Ding Bo-Wen, Naumov Panče, Liu Ya-Jun
Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry, Beijing Normal University , Beijing 100875, China.
New York University Abu Dhabi , P.O. Box 129188, Abu Dhabi, United Arab Emirates.
J Chem Theory Comput. 2015 Feb 10;11(2):591-9. doi: 10.1021/ct5009203.
Cypridina hilgendorfii (sea firefly) is a bioluminescent crustacean whose bioluminescence (BL) reaction is archetypal for a number of marine organisms, notably other bioluminescent crustaceans and coelenterates. Unraveling the mechanism of its BL is paramount for future applications of its strongly emissive lumophore. Cypridina produces light in a three-step reaction: First, the cypridinid luciferin is activated by an enzyme to produce a peroxide intermediate, cypridinid dioxetanone (CDO), which then decomposes to generate excited oxyluciferin (OxyCLnH*). Finally, OxyCLnH* deexcites to its ground state along with emission of bright blue light. Unfortunately, the detailed mechanism of the critical step, the thermolysis of CDO, remains unknown, and it is unclear whether the light emitter is generated from a neutral form (CDOH) or anionic form (CDO(-)) of the CDO precursor. In this work, we investigated the key step in the process by modeling the thermal decompositions of both CDOH and CDO(-). The calculated results indicate that the decomposition of CDO(-) occurs via the gradually reversible charge transfer (CT)-initiated luminescence (GRCTIL) mechanism, whereas CDOH decomposes through an entropic trapping mechanism without an obvious CT process. The thermolysis of CDO(-) is sensitive to solvent effects and is energetically favorable in polar environments compared with the thermolysis of CDOH. The thermolysis of CDO(-) produces the excited oxyluciferin anion (OxyCLn(-)), which combines with a proton from the environment to form OxyCLnH, the actual light emitter for the natural system.
希氏海萤（海萤火虫）是一种生物发光甲壳类动物，其生物发光（BL）反应是许多海洋生物的典型反应，尤其是其他生物发光甲壳类动物和腔肠动物。揭示其生物发光机制对于其强发射发光团的未来应用至关重要。海萤通过三步反应产生光：首先，海萤荧光素被一种酶激活，生成过氧化物中间体——海萤二氧杂环丁酮（CDO），然后CDO分解产生激发态氧化荧光素（OxyCLnH*）。最后，OxyCLnH去激发回到基态并发出亮蓝色光。不幸的是，关键步骤CDO的热解详细机制仍然未知，并且尚不清楚发光体是由CDO前体的中性形式（CDOH）还是阴离子形式（CDO(-)）产生的。在这项工作中，我们通过对CDOH和CDO(-)的热分解进行建模来研究该过程中的关键步骤。计算结果表明，CDO(-)的分解通过逐渐可逆的电荷转移（CT）引发发光（GRCTIL）机制发生，而CDOH通过熵捕获机制分解，没有明显的CT过程。与CDOH的热解相比，CDO(-)的热解对溶剂效应敏感，并且在极性环境中能量上更有利。CDO(-)的热解产生激发态氧化荧光素阴离子（OxyCLn(-)），它与环境中的质子结合形成OxyCLnH*，这是自然系统中的实际发光体。
