DeHaven Baillie A, Liberatore Hannah K, Greer Alexander, Richardson Susan D, Shimizu Linda S
Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, United States.
Department of Chemistry, Brooklyn College, Brooklyn, New York 11210, United States.
ACS Omega. 2019 May 8;4(5):8290-8298. doi: 10.1021/acsomega.9b00831. eCollection 2019 May 31.
Herein, we examine the photochemical formation of reactive oxygen species (ROS) by a porous benzophenone-containing bis-urea host () to investigate the mechanism of photooxidations that occur within the confines of its nanochannels. UV irradiation of the self-assembled host in the presence of molecular oxygen generates both singlet oxygen and superoxide when suspended in solution. The efficiency of ROS generation by the host is lower than that of benzophenone (BP), which could be beneficial for reactions carried out catalytically, as ROS species react quickly and often unselectively. Superoxide formation was detected through reaction with 5,5-dimethyl-1-pyrroline -oxide in the presence of methanol. However, it is not detected in CHCl, as it reacts rapidly with the solvent to generate methaneperoxy and chloride anions, similar to BP. The lifetime of airborne singlet oxygen (τ) was examined at the air-solid outer surface of the host and host·quencher complexes and suggests that quenching is a surface phenomenon. The efficiency of the host and BP as catalysts was compared for the photooxidation of 1-methyl-1-cyclohexene in solution. Both the host and BP mediate the photooxidation in CHCl, benzene, and benzene- , producing primarily epoxide-derived products with low selectivity likely by both type I and type II photooxidation processes. Interestingly, in CHCl, two chlorohydrins were also formed, reflecting the formation of chloride in this solvent. In contrast, UV irradiation of the host·guest crystals in an oxygen atmosphere produced no epoxide and appeared to favor mainly the type II processes. Photolysis afforded high conversion to only three products: an enone, a tertiary allylic alcohol, and a diol, which demonstrates the accessibility of the encapsulated reactants to oxygen and the influence of confinement on the reaction pathway.
在此，我们研究了含二苯甲酮的多孔双脲主体（）光化学生成活性氧（ROS）的过程，以探究在其纳米通道范围内发生的光氧化反应机制。当自组装主体在分子氧存在下进行紫外线照射时，悬浮于溶液中会同时生成单线态氧和超氧阴离子。主体生成ROS的效率低于二苯甲酮（BP），这对于催化反应可能是有益的，因为ROS种类反应迅速且往往具有非选择性。超氧阴离子的生成是通过在甲醇存在下与5,5 - 二甲基 - 1 - 吡咯啉 - N - 氧化物反应检测到的。然而，在CHCl₃中未检测到超氧阴离子，因为它会与溶剂迅速反应生成甲烷过氧自由基和氯离子，这与BP类似。在主体和气 - 固外表面以及主体·猝灭剂复合物处对空气中单线态氧的寿命（τ）进行了研究，结果表明猝灭是一种表面现象。比较了主体和BP作为催化剂对溶液中1 - 甲基 - 1 - 环己烯光氧化反应的催化效率。主体和BP在CHCl₃、苯和苯 - d₆中均介导光氧化反应，主要通过I型和II型光氧化过程生成选择性较低的环氧化物衍生产物。有趣的是，在CHCl₃中还形成了两种氯代醇，这反映了该溶剂中氯离子的生成。相比之下，在氧气气氛中对主体 - 客体晶体进行紫外线照射未产生环氧化物，且似乎主要有利于II型过程。光解仅能高效转化为三种产物：一种烯酮、一种叔烯丙醇和一种二醇，这表明被包封的反应物能够接触到氧气，以及受限环境对反应途径的影响。
