title: Xanthines Studied via Femtosecond Fluorescence Spectroscopy.
abstract: Xanthines represent a wide class of compounds closely related to the DNA bases adenine and guanine. Ubiquitous in the human body, they are capable of replacing natural bases in double helices and give rise to four-stranded structures. Although the use of their fluorescence for analytical purposes was proposed, their fluorescence properties have not been properly characterized so far. The present paper reports the first fluorescence study of xanthine solutions relying on femtosecond spectroscopy. Initially, we focus on 3-methylxanthine, showing that this compound exhibits non-exponential fluorescence decays with no significant dependence on the emission wavelength. The fluorescence quantum yield (3 × 10-4) and average decay time (0.9 ps) are slightly larger than those found for the DNA bases. Subsequently, we compare the dynamical fluorescence properties of seven mono-, di- and tri-methylated derivatives. Both the fluorescence decays and fluorescence anisotropies vary only weakly with the site and the degree of methylation. These findings are in line with theoretical predictions suggesting the involvement of several conical intersections in the relaxation of the lowest singlet excited state.
authors.affiliation: LIDYL, CEA, CNRS, Université Paris-Saclay, F-91191 Gif-sur-Yvette, France. pascale.changenet-barret@polytechnique.edu.
authors.forename: Pascale
authors.initials: P
authors.lastname: Changenet-Barret
authors.affiliation: Department of Medicinal Chemistry, University of Szeged, Dóm tér 8, 6720 Szeged, Hungary. kovacs.lajos@med.u-szeged.hu.
authors.forename: Lajos
authors.initials: L
authors.lastname: Kovács
authors.affiliation: LIDYL, CEA, CNRS, Université Paris-Saclay, F-91191 Gif-sur-Yvette, France. dimitra.markovitsi@cea.fr.
authors.forename: Dimitra
authors.initials: D
authors.lastname: Markovitsi
authors.affiliation: LIDYL, CEA, CNRS, Université Paris-Saclay, F-91191 Gif-sur-Yvette, France. thomas.gustavsson@cea.fr.
authors.forename: Thomas
authors.initials: T
authors.lastname: Gustavsson
mesh_terms: D004247:DNA / