Department of Environmental and Chemical Engineering, Hebei College of Industry and Technology, Shijiazhuang 050091, China.
College of Chemistry and Material Science, Hebei Normal University, Shijiazhuang 050024, China.
Molecules. 2023 Feb 5;28(4):1543. doi: 10.3390/molecules28041543.
In this work, the origins for the spectral difference between two isoflavones, formononetin (F) and ononin (FG), are revealed via a comparison study of the fluorescence molecular structure. The fluorescence enhancement of FG in hot alkaline conditions is reported for the first time. For F, there is almost no fluorescence under acidic conditions, but when the pH is >4.8, its fluorescence begins to increase due to the deprotonation of 7-OH. Under a pH between 9.3 and 12.0, the anionic form of F produces a strong and stable fluorescence. The fluorescence quantum yield (Yf) of F is measured to be 0.042. FG shows only weak fluorescence in aqueous solutions under a wide range of pH until it is placed in hot alkaline solutions, which is attributed to the cleavage reaction of the γ-pyrone ring in FG. The Yf of FG is determined to be 0.020. Based on the fluorescence sensitization methods of F and FG, the quantitative analysis and detection of two substances can be realized. The limit of the detections for F and FG are 2.60 ng·mL and 9.30 ng·mL, respectively. The linear detection ranges of F and FG are 11.71860 ng·mL and 14.62920 ng·mL, respectively. Although the structural relationship between F and FG is glycoside and aglycone, under hot alkaline conditions, the final products after the cleavage and hydrolysis reactions are essentially different. The different fluorescence characteristics between F and FG pave a way for further identification and a quantitative analysis of the corresponding components in Chinese herbal medicine.
在这项工作中，通过对荧光分子结构的比较研究，揭示了两种异黄酮——芒柄花素（F）和大豆苷元（FG）之间光谱差异的起源。首次报道了 FG 在热碱性条件下的荧光增强现象。对于 F，在酸性条件下几乎没有荧光，但当 pH 值大于 4.8 时，由于 7-OH 的去质子化，其荧光开始增加。在 pH 值在 9.3 到 12.0 之间时，F 的阴离子形式产生强而稳定的荧光。测得 F 的荧光量子产率（Yf）为 0.042。FG 在很宽的 pH 范围内的水溶液中仅显示出微弱的荧光，直到将其置于热碱性溶液中，这归因于 FG 中γ-吡喃酮环的裂解反应。FG 的 Yf 被确定为 0.020。基于 F 和 FG 的荧光敏化方法，可以实现两种物质的定量分析和检测。F 和 FG 的检测限分别为 2.60 ng·mL 和 9.30 ng·mL。F 和 FG 的线性检测范围分别为 11.71860 ng·mL 和 14.62920 ng·mL。尽管 F 和 FG 的结构关系是糖苷和苷元，但在热碱性条件下，裂解和水解反应的最终产物本质上是不同的。F 和 FG 之间不同的荧光特性为进一步鉴定和定量分析中草药中的相应成分铺平了道路。
