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首页> 外文期刊>The journal of physical chemistry, B. Condensed matter, materials, surfaces, interfaces & biophysical >Theoretical Modeling of Electronic Structures of Polyiodide Species Included in alpha-Cyclodextrin
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Theoretical Modeling of Electronic Structures of Polyiodide Species Included in alpha-Cyclodextrin

机译：α-环糊精中包含的聚碘公司物种电子结构的理论建模

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The molecular mechanism of blue color formation in an iodine-starch reaction is studied by employing the iodine-alpha-cyclodextrin (alpha-CD) complex as a practical model system that resembles the structural properties of the blue amylose-iodine complex, To this end, we construct, using the quantum chemistry method, a molecular model of the complex (I-5(-)/Li+/2 alpha-CD) that consists of one I-5(-), two molecules of alpha-CD, and a lithium cation, and this model is employed as a basic unit in constructing the structural models of polyiodide ions (I-5(-))(n). The initial structure in the geometry optimization is adopted from the alpha-CD-iodine complex structure obtained from the X-ray crystallography study. The structural models of (I-5(-))(n) are built by adding the basic unit n times along the crystal axis and by optimizing the structure using quantum mechanics/molecular mechanics (QM (iodine)/MM (alpha-CD)) calculations. The electronic absorption spectra of the resulting model structures are calculated by time-dependent density functional theory (TD-DFT). We find that I-5(-) acts as a basic unit of coloration in the visible region. The visible color originates from the electronic transition within the I-5(-) molecule, and any charge transfer between the I-5(-) ion and either of alpha-CD or a coexisting counter cation is not involved. We also reveal that the electronic transitions of (I-5(-))(n) are delocalized, which accounts for the well-known observation that the color of the iodine-starch reaction becomes bluish with an increase in the chain length of amylose. Furthermore, the preresonance Raman spectra calculated from the model suggest that the vibrational motions are localized in the I-5(-) subunit dominantly. A comparison between an experimental absorption spectrum feature of the alpha-CD-iodine complex and the calculated ones of (I-5(-))(n) ions with various n values suggests that (I-5(-))(4) polyiodide ions tend to be populated dominantly in the alpha-CD-iodine complex under aqueous conditions.
机译：通过采用碘-α-环糊精（α-CD）复​​合物作为类似模型系统的碘 - α-环糊精（α-CD）复​​合物来研究蓝色形成在碘 - 淀粉反应中的分子机制。 ，我们用量子化学方法构建复合物的分子模型（I-5（ - ）/ Li + / 2α-CD），该模型由一个I-5（ - ），两种分子的α-CD和阳离子，并且该模型用于构建聚碘离子结构模型（I-5（ - ））（n）的基本单元。从X射线晶体学研究获得的α-CD-碘复合结构中采用几何优化中的初始结构。 （I-5（ - ））（n）的结构模型是通过沿着晶体轴的基本单元n次构成的构建，并通过使用量子力学/分子力学（QM（碘）/ mm（α-CD ））计算。通过时间依赖的密度泛函理论（TD-DFT）计算所得模型结构的电子吸收光谱。我们发现I-5（ - ）作为可见区域中的着色单位。可见光源自I-5（ - ）分子内的电子转换，并且不涉及I-5（ - ）离子和α-CD中的任何一种电荷转移或α-CD或共存反应阳离子。我们还揭示了（I-5（ - ））（n）的电子转换是划分的，其占众所周知的观察，即碘 - 淀粉反应的颜色随着链烷糖的链长而变得蓝色。此外，由模型计算的预谐振谱表明，振动运动在I-5（ - ）亚基中占据了主要的。 α-CD-碘复合物的实验吸收光谱特征与具有各种n值的（I-5（ - ））（N）离子的计算的实验吸收光谱特征的比较表明（I-5（ - ））（4）在水性条件下，聚碘碘化物离子倾向于在α-CD-碘配合物中占群体。

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