咖啡酸及其衍生物光谱特性研究

研究了不同pH值条件下 ,咖啡酸类化合物溶液的荧光及紫外光谱特性。实验结果表明 :咖啡酸类化合物有很宽的pH发光范围 (2～ 1 2 ) ,发光强度、光谱形状及峰位随pH值不同而异 ,且在pH =9～ 1 0时 ,咖啡酸类化合物荧光强度最强。研究还发现 :咖啡酸类化合物 4 位酚羟基的解离可导致荧光强度显著增强 ,而 3 位酚羟基的解离可能会导致荧光猝灭 ,并且在强酸和强碱介质中发射荧光均被显著猝灭 ;此外 ,在强碱性介质中紫外光谱形状有很大变化 ,表明咖啡酸类化合物在强碱性下分子结构发生了明显改变。

Study on the Spectral Properties of Caffeic Acid and Its Derivatives

Caffeic acid, chlorogenic acid and forsythiaside are active components of Chinese herbs and have diverse biological activities. As the similar compounds, they all include 3, 4-dihydroxy-phenyl in their structures. In this paper, the fluorescence and UV spectra of the caffeic acid, chlorogenic acid and forsythiaside were studied in different pH. The spectra properties of fluorescence and UV were further discussed in view of the phenol hydroxyl states, free, dissociative and protonated. It is found that the luminescence intensity, the peak shape and peak wavelength change with pH. Experimental results also indicate that caffeic acid, chlorogenic acid and forsythiaside can emit fluorescence in wide range of pH (2-12), and fluorescent intensity is enhanced as the dissociation of 4-phenol hydroxyl. On the other hand, fluorescent intensity may be quenched as the dissociation of 3-phenol hydroxyl. Furthermore, in strong acidic or in strong basic media, the fluorescence is quenched partly, and the shape of UV spectra changed greatly in strong basic media, meaning that their molecular structures are changed considerable.