基于拉曼光谱和三维荧光光谱的三角帆蚌淡水珍珠及其蚌壳的色素研究

Study on Pigments in Freshwater Pearls and Hyriopsis Cumingii Based on Raman Spectra and EEM Spectra

  • 摘要: 颜色是评价珍珠质量的重要因素,但其致色物质仍未有定论。在珍珠生长过程中,颜色可能受到母蚌影响。为研究二者的关联,本研究以三角帆蚌及其培育的无核珍珠样品为研究对象,使用拉曼光谱与三维荧光光谱对其进行检测分析,并运用量子化学计算色素结构的理论拉曼光谱。结果发现,不同颜色珍珠样品中多烯色素的拉曼光谱特征基本相似,都具有C=C双键伸缩振动峰与C-C单键伸缩振动峰;区别在于不同颜色珍珠的具体拉曼峰位,这是由于多烯色素的共轭链长不同导致。橙黄色珍珠与紫色珍珠样品中的多烯色素分别含有10个C=C双键和12个C=C双键;珍珠样品的颜色越深,三维荧光光谱的强度越弱, 荧光中心位置均位于284 nm/340 nm处。淡水珍珠与三角帆蚌蚌壳的拉曼光谱与三维荧光光谱特征几乎相同,说明二者成分高度相似,推测二者在生物矿化过程中色素的分泌与代谢过程非常相似。

     

    Abstract: Colour is an important factor in evaluating the quality of pearl and directly affects its value. But definitive conclusion about the pigments of pearls has not yet been determined. During the growth process, the colour of pearl may be affected by its mussel. In order to study the relationship between pigments in pearls and mussels, Hyriopsis cumingii and its non-nucleated pearls were selected and their Raman spectra and excitation-emission matrix (EEM) spectra were collected. The theoretical Raman spectra of possible pigment structures were calculated by quantum chemistry. The results show that the Raman spectral characteristics of pearls of different colours are similar but also different. The similarity is that they all present the characteristics of polyene pigments: they all have the stretching vibration of C=C double bond and the stretching vibration of C-C single bond. While the Raman peak positions of pearls with different colour perform different. This is due to the different conjugated chain lengths of polyene pigments. The polyene pigments in orange yellow pearls and purple pearls contain 10 C=C double bonds and 12 C=C double bonds, respectively. In terms of EEM spectral characteristics, the darker the pearl colour, the weaker the fluorescence intensity. The fluorescence centers are located at 284 nm/340 nm. The Raman spectra and EEM spectra of freshwater pearls and Hyriopsis cumingii shells are almost identical, indicating a high degree of similarity in their composition. It is speculated that the secretion and metabolism of pigments in the biomineralization process of the two are very similar.

     

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