槲皮素抗氧化活性的密度泛函理论研究

采用杂化密度泛函理论(DFT)方法, 预测了黄酮类化合物槲皮素分子的几何结构、电子结构和脱氢解离焓, 分析了这些性质与分子活性位的关系, 探讨了槲皮素分子的抗氧化活性, 即与活性氧自由基•OH, •OOH和 的反应机理. 在B3LYP/6-31＋G(d)水平下, 计算得到的槲皮素分子脱氢自由基的相对稳定性、脱氢解离焓和氢提取过程的活化能都表明, 槲皮素中的4 -羟基活性最高, 最有可能参与自由基的清除. 4 -羟基位的这种反应活性主要来源于相邻羟基之间的弱氢键相互作用. 深入研究槲皮素分子的抗氧化机理, 有助于更合理地设计和合成新的抗氧化剂.     

富勒烯结构B_(80)分子静电势的理论研究

在混合密度泛函B3LYP理论下,用6-31G*基函数对富勒烯结构B80分子的3个异构体(1个具有Ih对称性,2个具有Th对称性)构型进行优化和分子静电势计算.结果表明:3个异构体球内全部为正电势,球外五元环中心所对应的区域都为负电势,B80Ih,Th(A)和Th(B)球外静电势的最大负值分别对应于20个六元环中心的B原子,五元环中心和12个六元环中心的B原子周围,它们组成了化学反应中最可能的活性点.     

3种黄酮醇ESI-ITMS准分子离子构型的密度泛函理论分析

采用密度泛函理论(Density functional theory,DFT)B3LYP方法,通过全几何结构优化、二面角柔性势能扫描,对山奈酚、槲皮素、杨梅素3种黄酮醇分子的优势构象及电喷雾离子阱质谱(ESI-ITMS)负离子模式下准分子离子的最优构型进行了研究,并从能量参数、构型参数、质谱实验角度对准分子离子的最优构型作出了确证。结果表明:山奈酚、槲皮素和杨梅素分子二面角D(1,2,1',6')均接近0°,分子的优势构象均为B环与A,C环处在同一平面上的构象;在负离子模式下,自动及手动扫描方式得到的山奈酚、槲皮素、杨梅素的二级质谱的复杂程度依次减弱,各分子失去羟基氢所形成的准分子离子结构共轭链增长、共轭效应加强;山奈酚存在两种低能量的准分子离子构型,即失去B环4'位羟基氢与失去A环7位羟基氢的构型,槲皮素与杨梅素失去B环4'位羟基氢的总能量最低、构型最稳定,且山奈酚、槲皮素、杨梅素准分子离子构型的稳定性依次增加。该研究可供进一步探索黄酮醇类化合物ESI-ITMS负离子模式下的质谱裂解规律参考。     

靛玉红及其异构体构效关系的密度泛函理论研究

采用密度泛函理论(DFT)方法计算了靛玉红及其异构体分子的几何构型、电子结构以及前线分子轨道等,研究了结构与抗癌活性之间的关系,探讨了其构效关系上的差异.结果表明,分子是否具有平面构型和广泛共轭体系、3′位C原子的净电荷、分子偶极矩等参数的差异是影响各异构体药效的主要因素.提高3′位C原子的负电荷和增大分子偶极矩将有助于提高化合物的抗癌活性.     

1，5—苯并硫氮杂Zuo氯代β—内酰胺衍生物的合成、光谱及立体化学

苯并硫氮杂Zuo是一类具有重要生理活性的七元杂环化合物,近年来,通过亚胺双键（C＝N）的环加成反应向此类化合物分子中引入新的环系引起了它们的关注^[1-4]。这项工作对于合成新的杂Zuo类化合物从而筛选出具有特殊生理活性的物质有着重要意义。本文通过1,5－苯并硫氮杂Zuo与氯乙烯酮的反应向原分子中并合一个β－内酰胺活性单元,合成了一系列新型的1,5－苯并硫氮杂Zuo-α氯代－β－内酰胺衍生物（B1－B5）,研究了它们的波谱特征及立体结构。     

N8H8环状异构体的结构与稳定性的理论研究

采用密度泛函理论的B3LYP方法在6-311 G**基组水平上对N8H8氮氢环状化合物可能存在的构型进行了几何优化,得到74种稳定异构体,应朋A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方法汁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氮氮键的超共轭作用是影响氮氮键长变化的丰要因素;N8H8环状异构体的稳定性顺序为:六元环>七元环>八元环,五元环>三元环>四元环,六元环是这些N8H8环状异构体中最稳定的,最不稳定的是四元环,G19是所有环状异构体中能量最低的:M3能量最高,稳定性最差,A7密度最大.     

