title: A conical intersection controls the deactivation of the bacterial luciferase fluorophore.
abstract: The photophysics of flavins is highly dependent on their environment. For example, 4a-hydroxy flavins display weak fluorescence in solution, but exhibit strong fluorescence when bound to a protein. To understand this behavior, we performed temperature-dependent fluorescent studies on an N(5)-alkylated 4a-hydroxy flavin: the putative bacterial luciferase fluorophore. We find an increase in fluorescence quantum yield upon reaching the glass transition temperature of the solvent. We then employ multiconfigurational quantum chemical methods to map the excited-state deactivation path of the system. The result reveals a shallow but barrierless excited state deactivation path that leads to a conical intersection displaying an orthogonal out-of-plane distortion of the terminal pyrimidine ring. The intersection structure readily explains the observed spectroscopic behavior in terms of an excited-state barrier imposed by the rigid glass cavity.
authors.affiliation: Chemistry Department, Bowling Green State University, Bowling Green, OH 43403 (USA) http://www.bgsu.lcpp.com/
authors.forename: Samer
authors.initials: S
authors.lastname: Gozem
authors.forename: Ekaterina
authors.initials: E
authors.lastname: Mirzakulova
authors.forename: Igor
authors.initials: I
authors.lastname: Schapiro
authors.forename: Federico
authors.initials: F
authors.lastname: Melaccio
authors.forename: Ksenija D
authors.initials: KD
authors.lastname: Glusac
authors.forename: Massimo
authors.initials: M
authors.lastname: Olivucci
mesh_terms: D005415:Flavins; D005453:Fluorescence; D049453:Luciferases, Bacterial / Q000737:chemistry*; D008958:Models, Molecular
chemical_list: D005415:Flavins; D049453:Luciferases, Bacterial
keywords: conical intersection; flavins; fluorescence probe; internal conversion; luciferase