Chemistry Research Unit (CIQUP), Institute of Molecular Sciences (IMS), Faculty of Sciences of University of Porto (FCUP), Rua do Campo Alegre 687, 4169-007 Porto, Portugal.
LACOMEPHI, GreenUPorto, Department of Geosciences, Environment and Territorial Planning, Faculty of Sciences of University of Porto (FCUP), Rua do Campo Alegre 687, 4169-007 Porto, Portugal.
J Phys Chem A. 2022 Jun 9;126(22):3486-3494. doi: 10.1021/acs.jpca.2c01835. Epub 2022 May 25.
Coelenterazine and other imidazopyrazinones are important bioluminescent substrates widespread in marine species and can be found in eight phyla of luminescent organisms. Light emission from these systems is caused by the formation and subsequent thermolysis of a dioxetanone intermediate, whose decomposition allows for efficient chemiexcitation to singlet excited states. Interestingly, some studies have also reported the involvement of unexpected dioxetane intermediates in the chemi- and bioluminescent reactions of Coelenterazine, albeit with little information on the underlying mechanisms of these new species. Herein, we have employed a theoretical approach based on density functional theory to study for the first time the thermolysis reaction and chemiexcitation profile of two Coelenterazine dioxetanes. We have found that the thermolysis reactions of these species are feasible but with relevant energetic differences. More importantly, we found that the singlet chemiexcitation profiles of these dioxetanes are significantly less efficient than the corresponding dioxetanones. Furthermore, we identified triplet chemiexcitation pathways for the Coelenterazine dioxetanes. Given this, the chemiexcitation of these dioxetanes should lead only to minimal luminescence. Thus, our theoretical investigation of these systems indicates that the thermolysis of these dioxetanes should only provide "dark" pathways for the formation of nonluminescent degradation products of the chemi- and bioluminescent reactions of Coelenterazine and other imidazopyrazinones.
腔肠素和其他咪唑并吡嗪酮是海洋物种中广泛存在的重要生物发光底物，可在发光生物的 8 个门中找到。这些系统的发光是由二氧杂环戊酮中间体的形成和随后的热解引起的，其分解允许高效的化学激发到单重激发态。有趣的是，一些研究还报道了腔肠素的化学发光和生物发光反应中涉及到意想不到的二氧杂环丁烷中间体，尽管对这些新物种的潜在机制知之甚少。在此，我们首次采用基于密度泛函理论的理论方法研究了两种腔肠素二氧杂环丁烷的热解反应和化学激发特性。我们发现这些物质的热解反应是可行的，但能量差异较大。更重要的是，我们发现这些二氧杂环丁烷的单重化学激发特性明显不如相应的二氧杂环戊酮。此外，我们还确定了腔肠素二氧杂环丁烷的三重态化学激发途径。鉴于此，这些二氧杂环丁烷的化学激发应该只会导致最小的发光。因此，我们对这些体系的理论研究表明，这些二氧杂环丁烷的热解应该只能为腔肠素和其他咪唑并吡嗪酮的化学发光和生物发光反应形成非发光降解产物提供“黑暗”途径。
