title: Singlet excited state pyridinic deprotonation of the N9-methylbetacarboline cations in aqueous sodium hydroxide solutions.
abstract: The singlet excited state pyridinic deprotonation of the 9-methyl-9H-pyrido[3,4-b]indole, MBC, cations has been studied in aqueous NaOH solutions by absorption, steady state and time resolved fluorescence measurements. This excited state reaction proceeds through a stepwise mechanism involving different ground and excited state hydrogen bonded MBC-(water)n complexes. Thus, in aqueous NaOH solutions of MBC above pH 8, two ground state hydrogen bonded MBC-water adducts, namely PC and PTC, coexist in equilibrium. Upon excitation, the PC behaves as an independent fluorophore, whereas the PTC reacts with water molecules during its excited state lifetime to give the intermediate CL*. This exciplex is the precursor of the excited state cation, C*. In almost all the pH range, C* is practically the only existing species in the singlet excited state of MBC. In concentrated NaOH solutions beyond the pH range, C* deprotonates giving CL* and PTC* species.
authors.affiliation: Departamento de Química Física, Facultad de Farmacia, Universidad de Sevilla, 41012 Sevilla, Spain.
authors.forename: Antonio Sánchez
authors.initials: AS
authors.lastname: 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*; D004126:Dimethylformamide; D005559:Formamides / Q000737:chemistry; D011522:Protons; D011725:Pyridines / Q000737:chemistry*; D012972:Sodium Hydroxide / Q000737:chemistry*; D012996:Solutions; D013050:Spectrometry, Fluorescence; D014867:Water / Q000737:chemistry*
chemical_list: C529608:9-methyl-beta-carboline; D002243:Carbolines; D005559:Formamides; D011522:Protons; D011725:Pyridines; D012996:Solutions; D014867:Water; D012972:Sodium Hydroxide; D004126:Dimethylformamide
references.citation: Photochem Photobiol. 2002 Sep;76(3):239-46
references.pmid: 12403443
references.citation: J Phys Chem A. 2005 Jan 13;109(1):13-35
references.pmid: 16839085
references.citation: J Am Chem Soc. 2007 Nov 7;129(44):13412-20
references.pmid: 17935322
references.citation: Chemphyschem. 2006 Sep 11;7(9):1848-70
references.pmid: 16929553
references.citation: J Fluoresc. 2009 Nov;19(6):1025-35
references.pmid: 19536642
references.citation: Adv Heterocycl Chem. 1964;3:79-207
references.pmid: 5332970
references.citation: Science. 2005 Oct 7;310(5745):83-6
references.pmid: 16210532