Liu Zhen, Xue Ling, Jia Yuan, Lou Boyu, Yang Juxiang
School of Chemical Engineering, Xi'an University No. 1 Keji 6th Road Xi'an Shaanxi 710065 China
RSC Adv. 2019 Apr 11;9(20):11281-11288. doi: 10.1039/c8ra10153a. eCollection 2019 Apr 9.
In this article, both experimental and computational methods are employed to investigate the photophysics of rhaponticin (RH). The bathochromic shift was observed in absorption and fluorescence spectra with increasing solvent polarity, which implied that the charge transition of RH involved was π → π*. The results showed that RH possess strong intramolecular charge transfer (ICT), and the most important parameter to characterize the photophysical behavior of RH is the intermolecular hydrogen bonding ability of the solvent. The hydrogen bonding effect occurred at the localized electron-acceptor oxygen at the glycoside bond. Density functional theory (DFT) and time dependent density functional theory (TDDFT) were used to obtain the most stable structure, electronic excitation energy, dipole moments and charge distribution. The result was found to be 2.23 and 3.67 D in ground state and excited state respectively. Fluorescence quenching of RH owing to the photoinduced electron transfer (PET) is facilitated in alkaline media. The p value of RH was 6.39, which defined RH as a highly efficient "off-on" switcher. The effect of different metal ions on the fluorescence spectra of RH was also investigated, and the fluorescence quenching of RH depended on the nature of ions. The best performance was accomplished for binding with the Fe ion. The interactions of RH with the Fe ion were studied by FT-IR and HPLC, and the binding parameter was calculated by the Stern-Volmer equation. The results obtained reveal the binding activity of RH can make this a candidate as a good source of new agents for thalassemic patients.
在本文中，采用实验和计算方法研究了土大黄苷（RH）的光物理性质。随着溶剂极性增加，在吸收光谱和荧光光谱中观察到红移，这表明RH涉及的电荷跃迁为π→π*。结果表明，RH具有较强的分子内电荷转移（ICT），表征RH光物理行为的最重要参数是溶剂的分子间氢键能力。氢键效应发生在糖苷键处的局域电子受体氧上。采用密度泛函理论（DFT）和含时密度泛函理论（TDDFT）获得最稳定结构、电子激发能、偶极矩和电荷分布。结果发现基态和激发态的偶极矩分别为2.23 D和3.67 D。在碱性介质中，由于光致电子转移（PET）促进了RH的荧光猝灭。RH的pKa值为6.39，这将RH定义为一种高效的“关-开”切换剂。还研究了不同金属离子对RH荧光光谱的影响，RH的荧光猝灭取决于离子的性质。与铁离子结合表现出最佳性能。通过傅里叶变换红外光谱（FT-IR）和高效液相色谱（HPLC）研究了RH与铁离子的相互作用，并通过Stern-Volmer方程计算了结合参数。所得结果表明，RH的结合活性使其有望成为地中海贫血患者新型药物的良好来源。
