title: The reaction mechanism for the high quantum yield of Cypridina (Vargula) bioluminescence supported by the chemiluminescence of 6-aryl-2-methylimidazo[1,2-a]pyrazin-3(7H)-ones (Cypridina luciferin analogues).
abstract: To establish the reaction mechanism of the high-quantum-yield bioluminescence in Cypridina (Vargula), we investigated the chemiluminescence of 6-aryl-2-methylimidazo[1,2-a]pyrazin-3(7H)-ones (1H) as Cypridina luciferin analogues in DMSO-1,1,3,3-tetramethylguanidine and in diglyme-acetate buffer. We found that the chemiluminescence of 1H with an electron-donating aryl group, such as a 4-(dimethylamino)phenyl, 3-indolyl or 3-(1-methyl)indolyl group, gave a high quantum yield (Phi(CL)) in diglyme-acetate buffer. This indicates that the reaction mechanism producing this high Phi(CL) involves the chemiexcitation of a neutral dioxetanone intermediate possessing an electron-donating aryl group to the singlet excited state of neutral acetamidopyrazine (the light emitter). In addition, we investigated the fluorescence of acetamidopyrazines and performed DFT calculations for neutral dioxetanones and the transition states (TS) of the dioxetanone's decomposition. The results made it clear that the electron-donating aryl group gives the TS and the singlet-excited acetamidopyrazine (S(1)) a strong intramolecular charge transfer (ICT) character, and their similar ICT character leads to the ICT TS --> S(1) route in the charge transfer-induced luminescence (CTIL) mechanism for efficient chemiexcitation. The reaction mechanism of the chemiluminescence of 1H can explain the highly efficient chemiexcitation of Cypridina bioluminescence.
authors.affiliation: Department of Applied Physics and Chemistry, The University of Electro-Communications, Chofu, Tokyo 182-8585, Japan. hirano@pc.uec.ac.jp
authors.forename: Takashi
authors.initials: T
authors.lastname: Hirano
authors.forename: Yuto
authors.initials: Y
authors.lastname: Takahashi
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kondo
authors.forename: Shojiro
authors.initials: S
authors.lastname: Maki
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kojima
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ikeda
authors.forename: Haruki
authors.initials: H
authors.lastname: Niwa
mesh_terms: D000818:Animals; D003445:Crustacea; D049449:Luminescence; D011719:Pyrazines / Q000737:chemistry*; D011789:Quantum Theory; D021241:Spectrometry, Mass, Electrospray Ionization; D013055:Spectrophotometry, Infrared
chemical_list: D011719:Pyrazines; C048193:2-methyl-6-phenyl-3,7-dihydroimidazo(1,2-a)pyrazin-3-one