秋水仙碱立体异构体电子结构及圆二色谱性质的理论研究

采用量子化学密度泛函理论(DFT)在B3LYP/6-311++G二水平上对秋水仙碱四个立体异构体分子几何构型进行了优化,在优化的基础上进行了振动圆二色谱(VCD),紫外-可见光谱(UV-Vis)和电子圆二色谱(ECD)研究.为模拟真实条件,以水为溶剂,计算其对分子电子结构和光谱性质的影响.研究结果表明:秋水仙碱四个立体...     

轴手性双蒽醌的分子结构与电子圆二色谱的密度泛函研究

采用从头算密度泛函理论方法,计算了具有轴手性结构的3种双蒽醌分子的电子圆二色谱(ECD),分析了谱带的电子起源以及谱带与分子结构之间的关系.计算结果表明,由于在2,2′位置上的OH取代,导致2个蒽醌基平面之间的不同旋转二面角,使ECD谱具有不同的谱带特征,具有相反的ECD谱.计算的双蒽醌C的谱带形状特征与实验结果基本相符.     

脱羰青蒿素和青蒿素的圆二色谱

含有过氧和内酯基团的青蒿素1是一个结构独特的倍半萜。它的圆二色谱也较特殊,在258nm 和228nm 处分别显示一极大值和一极小值。对此梁晓天提出258nm 处的极大值是一因转折而引起的假象。最近我们以光化学氧化反应高产率地制备了脱羰青蒿素2,     

自旋标记鬼桕类化合物圆二色谱的研究

给已知抗癌药物分子中引入稳定氮氧自由基,合成较母体药物高效低毒的抗癌药物已引起国内外学者的重视.我们在具有抗癌活性的鬼桕毒分子中引入稳定氮氧自由基,药理试验表明其活性保持或增加,而毒性却显著地降低.     

氨基酸修饰的手性多酸的电子结构和光学活性的理论研究

采用密度泛函理论(DFT)方法研究了L-O₂CCHCH₃NH₃(L-Alanine)修饰的手性多酸[Se^ⅣMo₆O₂₁(L-alanine)₃]^2-, [Sb^ⅢMo₆O₂₁(L-alanine)₃]^3-及[Bi^ⅢMo₆O₂₁(L-alanine)₃]^3-的几何结构、电子结构以及紫外-可见(UV-Vis)谱和电子圆二色(ECD)谱.通过对电荷转移跃迁性质的分析, 探讨了多酸中杂原子对手性光学性质的影响.结果表明, 杂原子(Se, Sb, Bi)对多酸的几何结构影响较大, 且对该类体系的UV-Vis谱的吸收峰的强度和峰形都有显著的影响.其ECD谱的转动吸收方向和强度以及吸收峰位和峰形也因杂原子的不同而发生明显变化.低能区UV-Vis谱和ECD谱的产生主要源自多酸中氧原子的p轨道到Mo原子d轨道的电荷转移跃迁, 而对于高能区的UV-Vis谱和ECD谱的产生, 则主要为多酸中杂原子以及与杂原子直接相连的氧原子p轨道到Mo原子d轨道的电荷转移跃迁.     

一种新型联萘基旋光共轭聚合物的圆二色谱和圆偏振荧光光谱

众所周知 ,聚合物的光电性质依赖于聚合物链的构象和 (或 )组成 ,通过在聚合物上引入手性单元 ,采用圆二色谱 ( CD)和圆偏振荧光光谱 ( CPL)等方法可表征聚合物结构 [1] .近年来 ,由于圆偏振光可用作光数据存储和液晶显示器背景光 [2 ] ,人们开始注重共轭聚合物圆偏振光材料的研究 .共轭聚合物的光致和电致圆偏振光的现象由一种带手性侧链的聚噻吩[3 ] 和一种带手性侧链的聚 (对苯撑乙烯 ) [4 ]产生 ,但它们的圆偏振荧光度 (用不对称因子 glum=2 ( IL-IR) / ( IL+IR)表示 ,IL 和 IR 分别指左圆偏振光强度和右圆偏振光强度 )相对较低 …     

免疫算法用于多组分二维色谱数据的解析

通过对免疫系统抗体对抗原消除作用及其记忆功能的模拟,提出了解析二维数据矩阵的新方法。采用模拟的EMG公式作为抗体输入,对二维信号逐行进行迭代消除,从重叠峰中提取单一组分的色谱信息和光谱信息。通过对二维色谱数据的解析,结果表明,该方法可方便地用于多组分重叠二维色谱的解析。     

圆二色谱中的激子手性法在有机化学中的应用

激子手性法是圆二色谱领域内,近一、二十年内发展的一种测定有机化合物绝对构型的可靠方法。本文对其基本原理及规律作一简要介绍。并以邻二醇、共轭烯酮,共轭二烯及丙烯醇为例,介绍本法在测定绝对构型中的应用。此外,本法也可用于糖类的结构研究。     

钕和镧离子对tRNA圆二色谱的影响

采用圆二色谱方法对钕和镧离子与转移核糖核酸间的相互作用进行了研究,结果显示在1.5～6 μmol/L Nd³⁺或La³⁺离子存在下,tRNA分子CD谱260 nm(+)峰蓝移2～3 nm, 260 nm(+)峰值分别增加6%和20%左右;210 nm(-)峰在不同摩尔比Nd³⁺/tRNA作用下,谱峰蓝移或红移,峰值增加或降低50%左右。结果说明结合在tRNA分子上的Nd³⁺或La³⁺可能引起tRNA分子构象的变化。Eu³⁺对大肠杆菌LeuRS或tRNA^Leu-LeuRS复合物的CD谱具有一定的影响。     

圆二色谱研究两个新的呋喃雅槛蓝型倍半萜的绝对构型

前文我们从长梗千里光(Senecio Kaschkarovii)和森林千里光(Senecio Nernenrisis)中分离得到3个10位是羟基的9-氧-呋喃型倍半萜(Ⅰ—Ⅳ),其中Ⅰ和Ⅳ为首次发现的新化合物。这3种化合物A、B环是顺式连接,而6位取代基是β构型,这仅仅是通过它们的核磁共振氢谱与类似化合物对照及NOE差谱确定的。由于此类化合物10位缺少氢,使得用核磁共振氢谱确定A、B环的连接方式尚显论据不足。为进一步证明我们前文的推断的正确性,本文制备     

A circular dichroism detection of stereostructural change due to amine protonation

Aromatic amine conformation can be controlled by protonation and this process can be followed by circular dichroism measurements.     

Circular dichroism studies of bisindole Vinca alkaloids

The analysis of a series of seventeen vinblastine analogs by circular dichroism is described. Exciton coupling of the indole and indoline chromophores of these compounds provides a general, non-empirical method for the assignment of the C16′ configuration with the bioactive C16′-S and the inactive C16′-R analogs giving rise, respectively, to positive and negative couplets. An analysis of the non-coupled transitions of the CDs indicates that a positive Cotton effect at 305 nm, although empirical, is associated with bioactivity. Theoretical calculations of the UV and CD spectra of vinblastine diastereomers are also described.     

Calculation of circular dichroism spectra of michellamines A and C, based on a complete conformational analysis

The first quantum chemical calculation of the circular dichroism (CD) spectra of michellamines has been achieved, based on a complete quantum chemical conformational analysis. Michellamines are dimeric naphthylisoquinoline alkaloids and thus naturally occurring quateraryls, with a large molecular size and flexibility and equipped with stereogenic centers and axes.     

Vibrational circular dichroism of polypeptides and proteins

Vibrational circular dichroism spectra of poly-L-tyrosine, poly-L-phenylalanine, myoglobin and-lactoglobulin were measured in solution for the amide I region. These measurements are shown to be consistent with previous determinations of the secondary structures of these species.     

