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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Watching the conformational changes of maleonitriledithiolate chromophores inside the inclusion complexes with cyclodextrins: Probed by ICD spectra and DFT calculations
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Watching the conformational changes of maleonitriledithiolate chromophores inside the inclusion complexes with cyclodextrins: Probed by ICD spectra and DFT calculations

机译：观察含有环糊精的包合物中马来腈基硫氰酸盐发色团的构象变化：通过ICD光谱和DFT计算探究

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摘要

A series of inclusion complexes between cyclodextrins (α-, β-, γ-cyclodextrin and HP-β-cyclodextrin, HP-β-cyclodextrin = 2-hydroxypropyl-β-cyclodextrin) and sodium maleonitriledithiolate (Na _2mnt) were investigated by electronic spectra, induced circular dichroism (ICD) spectra, and quantum chemical studies. The inclusion complexes Na_2mntα-cyclodextrin and Na_2mntγ-cyclodextrin did not show any ICD signals, whereas Na_2mnt@HP-β-cyclodextrin displayed two signs of splitting Cotton effects (CEs), with one positive CE couplet at 376 nm in the 365-410 nm region and the other negative at 277 nm in the 265-306 nm region. In addition, a dimeric host inclusion pattern of Na _2mnt@HP-β-cyclodextrin in solution was determined by the method of continuous variation. Density functional theory (DFT) was used to assist assignment of the ICD signals in inclusion complexes Na_2mntβ- cyclodextrin and Na_2mnt@HP-β-cyclodextrin in combination with the well-known Harata's rule. The orientation of p → π* transition in Na_2mnt chromophore was predicted by TD-DFT (time-dependent DFT) calculations to be along the C - C double bond instead of being perpendicular. Upon titrations with Zn~(2+) solutions, reversals of the p → π* transition-relevant ICD peak and splitting CE were experimentally observed in the cases of Na_2mntβ-cyclodextrin and Na _2mnt@HP-β-cyclodextrin, respectively, which strongly supported our hypotheses on their coconformations and the subsequent conformational changes of mnt chromophores occurring during the titration procedures. Therefore, on the basis of both the experimental data and TD-DFT calculations, the HP-β-cyclodextrin dimer host in inclusion complex Na _2mnt@HP-β-cyclodextrin was disclosed, which in turn generated the exciton coupling between the two individually included guests and produced the splitting CEs as well as the reversals of CEs.
机译：通过电子光谱研究了环糊精（α-，β-，γ-环糊精和HP-β-环糊精，HP-β-环糊精= 2-羟丙基-β-环糊精）和顺丁烯二腈二硫代硫酸钠（Na _2mnt）之间的一系列包合物。 ，诱导圆二色性（ICD）光谱和量子化学研究。包合物Na_2mntα-环糊精和Na_2mntγ-环糊精未显示任何ICD信号，而Na_2mnt @HP-β-环糊精显示出两个分裂棉效应的迹象（CEs），在365-410 nm处的376 nm处有一个正CE对联。 265-306 nm区域中的另一个负值位于277 nm。另外，采用连续变异法确定了溶液中Na _2mnt @HP-β-环糊精的二聚体宿主包涵体模式。结合泛函法则，使用密度泛函理论（DFT）协助对内含物Na_2mntβ-环糊精和Na_2mnt @HP-β-环糊精中的ICD信号进行分配。通过TD-DFT（随时间变化的DFT）计算可预测Na_2mnt发色团中p→π*跃迁的方向沿CC双键而不是垂直。在用Zn〜（2+）溶液滴定后，分别在Na_2mntβ-环糊精和Na _2mnt @HP-β-环糊精中分别观察到p→π*跃迁相关的ICD峰和裂解CE的反转。支持我们关于它们的共构象以及滴定过程中发生的mnt发色团构象变化的假设。因此，基于实验数据和TD-DFT计算，揭示了包合物Na _2mnt @HP-β-环糊精中的HP-β-环糊精二聚体，进而在两个包合物中产生了激子耦合。来宾并产生了分裂的CE以及CE的反转。

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