Antioxidant Activity of Natural Antioxidants versus Reactive Oxygen Species in Emulsion Systems and Its Spin-Dynamics

本研究采用基于荧光或ESR检测的时间分辨方法，对天然抗氧化剂维生素E和儿茶素在乳状液相中的抗氧化反应与氧自由基的关系进行了动力学研究。1.首次用荧光检测停流法得到了模型自由基在VE乳状液体系中清除反应的二级速率常数。结果表明，乳状液体系的速率常数与均相溶液中的不同。这种动力学方法也适用于乳液体系中其他自由基的清除反应。2.为了研究乳液体系中单线态氧(^1O2)的动力学，用时间分辨近红外荧光光谱仪直接测量了^1O2在1275 nm处的发射。在VE乳状液体系中，随着VE浓度的增加，^1O_2的寿命延长，而在均相溶液中，VE的猝灭速率常数通常表现为10.7~10^8M^&lt；-1；S。3利用时间分辨ESR和瞬时吸收法研究了天然维生素E和过氧化氢激光激发产生的短寿命中间自由基的自旋动力学，为研究生物体系、胶体、食品和饮料等生物体系乳化相中自由基和^1O2的动力学和自旋动力学提供了时间分辨工具。所获得的乳状液体系的信息将阐明非均相体系中的独特动力学。

In the present study, a kinetic investigation was progressed on the antioxidant reactions versus reactive oxygen species for natural antioxidants, such as vitamin E and catechins, in the emulsion phase by using time-resolved methods based on the fluorescence or ESR detection.1.The second-order rate constant for the scavenging reaction of the model free-radical in vitamin E (VE) emulsion systems was firstly obtained by using the fluorescence-detected stopped-flow method. The result indicates that the rate constants in emulsion systems are different from that in the homogeneous solution. This kinetic approach could also be applicable to the scavenging reaction of other radicals, such as galvinoxyl and DPPH, in emulsion systems.2.For investigating the dynamics of singlet oxygen (^1O_2) in the emulsion systems, the emission (at 1275 nm) from ^1O_2 was measured directly by using a time-resolved near-infrared fluorescence spectrophotometer. In the VE emulsion system, the life-time of ^1O_2 increases with an increase of the concentration of VE, while the VE usually shows 10^7 - 10^8 M^<-1>s^<-1> as the ^1O_2 quenching rate constant in homogeneous solutions. The result suggests that the ^1O_2 dynamics occurs mainly near the oil-droplet of VE in this system.3 The investigation on the spin-dynamics for the short-lived intermediate radials generated by the laser excitation of natural vitamin E and hydroperoxide is progressed by using the time-resolved ESR and transient absorption methods.The results of the present study give the time-resolved tools for investigating the kinetics and the spin-dynamics of the free-radicals and ^1O_2 in emulsion phase, which is a model of biological systems, colloids, food, and drinks. The obtained information for emulsion systems will clarify the unique dynamics in inhomogeneous systems.