蒲公英黄酮抗氧化活性的构效关系分析

蒲公英作为传统的中药材,具有抗氧化、抗肿瘤、抗菌、抗炎等多种药用价值。黄酮是蒲公英发挥抗氧化作用的重要活性成分。蒲公英黄酮抗氧化性能的实验研究备受关注,然而从分子水平对蒲公英黄酮结构与抗氧化活性之间的内在关系缺乏系统的研究。本文借助于密度泛函理论,针对蒲公英中5种重要的黄酮化合物(槲皮素、芦丁、木犀草素、芹菜素、香叶木素),通过优化结构参数、捕获DPPH自由基的热力学能量分析,NBO电荷分布、半醌自由基的自旋密度分析等方面深入探讨了蒲公英黄酮化合物抗氧化活性的构效关系及内在规律。结果表明：5种蒲公英黄酮化合物抗氧化活性为芦丁>槲皮素>木犀草素>>香叶木素>芹菜素,酚羟基的位置是影响蒲公英黄酮抗氧化活性差异的主要因素。蒲公英黄酮不同位点抗氧化活性的高低与其酚羟基上H原子的电荷分布、黄酮自由基的稳定性成正比关系,自由基单电子的离域程度和分子内氢键的稳定化作用共同决定了B环4’-OH是蒲公英黄酮的关键活性位点。     

槲皮素-3-O-丙基衍生物的合成及生物活性研究

槲皮素是具有丰富生物活性的黄酮类化合物,药理活性显著。本文以槲皮素为先导物,选择性对C环3位羟基进行修饰,以廉价的芦丁为原料,经苄基保护、Williamson成醚反应,再经Pd/C催化加氢脱苄基得到28个未见文献报道的槲皮素-3-O-丙基衍生物,其结构经¹H NMR、¹³C NMR、ESI-MS进行确证。采用MTT法考察了所合成化合物对人食管鳞癌（EC109）、人胃癌（HGC27）、人乳腺癌（MCF-7）、小鼠黑色素瘤（B16-F10）的增殖抑制作用。结果显示,通过化学方法对槲皮素结构进行修饰后,其体外抗肿瘤活性增强。其中,化合物F3(IC₅₀=5.23±0.37μmol/L)、F5(IC₅₀=2.63±0.09μmol/L)对小鼠黑色素瘤（B16-F10）抑制作用比5-氟尿嘧啶(IC₅₀=14.38±0.27μmol/L)好,值得进一步研究。     

Hirsutellide A立体异构体的单晶结构与抗分支杆菌生物活性研究

研究了hirsutellide A立体异构体的X衍射单晶结构及其抗分支杆菌活性. 该化合物具有扭曲马鞍型18元大环结构; 在体外生物活性测试中, 化合物未表现出明显的抗分支杆菌活性. 由实验结果可以看出在天然环酯肽hirsutellide A中3'-C手性中心是其生物活性关键位点之一.     

2-酰基-1,3-环二酮类化合物互变异构的理论计算

采用MP2/6-31+G**//B3LYP/6-31+G**方法,系统地研究了2-酰基-1,3-环二酮类化合物的互变异构性质,探讨了环的饱和性、环的大小、环上杂原子以及溶剂效应对各互变异构体相对稳定性的影响。结果表明:(1)未烯醇化的异构体由于无法形成分子内氢键而具有较高的能量;(2)环上杂原子的推电子效应提高了邻位羰基氧上的负电荷,从而有利于相应环外烯醇式异构体的稳定;(3)对化合物3-酰基-1H-吡啶-2,4-二酮,3-酰基吡喃-2,4-二酮,2-酰基环戊-4-烯-1,3-二酮和3-酰基吡咯-2,4-二酮,由互变异构形成的环的芳香性在各异构体的相对稳定性中扮演着决定性的作用。     

Structure and PMR spectra of isoquercitrin and hirsutrin

Chemistry of Natural Compounds - 1. Two isomers of quercetin 3-glucoside are present in the flowers and leaves of the cotton plant of variety 108-F: hirsutrin, quercetin 3-β-D-glucopyranoside;...     

