Chemistry Research Unit (CIQUP), Department of Chemistry and Biochemistry, Faculty of Sciences of University of Porto, R. Campo Alegre 687, 4169-007 Porto, Portugal; Master in Oncology, Institute of Biomedical Sciences Abel Salazar - University of Porto (ICBAS-UP), Porto, Portugal.
LACOMEPHI, GreenUP, Department of Geosciences, Environment and Territorial Planning, Faculty of Sciences of University of Porto, R. Campo Alegre 687, 4169-007 Porto, Portugal; Chemistry Research Unit (CIQUP), Environment and Territorial Planning, Faculty of Sciences of University of Porto, R. Campo Alegre 687, 4169-007 Porto, Portugal.
J Photochem Photobiol B. 2019 Jan;190:21-31. doi: 10.1016/j.jphotobiol.2018.11.006. Epub 2018 Nov 13.
Imidazopyrazinone is a typical scaffold present in marine bioluminescence, in which thermal energy is converted into excitation energy in an enzyme-catalyzed reaction. In fact, the imidazopyrazinone scaffold is a common link among organisms of eight phyla. The characterization of the light emission mechanism is essential for the development of future applications in bioimaging, bioanalysis and biomedicine. Herein, we have studied the chemiluminescent reaction of three commercially-available imidazopyrazinones (Cypridina luciferin, Coelenterazine and Coelenterazine-e) in several aprotic solvents at different pH. We have found that at acidic pH only DMF and DMSO consistently present high light emission, while chemiluminescence in other solvents is negligible. We have attributed this to the inability of most solvents to allow for the deprotonation of the imidazopyrazinone core, thereby preventing the oxygenation step. We have also observed that increasing the pH of the solution leads to the inhibition of chemiluminescence, which we attributed to the deprotonation of the dioxetanone intermediate, as the neutral species is the one associated with efficient chemiexcitation. We have also observed that the pK of dioxetanone increases with the dielectric constant of the medium. Finally, our work indicated that the chemiexcitation yield increases with increasing polarity of the medium, due to a reduced transition dipole moment associated with S → S transition.
咪唑并吡嗪酮是海洋生物发光中典型的支架，其中热能在酶催化反应中转化为激发能。事实上，咪唑并吡嗪酮支架是八个门的生物之间的常见联系。发光机制的特征对于未来在生物成像、生物分析和生物医学中的应用的发展至关重要。在此，我们研究了三种市售的咪唑并吡嗪酮（海萤荧光素、腔肠素和腔肠素-e）在不同 pH 值的几种非质子溶剂中的化学发光反应。我们发现，在酸性 pH 值下，只有 DMF 和 DMSO 始终具有较高的发光强度，而在其他溶剂中的化学发光可以忽略不计。我们将其归因于大多数溶剂无法使咪唑并吡嗪酮核心去质子化，从而阻止了氧化步骤。我们还观察到，随着溶液 pH 值的增加，化学发光会受到抑制，我们将其归因于二氧戊环酮中间体的去质子化，因为中性物质与有效的化学激发有关。我们还观察到，二氧戊环酮的 pK 值随着介质介电常数的增加而增加。最后，我们的工作表明，由于与 S → S 跃迁相关的过渡偶极矩减小，化学激发产率随着介质极性的增加而增加。