Absolute configurations of endoperoxides determined by vibrational circular dichroism (VCD)

Diastereomeric mixture on the peroxide portion of an endoperoxide acetylmajapolene A (1) was efficiently separated by HPLC on a chiral column, submitting to vibrational circular dichroism (VCD) investigation. The ab initio theoretical VCD and IR calculations of 1a and 1b were performed by density functional theory (DFT) using the B3PW91/6-31G(d,p) level of theory. Focusing on an isolated characteristic peroxide vibrational band, absolute configurations of 1a and 1b were unambiguously determined as (1R,4R,7S,10S) and (1S,4S,7S,10S), respectively. This is the first VCD application to endoperoxides which exist abundantly in nature.     

A vibrational circular dichroism implementation within a Slater-type-orbital based density functional framework and its application to hexa- and hepta-helicenes

We describe the implementation of the rotational strengths for vibrational circular dichroism (VCD) in the Slater-type orbital based Amsterdam Density Functional (ADF) package. We show that our implementation, which makes use of analytical derivative techniques and London atomic orbitals, yields origin independent rotational strengths. The basis set dependence in the particular case of Slater-type basis functions is also discussed. It turns out that the triple zeta STO basis sets with one set of polarization functions (TZP) are adequate for VCD calculations. The origin- dependence of the atomic axial tensors is checked by a distributed origin gauge implementation. The distributed and common origin gauge implementations yield virtually identical atomic axial tensors with the Slater-type basis sets employed here, proving that our implementation yields origin independent rotational strengths. We verify the implementation for a set of benchmark molecules, for which the dependence of the VCD spectra on the particular choice of the exchange–correlation functional is studied. The pure functionals BP86 and OLYP show a particularly good performance. Then, we apply this approach to study the VCD spectra of hexa- and hepta- helicenes. In particular we focus on relationships between the sign of the rotational strengths of the two helicenes. Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.     

Origin‐independent sum over states simulations of magnetic and electronic circular dichroism spectra via the localized orbital/local origin method

Although electronic and magnetic circular dichroism (ECD, MCD) spectra reveal valuable details about molecular geometry and electronic structure, quantum‐chemical simulations significantly facilitate their interpretation. However, the simulated results may depend on the choice of coordinate origin. Previously (?těpánek and Bou?, J. Comput. Chem. 2013, 34, 1531), the sum‐over‐states (SOS) methodology was found useful for efficient MCD computations. Approximate wave functions were “resolved” using time‐dependent density functional theory, and the origin‐dependence was avoided by placing the origin to the center of mass of the investigated molecule. In this study, a more elegant way is proposed, based on the localized orbital/local origin (LORG) formalism, and a similar approach is also applied to generate ECD intensities. The LORG‐like approach yields fully origin‐independent ECD and MCD spectra. The results thus indicate that the computationally relatively cheap SOS simulations open a new way of modeling molecular properties, including those involving the origin‐dependent magnetic dipole moment operator. © 2015 Wiley Periodicals, Inc.     

Frenkel‐exciton decomposition analysis of circular dichroism and circularly polarized luminescence for multichromophoric systems

Recently, a method to calculate the absorption and circular dichroism (CD) spectra based on the exciton coupling has been developed. In this work, the method was utilized for the decomposition of the CD and circularly polarized luminescence (CPL) spectra of a multichromophoric system into chromophore contributions for recently developed through‐space conjugated oligomers. The method which has been implemented using rotatory strength in the velocity form and therefore it is gauge‐invariant, enables us to evaluate the contribution from each chromophoric unit and locally excited state to the CD and CPL spectra of the total system. The excitonic calculations suitably reproduce the full calculations of the system, as well as the experimental results. We demonstrate that the interactions between electric transition dipole moments of adjacent chromophoric units are crucial in the CD and CPL spectra of the multichromophoric systems, while the interactions between electric and magnetic transition dipole moments are not negligible. © 2018 Wiley Periodicals, Inc.     

Stereochemical assignments of 22-isoxazolinylsteroids using circular dichroism

Circular dichroism (CD) spectra of 22-hydroxy- and 22-acetoxy-22-isoxazolinylsteroids were studied. The configuration of the C-5′ center of the heterocycle was established from the sign of the n-π*-transition band of the azomethine chromophore. The band molecular ellipticity was shown to depend on the mutual placement of the isoxazoline ring and the steroid skeleton of the studied compounds. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 495–499, September-October, 2008.