Chemistry Research Unit (CIQUP), Department of Chemistry and Biochemistry, Faculty of Sciences of University of Porto , R. Campo Alegre 687, 4169-007 Porto, Portugal.
LACOMEPHI, Department of Geosciences, Environment and Territorial Planning, Faculty of Sciences of University of Porto , R. Campo Alegre 687, 4169-007 Porto, Portugal.
J Phys Chem B. 2017 Aug 24;121(33):7862-7871. doi: 10.1021/acs.jpcb.7b06295. Epub 2017 Aug 9.
The bioluminescent reaction of the "sea firefly" Cypridina hilgendorfii is a prototypical system for marine bioluminescence, as its substrate possesses an imidazopyrazinone core that is a common link among organisms of eight phyla. The elucidation of the mechanism behind Cypridina bioluminescence is essential for future applications in bioimaging, biomedicine, and bioanalysis. In this study we have investigated the key step of chemiexcitation with a combined experimental and theoretical approach. The obtained results indicate that neutral dioxetanone is responsible for efficient chemiexcitation, as the thermolysis of this species gives access to a long region of the potential energy surface (PES), where the ground and excited singlet states are degenerated. Contrary to expected, neither chemically induced electron-exchange luminescence (CIEEL) nor charge transfer-initiated luminescence (CTIL) can be used to explain imidazopyrazinone-based bioluminescence, as there is no clear relationship between electron (ET)/charge (CT) transfer (occurring between the electron-rich moiety and dioxetanone) and chemiexcitation. Attractive electrostatic interactions between the CO and oxyluciferin moieties allow neutral dioxetanone to spend time in the PES region of degeneracy, while repulsive interactions for anionic dioxetanone lead to a quicker CO detachment.
“海萤”Cypridina hilgendorfii 的生物发光反应是海洋生物发光的典型体系，因为其底物具有咪唑并吡嗪酮核心，这是 8 个门的生物之间的共同联系。阐明 Cypridina 生物发光背后的机制对于未来在生物成像、生物医学和生物分析中的应用至关重要。在这项研究中，我们采用实验和理论相结合的方法研究了化学激发的关键步骤。所得结果表明，中性二氧杂环丁酮是负责有效化学激发的原因，因为该物质的热解可以进入势能面（PES）的长区域，其中基态和激发单线态是简并的。与预期相反，化学诱导的电子交换发光（CIEEL）和电荷转移引发的发光（CTIL）都不能用来解释基于咪唑并吡嗪酮的生物发光，因为电子（ET）/电荷（CT）转移（发生在富电子部分和二氧杂环丁酮之间）与化学激发之间没有明显的关系。CO 和氧化荧光素部分之间的吸引力静电相互作用使中性二氧杂环丁酮能够在简并 PES 区域花费时间，而对于阴离子二氧杂环丁酮的排斥相互作用导致 CO 更快地脱离。
