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A Photoprotective Effect by Cation‐π‐Interaction? Quenching of Singlet Oxygen by an Indole‐Cation‐π Model System
Photochemistry and Photobiology ( IF 2.6 ) Pub Date : 2020-06-20 , DOI: 10.1111/php.13287
Gary E Arevalo 1 , David A Cagan 1 , Charlotte G Monsour 1 , Arman C Garcia 1 , Alison McCurdy 1 , Matthias Selke 1
Affiliation  

We investigated the effect of the cation‐π interaction on the susceptibility of a tryptophan model system toward interaction with singlet oxygen, that is, type II photooxidation. The model system consists of two indole units linked to a lariat crown ether to measure the total rate of removal of singlet oxygen by the indole units in the presence of sodium cations (i.e. indole units subject to a cation‐π interaction) and in the absence of this interaction. We found that the cation‐π interaction significantly decreases the total rate of removal of singlet oxygen (kT) for the model system, that is, (kT = 2.4 ± 0.2) × 108 m−1 s−1 without sodium cation vs (kT = 6.9 ± 0.9) × 107 m−1 s−1 upon complexation of sodium cation to the crown ether. Furthermore, we found that the indole moieties undergo type I photooxidation processes with triplet excited methylene blue; this effect is also inhibited by the cation‐π interaction. The chemical rate of reaction of the indole groups with singlet oxygen is also slower upon complexation of sodium cation in our model system, although we were unable to obtain an exact ratio due to differences of the chemical reaction rates of the two indole moieties.

中文翻译:

阳离子-π-相互作用的光保护作用?通过吲哚-阳离子-π模型系统淬灭单线态氧

我们研究了阳离子-π 相互作用对色氨酸模型系统对与单线态氧相互作用的敏感性的影响,即 II 型光氧化。该模型系统由两个与套索冠醚相连的吲哚单元组成,用于测量在钠阳离子(即受阳离子-π 相互作用的吲哚单元)存在和不存在的情况下吲哚单元去除单线态氧的总速率这种互动。我们发现阳离子-π 相互作用显着降低了模型系统的单线态氧 (kT) 去除总速率,即 (kT = 2.4 ± 0.2) × 108 m−1 s−1 无钠阳离子 vs (kT = 6.9 ± 0.9) × 107 m−1 s−1 钠阳离子与冠醚络合后。此外,我们发现吲哚部分在三重激发的亚甲基蓝下经历了 I 型光氧化过程;这种效应也受到阳离子-π相互作用的抑制。在我们的模型系统中,吲哚基团与单线态氧的化学反应速率在钠阳离子络合时也较慢,尽管由于两个吲哚部分的化学反应速率不同,我们无法获得准确的比率。
更新日期:2020-06-20
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