK与分子最低空轨道能(ELUMO),分子的总能量(ET)和分子偶极距(μ)的相关性较好,成功地建立了lgKOW的QSPR方程.特别是基于B3LYP/6-311G**基组建立的方程具有更好的[[预]能力,并通过VIF值和t值对其稳健性进行了检验,结果良好. 相似文献
12.
对35种硝基芳烃化合物进行DFT-B3LYP/6-311G**水平全优化计算。据所得量子化学参数和标题化合物的辛醇/水分配系数(IgKOW)建立硝基芳烃对黑头呆鱼毒性(-IgLC50)的QSAR模型,采用内部及外部双重验证的办法深入分析和检验模型的稳健性。最佳模型的复相关系数（R2）,去一法（LOO）交互检验复相关系数(R2cv),外部预测样本复相关系数(R2ext)分别为0.975,0.970和0.904,故所建立QSAR模型的稳定性和预测能力良好。结果表明:硝基芳烃化合物的毒性主要由分子最低空轨道能(ELUMO)、硝基静电荷(QNO2)、氢原子所带的最高正电荷（QH+）及辛醇/水分配系数决定。苯环上取代基的类型、数目和取代位置直接影响到标题化合物的毒性大小,强吸电子基如硝基会使化合物毒性增强,且邻对位硝基取代的毒性高于间位取代;相反,给电子基团氨基的存在则会使化合物的毒性降低。总之,硝基是这类化合物致毒的主要基团,将硝基包覆或还原为氨基应为此类化合物解毒的重要途径。 相似文献
13.
多溴苊是一类潜在的有机污染物。本文采用密度泛函理论在B3LYP/6-311G**水平上优化35个多溴苊化合物的分子几何结构,并获得它们在理想气态的一些热力学性质的数值,研究这些性质与取代的溴原子数目和位置的关系,根据各异构体的标准生成Gibbs自由能的相对大小,求得它们的热力学稳定性顺序。计算结果表明:在大部分多溴苊分子中,除4个氢原子外的其他原子在同一平面上。多溴苊最稳定及最不稳定异构体的ΔfH及ΔfG,都随Br原子数目增加而逐渐增加。溴原子数目相同的多溴苊异构体的ΔfH和ΔfG与溴原子的取代位置有很大的关系,其相对稳定性主要由分子内的处在不同六元环上的邻近Br...Br核排斥作用决定。所有多溴苊化合物在热力学上都比其母体化合物苊相对较难形成。 相似文献
14.
几种新型双吡唑衍生物缓蚀性能的理论研究 总被引：1，自引：0，他引：1
通过量子化学计算中的密度泛函理论(DFT)/B3LYP方法在6-311+G(d,p)水平上对3种新型双毗唑衍生物5,5'-二甲基-4-乙酯基-1'氢-1,3'-二吡唑(Bipl)、1,1',5,5'一四甲基-1氢,1'氢-3,3'-二吡唑(Bip2)和3-(溴甲基)-5,5'-二甲基-1'氢-1,3'-二吡唑(Bip3)的缓释性能与结构关系进行了研究。用Fukui指数分析了分子中反应活性位点。结果表明全局活性参数最高占据轨道能量(E_(HOMO))、偶极矩(μ)、电负性(X)及电子转移数(△N)与缓释性能有良好的关系。缓蚀性能的理论评价结论与实验结果相吻合。 相似文献
15.
基于定量结构.活性(QSAR)研究取代酚类化合物的急毒性具有重要意义。采用DFT-B3LYP方法,在较高基组6-311G~(**)水平下,全优化计算21种取代酚。从中获得分子最高占用和最低空轨道能(E_(HOMO)和E_(LUMO))、分子次最高占用和次最低空轨道能(E_(NHOMO)和E_(NLUMO))、分子总能量(E_T)、氢原子所带的最高正电荷(q_H~+)、最负非氢原子的静电荷(q~-)、分子偶极矩(μ)和分子体积(V)等描述符。结合文献中标题化合物对梨形四膜虫的毒性值(-lg LC_(50))和疏水性系数(10g Kow),由多元线性回归方法建成QSAR模型,采用内外双重验证的办法,深入分析和检验模型的稳健性。最佳模型的复相关系数(R~2),去一法(LOO)交替检验复相关系数(R_(cv)~2),外部预测样本复相关系数(R_(ext)~2)分别为0.924,0.922和0.830,故所建QSAR模型的稳定性和预测能力良好。由此推断,标题物对梨形四膜虫的毒性作用分为两步,首先穿过细胞壁在细胞内富集,以log Kow描述;其次与亲核试剂发生亲电反应,以点E_(NLUMO)表示。 相似文献
16.
