Neunert Grazyna, Szwengiel Artur, Walejko Piotr, Witkowski Stanislaw, Polewski Krzysztof
Department of Physics and Biophysics, Poznan University of Life Sciences, ul. Wojska Polskiego 38/42, 60-637 Poznan, Poland.
Institute of Food Technology, Poznan University of Life Sciences, ul. Wojska Polskiego 38/42, 60-637 Poznan, Poland.
J Photochem Photobiol B. 2016 Jul;160:121-7. doi: 10.1016/j.jphotobiol.2016.03.032. Epub 2016 Apr 2.
α-Tocopherol (Toc) is known to degrade to the tocopheroxyl radicals (Toc) by exposure to UV light irradiation. In the present study, the stability of Toc ester derivatives exposed to UV light was investigated and compared with Toc in organic solution and in phospholipid vesicles. To follow the depletion of Toc and its esters the absorbance and fluorescence methods were applied whereas degradation products were detected using LC-MS method. The irradiation with UVB light of air-equilibrated solutions of di-α-Tocopheryl malonate (DTMO), α-Tocopheryl malonate (TMO) and α-Tocopheryl succinate (TS) strongly modifies their absorption and fluorescence spectra. Upon UVB irradiation, absorption band at 279/285nm becomes less pronounced indicating the photodegradation of esters. During irradiation, the fluorescence maximum of esters at 305nm shifts to 326nm, a maximum characteristic for Toc. Photorecovery of Toc from its esters derivatives was finally confirmed by LC-MS method. Among studied esters, only α-tocopheryl nicotinate (TN) did not undergo depletion and appeared resistant to UVB radiation. Kinetic studies indicated that photoinduced transformation occurs through the first order consecutive reaction chain mechanism. The photodissociation of Toc esters in the liposomes occurred with one order of magnitude slower than in organic solvents. Using MS/MS method it was found that final stable product of irradiation was α-tocopheryl quinone (TQ), an animal and plant metabolite of Toc.
已知α-生育酚（Toc）通过暴露于紫外线照射会降解为生育酚氧基自由基（Toc）。在本研究中，研究了Toc酯衍生物在紫外线照射下的稳定性，并与有机溶液和磷脂囊泡中的Toc进行了比较。为了跟踪Toc及其酯的消耗情况，采用了吸光度和荧光方法，而降解产物则使用液相色谱-质谱法进行检测。用中波紫外线照射二-α-生育酚丙二酸酯（DTMO）、α-生育酚丙二酸酯（TMO）和α-生育酚琥珀酸酯（TS）的空气平衡溶液，会强烈改变它们的吸收光谱和荧光光谱。在中波紫外线照射下，279/285nm处的吸收带变得不那么明显，表明酯发生了光降解。在照射过程中，酯在305nm处的荧光最大值移至326nm，这是Toc的特征最大值。最终通过液相色谱-质谱法证实了Toc从其酯衍生物中的光恢复。在所研究的酯中，只有α-生育酚烟酸酯（TN）没有消耗，并且对中波紫外线辐射具有抗性。动力学研究表明，光诱导转化通过一级连续反应链机制发生。脂质体中Toc酯的光解离比在有机溶剂中慢一个数量级。使用串联质谱法发现，照射的最终稳定产物是α-生育酚醌（TQ），它是Toc的动植物代谢产物。
