Laser flash photolysis study on the retinol radical cation in polar solvents
Laser flash photolysis study on the retinol radical cation in polar solvents
复制标题
DOI：
10.1039/c1ob05814b
复制
发表时间：
2011-01-01
影响因子：
3.2
通讯作者：
Fukuzumi, Shunichi
中科院分区：
文献类型：
--
作者：
El-Agamey, Ali;Fukuzumi, Shunichi
视黄醇在氩饱和甲醇中的激光闪光光解（LFP）在580 nm处产生瞬态（瞬态A）。瞬态A的形成伴随着在370 nm处的瞬态生长。这种生长速率是视黄醇浓度依赖性的。在370 nm处的瞬态生长在N2 O的存在下被去除，N2 O已知会抑制溶剂化电子。这些结果可以通过视黄醇（中心点+）（λ（max）= 580 nm）的形成和视黄醇的LFP之后的溶剂化电子来解释。随后，溶剂化的电子被视黄醇快速清除，形成视黄醇中心点（λ（max）= 370 nm，在甲醇中）。另一方面，瞬态A不归因于视黄基阳离子，如先前所提出的，因为视黄基阳离子（由视黄基乙酸酯的LFP产生）和瞬态A对卤离子显示出不同的反应性（例如，在乙腈中，k（Br）分别为1.7 x 10（9）和1.51 x 10（10）M-1 s（-1））。在证明了瞬时A作为视黄醇中心点（+）的身份后，在空气饱和的极性溶剂中检测了其与类胡萝卜素的反应。在类胡萝卜素的存在下，观察到视黄醇（中心点+）的衰变增强，并伴随着通过电子转移从类胡萝卜素到视黄醇（中心点+）形成相应的类胡萝卜素自由基阳离子。此外，视黄醇（中心点+）对吡啶衍生物的反应性进行了研究，在空气饱和的极性溶剂。结果发现，视黄醇（中心点+）的衰减加速，伴随着在370 nm处以相同速率形成瞬态。随着视黄醇的空气饱和的2%Triton X-100水溶液（中心点+）的pH增加，获得了类似的观察结果。370 nm（或380 nm的Triton X-100的情况下）瞬态归因于碱加合物或去质子化的中性自由基。在这些结果的基础上，视黄基阳离子和视黄醇（中心点+）的反应性进行了比较和视黄醇（中心点+）的生物环境内形成的后果进行了讨论。
Laser flash photolysis (LFP) of retinol in argon-saturated methanol gives rise to a transient at 580 nm (transient A). Formation of transient A is accompanied by a transient growth at 370 nm. The rate of this growth is retinol concentration-dependent. The transient growth at 370 nm was removed in the presence of N2O, which is known to scavenge solvated electrons. These results can be interpreted by formation of retinol(center dot+) (lambda(max) = 580 nm) and solvated electrons following LFP of retinol. Subsequently, the solvated electrons are rapidly scavenged by retinol to form retinol center dot (lambda(max) = 370 nm in methanol). On the other hand, transient A is not ascribed to the retinyl cation, as was previously proposed, because the retinyl cation, generated from LFP of retinyl acetate, and transient A show different reactivities towards halide ions (e.g. k(Br) = 1.7 x 10(9) and 1.51 x 10(10) M-1 s(-1) respectively, in acetonitrile). After demonstrating the identity of transient A as retinol center dot(+), its reactions with carotenoids were examined in air-saturated polar solvents. In the presence of carotenoids, an enhancement in the decay of retinol(center dot+) was observed and was accompanied by formation of the corresponding carotenoid radical cations via electron transfer from carotenoids to retinol(center dot+). Furthermore, the reactivity of retinol(center dot+) towards pyridine derivatives was investigated in air-saturated polar solvents. It was found that the decay of retinol(center dot+) was accelerated with concomitant formation, with the same rate, of a transient at 370 nm. Similar observations were obtained with increasing pH of air-saturated aqueous 2% Triton X-100 of retinol(center dot+). The 370 nm (or 380 nm in the case of Triton X-100) transient is attributed to the base adducts or deprotonated neutral radicals. On the basis of these results, the reactivities of the retinyl cation and retinol(center dot+) are compared and the consequences of retinol(center dot+) formation within biological environments are discussed.