基于定量结构-活性相关（QSAR）研究酚类化合物的急毒性具有重要意义。运用DFT-B3LYP方法,在较高基组6-311G**水平下,全优化计算25种取代酚。从中获得分子最高占用和最低空轨道能(EHOMO和ELUMO)、前线轨道能级差(AE=EHOMOˉ尻LUMO)、分子次最高占用和次最低空轨道能(ENHOMO和ENLUMO、分子总能量（ET）、氢原子所带的最高正电荷（qH+）、最负非氢原子的静电荷（g）、分子偶极矩（μ）和分子体积（V）等描述符。结合文献中标题化合物对黑头呆鱼急毒性值(-1g LC50),由多元线性回归方法建成QSAR模型,采用内外双重验证的办法,深入分析和检验模型的稳健性。最佳模型的复相关系数（R2）,去一法（LOO）交替检验复相关系数(R2CV),外部预测样本复相关系数(R2ext)分别为0.976,0.974和0.940,故所建QSAR模型的稳定性和预测能力良好。表明:取代酚对黑头呆鱼急毒性与分子体积、最负非氢原子的静电荷及分子总能量的相关性密切。 相似文献
17.
本文应用量子化学密度泛函理论(DFT)研究了2-(4-甲氧基苯基)亚肼基乙酸与乙醛酸的反应机理及动力学行为,并研究了不同取代基对反应的影响.在RB3LYP/6-31G*水平上,优化了各反应通道的反应物、中间体、过渡态及产物的几何构型,计算了各驻点的振动频率、零点能和电荷分布.计算结果表明,该反应有2条反应通道,分别生成(2Z)和(2E)-3(4-甲氧基苯基二氮烯基)丙烯酸.产物发生了键长的平均化和电荷的重新分布.两反应通道具有相同的反应入口,Z式产物为主要产物,2-(4-甲氧基苯基)亚肼基乙酸中苯环对位被给电子基团取代,有利于反应进行. 相似文献
18.
P-ZSM-5分子筛通常用来催化甲醇转化制轻烯烃,乙醇脱水制乙烯,芳烃的烷基化或者歧化等反应。目前,P-ZSM-5分子筛中磷和分子筛之间的相互作用仍不清楚。本文通过密度泛函理论（Density Functional Theory,DFT）计算了ZSM-5分子筛改性前后的结构及酸性变化。结果发现P骨架外改性后,磷酸分子的氢原子和分子筛骨架氧原子形成氢键作用,并且O4,Ha和0zeo总是保持在一条直线上,这是稳定的骨架外改性结构;骨架改性后,分子筛优化前后的结构发生较大变化,这是因为固定了8T模型中的终止氢原子,分子筛的骨架结构阻止了H2PO3基团的插入。本文还计算了磷酸分子和分子筛的酸性位之间的关系,研究发现,分子筛中引入P后,其酸性降低,且骨架改性后酸性减弱的程度更大。这一结果可以进一步指导实验,制备出不同酸性的分子筛。 相似文献
19.
孙丽 《计算机与应用化学》2012,29(3):360-364
采用密度泛函理论的B3LYP方法在6-311++G**基组水平上优化了,用等电子体-CH-基团逐个取代N8H8环状异构体中最稳定的分子构型中的N原子,得到32种Nn（CH）8-nH8（n=0-7）的异构体,应用自然键轨道理论NBO和分子中的原子理论AIM分析了这些化合物成键特征和相对稳定性,G3MP2方法计算了各异构体的能量及生成热。研究结果表明:N原子孤对电子到相邻的碳氮键的超共轭作用是影响碳氮键长变化的主要因素;随着等电子体-CH-基团取代分子中氮原子的个数的增加,分子的生产热逐渐减小,而分子的能量将逐渐升高,且有很好的线性相关性。 相似文献
