天然染料苏木的光褪色机理研究

Towards the photodegradation mechanism of sappanwood dye

有机质文物如书画和纺织品在修复保护过程中常常遇到褪色问题,对于染料分子是一种不可逆的损伤,因此有必要采用一定的科学方法对原因机理进行研究。苏木在文化遗产领域常作为天然染料用于纺织品染色,但色牢度较差。通过溶液动力学模拟实验借助紫外光老化过程推测降解副产物,追踪了对曾经在文物中检测到的有效化学组分巴西苏木素和原苏木素B在N,N-二甲基甲酰胺基质里光催化老化代谢过程,分别获得20组不同老化程度的紫外老化的标准品。实验表征手段主要采用紫外可见漫反射光谱、超高效液相色谱四极杆飞行时间质谱联用及核磁共振氢谱对颜色变化趋势和老化过程进行分析。通过苏木染色及丝织品光老化实验,得到17组不同褪色程度的纺织品样品。采用液质联用在负离子模式下结合化学计量学统计分析差异代谢物及老化机制,巴西苏木素、苏木红素及原苏木素B可能的转化及降解产物分别得到一定的推论。结果显示褪色纺织品随着光老化的发生反射光谱最大波长总体发生蓝移。巴西苏木素季碳羟基容易发生脱水反应产生一系列变化,原苏木素B光老化过程容易转化成原苏木素C、尿石素C等化合物。苏木染褪色纺织品总体可分为两类组间差异,通过主成分分析出差异代谢物巴西苏木素、原苏木素B以及C等多种老化产物,这些总体因素造成体系的光老化颜色变化。这些探索性发现期待为今后天然染料的相关研究提供启发,助力提升有机质文物的科学价值认知。

For organic cultural relics such as paintings and textiles,a very typical fading problem is often discovered during their conservation and restoration.It is necessary to conduct mechanism research using scientific methodology since this is an irreversible change for dye molecules.Caesalpinia sappan L.,known as sappanwood or brazilwood,is famous,worldwide,as a natural red dye,but it is very poor in light fastness.The aim of this research was to investigate the fading using accelerated photodegradation and speculate the photofading by-products in the form of simulated UV ageing experiments.The solution kinetics of brazilin and protosappanin B,which have been found in relics,were studied in solvent DMF,and 20 sets of UV accelerated ageing standards were obtained.The products were analyzed using UV-Vis diffuse reflection spectrometry,ultra-high-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry(UPLC-QTOF MS)and proton nuclear magnetic resonance spectrometry(1H NMR).These tools were applied together to analyze the color change trends and ageing process.17 different photodegradation silk samples dyed with sappanwood were analyzed using UPLC-QTOF MS in the negative ion mode in combination with chemometrics.The results show that the fading produced a hypsochromic shift of max peak positions in their reflectance spectra with light ageing.The hydroxyl group of quaternary carbon in brazilin tended to dehydrate and made a series of changes while protosappanin B was easily converted into several compounds such as protosappanin C and urolithin C during the photoageing process.The simulated fading textiles dyed with sappanwood could be generally divided into two differential groups and differential metabolites including brazilin,protosappanin B and C could be analyzed through principal component analysis.These overall factors eventually caused the color change.These results are expected to be helpful to the research on natural dyes in textile heritages.