A Computational Investigation of the Equilibrium Constants for the Fluorescent and Chemiluminescent States of Coelenteramide.
In spite of recent advances in understanding the mechanism of coelenterate bioluminescence, there is no consensus about which coelenteramide specie and/or state are the light emitter. In this study, a systematic investigation of the geometries and spectra of all possible light emitters has been performed at the TD ωB97XD/6-31+G(d) level of theory, including various fluorescent and chemiluminescent states in vacuum, in a hydrophobic environment and in aqueous solution. To deduce the most probable form of the fluorescent and chemiluminescent coelenteramide emitter, the equilibrium constants for the fluorescent and chemiluminescent states connecting the various species have been calculated. ωB97XD gives a qualitatively good description of fluorescent and chemiluminescent structures. Coelenteramide is formed in a "dark" chemiluminescent state and must evolve to a bright fluorescent state. Moreover, the photoacidity of the phenol group is significantly higher in the fluorescent state than in the chemiluminescent state, which allows the formation of phenolate coelenteramide and clarifies its role as the bioluminescent emitter.
Research Center for Analysis and Measurement, Kunming University of Science and Technology, Kunming, 650093, P. R. China.
Chun-Gang
CG
Min
Centro de Investigaçäo em Química (CIQ-UP), Departamento de Química e Bioquímica, Faculdade de Ciências da Universidade do Porto, Rua Campo Alegra 687, 4169-007, Porto, Portugal.
Luís
L
Pinto da Silva
Centro de Investigaçäo em Química (CIQ-UP), Departamento de Química e Bioquímica, Faculdade de Ciências da Universidade do Porto, Rua Campo Alegra 687, 4169-007, Porto, Portugal.
Joaquim C G
JC
Esteves da Silva
Research Center for Analysis and Measurement, Kunming University of Science and Technology, Kunming, 650093, P. R. China.
Xi-Kun
XK
Yang
Research Center for Analysis and Measurement, Kunming University of Science and Technology, Kunming, 650093, P. R. China.
Shao-Jun
SJ
Huang
Institute of Theoretical Chemistry, Jilin University, Changchun, 130023, P. R. China.
Ai-Min
AM
Ren
Research Center for Analysis and Measurement, Kunming University of Science and Technology, Kunming, 650093, P. R. China.
Yan-Qin
YQ
Zhu
D044482:Benzeneacetamides / Q000737:chemistry*; D005453:Fluorescence; D049449:Luminescence; D015394:Molecular Structure; D011719:Pyrazines / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics
D044482:Benzeneacetamides; D011719:Pyrazines; C542661:coelenteramide
acidity; density functional calculations; fluorescence; luminescence; photochemistry