title: Ground and singlet excited state pyridinic protonation of N9-methylbetacarboline in water-N,N-dimethylformamide mixtures.
abstract: The ground and the singlet excited state pyridinic protonation of 9-methyl-9H-pyrido[3,4-b]indole, MBC, in water-N,N-dimethylformamide mixtures has been studied by absorption, steady state and time resolved fluorescence measurements. These proton transfer reactions elapse by a stepwise mechanism modulated by different hydrogen bonded adducts and exciplexes formed by water molecules and the pyridinic nitrogen atom of the MBC. Based in the present and previous studies, a general mechanistic Scheme for the ground and the singlet excited state MBC pyridinic protonation has been proposed. Accordingly, in the ground state, upon increasing the water proportion of the water-N,N-dimethylformamide mixtures, a hydrogen bonded complex, HBC, its hydrogen bonded proton transfer complex, PTC, a pre-cationic complex, PC, and the cation, C, are progressively formed. In the excited state, MBC, HBC and PC behave as independent fluorophores. Excited state cations, C*, are mainly formed by direct excitation of the ground state cations and, in minor proportion, by the excited state reaction of the PTC* through the CL* exciplex.
authors.affiliation: Departamento de Química Física, Facultad de Farmacia, Universidad de Sevilla, Sevilla 41012, Spain.
authors.forename: Antonio
authors.initials: A
authors.lastname: Sánchez Coronilla
authors.forename: Carmen
authors.initials: C
authors.lastname: Carmona
authors.forename: María A
authors.initials: MA
authors.lastname: Muñoz
authors.forename: Manuel
authors.initials: M
authors.lastname: Balón
mesh_terms: D000042:Absorption; D002243:Carbolines / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D004126:Dimethylformamide / Q000737:chemistry*; D005453:Fluorescence; D006860:Hydrogen Bonding; D008956:Models, Chemical; D017672:Nitrogen Compounds / Q000737:chemistry; D011522:Protons; D013997:Time Factors; D014867:Water / Q000737:chemistry*
chemical_list: C529608:9-methyl-beta-carboline; D002243:Carbolines; D002412:Cations; D017672:Nitrogen Compounds; D011522:Protons; D014867:Water; D004126:Dimethylformamide