摘要
红曲色素在自然光的作用下会逐渐褪色,紫外线是自然光中引起有机物褪色的主要光线。为了探明红曲色素光照褪色的机理,采用紫外灯照射一种红曲红色素(分子式C19H28N2O5)的水溶液至无色,经红外光谱、质谱和核磁图谱分析,鉴定其褪色后物质的分子式为C14H9NO6。根据光化学理论分析,提出了红曲红色素的光褪色机理:在紫外光作用下,红曲红色素分子中的脂肪族侧链首先在α-碳原子处发生NorrishⅠ型断裂,成为自由基,随后在碳7位甲基上发生相同反应,接着色素发生电子转移,双键转换,水溶液中产生羟自由基、超氧阴离子等自由基,与色素结构中双键发生加成反应,共轭双键消失,色素失去颜色。防止红曲红色素光褪色应首先考虑稳定其脂肪族侧链结构,其次可以在色素中添加自由基清除剂。
Monascus pigment fades in sun light, and ultraviolet radiation （UV） is main reason causing photobleaching of organic compound. To study the mechanism of photobleaching for monascus pigments, a monascus red pigment （resolved in water, molecular formula C19H28 N2O5 ） is radiated with UV-light until colorless, the molecular formula of the colorlessness is determined as C14H9NO6 by infrared spectrometry, mass spectrometry and hydrogen nuclear magnetic resonance. The photobleaching mechanism of the red pigment is deduced according to photochemical theory： firstly, the acyclic side-chain in monascus pigment is cut at a-carbon according to Norrish I mode, radicals are formed, and then same reaction happens at 7-carbon methyl; electron-transferring, double-bond conversion and addition reaction between double-bond and hydroxyl radical, superoxide radical from water occurrs, and conjugated double-bond disappeares, which causes bleaching of monascus pigments. In order to avoid bleaching of monascus pigments, stabilization of acyclic side-chain should be considered primarily, and addition of radical clearing reagents in pigments is also prefered.
出处
《光学学报》
EI
CAS
CSCD
北大核心
2006年第8期1256-1259,共4页
Acta Optica Sinica
基金
国家自然科学基金(20576100)资助课题
关键词
光谱学
光褪色
喷雾质谱
W-红色素
spectroscopy
photobleaching
electro-spray ionization-mass spectrometry
W-red pigment
