Mechanistic Insight into the Chemiluminescent Decomposition of Cypridina Dioxetanone and the Chemiluminescent, Fluorescent Properties of the Light Emitter of Cypridina Bioluminescence

• DOI: 10.1021/acs.jcim.9b00614
• Publication Date: 2019-10-04T21:23:04Z
• Authors: Chun-Gang Min; Qing-Bo Liu; Yan Leng; Carla M. Magalhães; Shao-Jun Huang; Chun-Xia Liu; Xi-Kun Yang; Luís Pinto da Silva
• Keywords: Heterocyclic Compounds, 1-Ring; Light; Molecular Structure; Crustacea; 0103 physical sciences; Temperature; Animals; Humans; 01 natural sciences; Fluorescence

Cypridina bioluminescence has been increasingly used in bioimaging, bioanalysis, and biomedicine, due to high quantum yield and high signal-to-noise ratio. However, there is still no consensus regarding different aspects of the chemiluminescent mechanism of this system, which impairs the development of new applications. Herein, we have used a theoretical DFT and TD-DFT approach to (i) determine the identity of the dioxetanone species responsible for efficient chemiexcitation and (ii) identify the bioluminescent emitter and determine if light-emission occurs from the fluorescent or chemiluminescent state. Our results demonstrate that upon oxygenation of the imidazopyrazinone scaffold, a dioxetanone with a neutral amide group and a cationic guanidinopropyl group is formed. This species is efficiently chemiexcited (with no obvious charge transfer step) to the corresponding oxyluciferin with a neutral amide and cationic guanidinopropyl groups. After the "dark" chemiluminescent state, this oxyluciferin species is converted into a bright blue-emitting fluorescent state.