title: Theoretical study of the nontraditional enol-based photoacidity of firefly oxyluciferin.
abstract: A theoretical analysis of the enol-based photoacidity of oxyluciferin in water is presented. The basis for this phenomenon is found to be the hydrogen-bonding network that involves the conjugated photobase of oxyluciferin. The hydrogen-bonding network involving the enolate thiazole moiety is stronger than that of the benzothiazole phenolate moiety. Therefore, enolate oxyluciferin should be stabilized versus the phenolate anion. This difference in strength is attributed to the fact that the thiazole moiety has more potential hydrogen-bond acceptors near the proton donor atom than the benzothiazole moiety. Moreover, the phenol-based excited-state proton transfer leads to a decrease in the hydrogen-bond acceptor potential of the thiazole atoms. The ground-state enol-based acidity of oxyluciferin is also studied. This phenomenon can be explained by stabilization of the enolate anion through strengthening of a bond between water and the nitrogen atom of the thiazole ring, in an enol-based proton-transfer-dependent way.
authors.affiliation: Centro de Investigação em Química, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, R. Campo Alegre 687, 4169-007 Porto (Portugal).
authors.forename: Luís
authors.initials: L
authors.lastname: Pinto da Silva
authors.forename: Joaquim C G
authors.initials: JC
authors.lastname: Esteves da Silva
mesh_terms: D000818:Animals; D048888:Fireflies / Q000737:chemistry; D006860:Hydrogen Bonding; D007211:Indoles / Q000737:chemistry*; D008962:Models, Theoretical; D011719:Pyrazines / Q000737:chemistry*; D011789:Quantum Theory; D014867:Water / Q000737:chemistry
chemical_list: D007211:Indoles; D011719:Pyrazines; D014867:Water; C014730:oxyluciferin
keywords: enols; excited-state proton transfer; hydrogen bonding; oxyluciferin; photoacidity