Density functional computations of the energetic and spectroscopic parameters of quercetin and its radicals in the gas phase and in solvent

Quercetin and its radicals were investigated at the B3LYP density functional level with the aim of determining the energetic and spectroscopic parameters and the factors that influence their antioxidant activity in the gas phase and in aqueous solution. The results indicated that the antioxidant ability of quercetin is mainly due to the orthodiphenolic moiety but also to the presence of the C=C double bond of the pyrone ring. Differences in the stability order of the isomers of quercetins radicals were found in going from vacuum to solvent. Hyperfine coupling constants were computed to help the interpretation of the intricate ESR spectrum of quercetin.Contribution to the Jacopo Tomasi Honorary Issue     

槲皮素与尿嘧啶和胸腺嘧啶氢键的结合位点

深入理解药物分子和核酸碱基间的相互作用机制对合理设计研发新型高效药物有重要意义. 本文运用密度泛函理论B3LYP方法对核酸碱基尿嘧啶和胸腺嘧啶与药物分子槲皮素间的氢键相互作用位点进行了研究. 使用B3LYP/6-31G(d)方法优化得到了30个稳定的氢键复合物结构, 使用B3LYP/6-311++G(3df,2p)方法计算了这些复合物的结合能. 研究结果表明, 槲皮素可以使用5个不同的结合位点与尿嘧啶或胸腺嘧啶形成氢键复合物, 尿嘧啶或胸腺嘧啶可以使用3个不同的结合位点与槲皮素形成氢键复合物. 当槲皮素的结合位点固定时, 槲皮素与尿嘧啶的位点u1或胸腺嘧啶的位点t1形成的氢键作用最强, 与位点u2或位点t2形成的氢键强度最弱; 当尿嘧啶或胸腺嘧啶的作用位点固定时, 二者与槲皮素的位点qu1 形成的氢键作用最强, 与位点qu5 作用强度次之, 与位点qu3的作用强度最弱. 分子中原子(AIM)和自然键轨道(NBO)分析计算结果表明, 轨道作用在氢键中起重要作用.     

Novel quercetin derivatives: synthesis and screening for anti-oxidant activity and aldose reductase inhibition

The direct acylation of quercetin (I) with 3-chloro-2,2-dimethylpropanoyl chloride (II) gives a complex reaction mixture. The synthesis of different acylated quercetin with from mono- to tetra-O-substituted functions was achieved in a simple procedure wherein the yield of isomers depended on the stoichiometric ratio of reagents. The crude reaction mixtures were analysed (LC-MS) and compared with the isolated products. Unambiguous structural characterisation of isomeric quercetin derivatives was confirmed by NMR analysis. In addition, the quercetin dimer can be obtained in a high yield in the simple procedure. The anti-oxidant activity and aldose reductase inhibition of the compounds were screened with the aim of providing bi-functional remedies to treat diabetic complications and other diseases where oxidative stress and the polyol pathway are key etiological factors.     

Super-valence phenomenon of carbon atoms in C20 molecule

Fourteen structures of C₂₀ are studied at DFT/B3LYP/6-31G* theoretical level. Except ring, bowl, cage and isomer 1 which have been studied before, other isomers have not been reported so far. Calculated results show that the ring has the lowest energy at this level and isomers 1, 2, 3 and 4 have lower energies than that of cage. Analyses of optimized bond lengths, electronic structure indicate that some carbon atoms express super-valence property. In addition, NICS value is consistent with molecular orbital character in denoting aromaticity of C₂₀ molecule. Delocalization character averts influence of curvature strain, which can well explain the stability of the cage.     

