title: Theoretical photodynamic study of the photoprotolytic cycle of firefly oxyluciferin.
abstract: Firefly oxyluciferin presents a pH-sensitive fluorescence in aqueous solutions. Its fluorescence spectra are composed of two green peaks at different pH values, despite the enolate anion being the only emitter. A computational approach was used to further elucidate the photoprotolytic cycle of oxyluciferin and investigate its pH sensitivity. It was found that oxyluciferin forms π-π stacking complexes both in the ground and excited states, at basic and acidic/neutral pH. However, at different pH values, these complexes adopt a different conformation, which explains the lower energy of the emission at acidic/neutral pH, in comparison with the emission at basic pH.
authors.affiliation: Centro de Investigação em Química, Departamento de Química e Bioquímica, Faculdade de Ciências da Universidade do Porto, R. Campo Alegre 687 4169-007 Porto, Portugal.
authors.forename: Luís
authors.initials: L
authors.lastname: Pinto da Silva
authors.forename: Ron
authors.initials: R
authors.lastname: Simkovitch
authors.forename: Dan
authors.initials: D
authors.lastname: Huppert
authors.forename: Joaquim C G
authors.initials: JC
authors.lastname: Esteves da Silva
mesh_terms: D000818:Animals; D048888:Fireflies / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007211:Indoles / Q000737:chemistry*; D008958:Models, Molecular; D011719:Pyrazines / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics
chemical_list: D007211:Indoles; D011719:Pyrazines; C014730:oxyluciferin
keywords: complexes; enolate species; firefly oxyluciferin; pH-sensitive fluorescence; photoprotolytic cycle