Theoretical study of structure, vibrational frequencies, and electronic spectra of polychlorinated dibenzo-p-dioxins

The structure, vibrational frequencies, and excited states of 2,3,7,8-tetrachloro-, 1,4,6,9-tetrachloro-, and octachlorodibenzo-p-dioxin (2,3,7,8-TCDD, 1,4,6,9-TCDD, and OCDD) were studied via complete active space SCF followed by the multireference second-order perturbative approach (CASSCF/CASPT2), as well as the time-dependent density functional theory (TD-B3LYP). The cc-pVDZ basis set and the full pi-electron active spaces of 16 electrons in 14 active orbitals were employed. Whereas 2,3,7,8-TCDD assumes a planar D(2)(h)() minimum, 1,4,6,9-TCDD and OCDD are slightly folded exhibiting the C(2)(v)() symmetry. The extra stabilization due to the folding is very small. In all three isomers the highly intensive band system in the 200-240 nm region is dominated by the transitions to the 2(1)B(2u) and 3(1)B(2u) states with by far the largest oscillator strengths. The low-intensity absorptions in the 280-320 nm region can be attributed to the 1(1)B(2u) <-- 1(1)A(g), with possible contribution of the vibronically allowed 2(1)A(g) <-- 1(1)A(g) transition. Both CASPT2 and TD-B3LYP convincingly predict 1(3)B(3g) to be the lowest lying triplet state, which contradicts the experimental assignments. Calculated harmonic wavenumbers and absorption spectra agree well with the experimental data, and are sufficiently distinct to allow for an unambiguous identification of the three isomers.     

Comparing the Affinities of Flavonoid Isomers with Protein by Fluorescence Spectroscopy

Abstract

Dietary flavonoids can be detected in plasma as protein‐bound conjugates. Flavonoids–protein interaction is expected to modulate the bioavailability of flavonoids. In this work, the binding flavonoid isomers (galangin, baicalein, apigenin, and genistein; MW=270.25) and B‐ring hydroxylation flavonols (galangin, kaempferol, quercetin, and myricetin, which share the same structure on the A and C rings but have 0, 1, 2, and 3 moieties of ‐OH on the B‐ring, respectively) to protein were investigated by fluorescence quenching method. The apparent binding constants (K _a ) of were flavonoid isomers determined as: flavones (10⁶–10⁷ L mol^?1)>isoflavone≈flavonol (10⁵ L mol^?1). For B‐ring hydroxylation flavonols, the binding affinity increased with increasing number of hydroxyl groups on the B‐ring. The binding constants (K _a ) were determined as follows: myricetin>quercetin>kaempferol>galangin.     

溴代作用对竹红菌乙素分子性质影响的量子化学研究

用半经验量子化学方法AM1和PM3对竹红菌乙素及其溴代物进行了对比计算,考察了溴代作用对竹红菌乙素分子性质的影响。两种方法所得结果均表明,溴代作用使分子的生成热、前线轨道能级及偶极矩等参数都有所降低,溴代作用也影响了竹红菌乙素分子内氢键的性质,并能使其对光的吸收产生红移。     

Theoretical study on the structures and stabilities of the isomers of N6H6

Forty-eight possible isomers of N₆H₆ have been investigated at the B3LYP/6-311++G^** and G3B3 levels. The results show that heats of formation of all isomers are positive and A2-3 is the lowest and C2 is the highest. In addition, the energies and the heats of formation of the ring-shaped isomers are higher than those of the chain-shaped isomers. Among the ring-shaped isomers, the four-membered ring isomers have the highest heat of formation and the five-membered ring isomers have the lowest. For six-membered ring isomers, only the chair-shaped isomers are stable. Among all those chain-shaped isomers, the ones which have N–N bond and its length is in the range of NN double bond can improve the stability of the compounds.     

Synthesis and structural study of thiacyclophanes utilizing dibromides and methane dithiolate

The synthesis of a series of thiacyclophanes and optically active binaphthol-based chiral thiacyclophanes is reported with XRD structure. Two diastereomeric tetrathiacyclophanes are designed and synthesized. The two diastereomers are evidenced by crystal structure; the single-crystal X-ray studies reveal that one of the isomers possesses an inherent property of self-assembling into a vertical stack of tunnel-like structures.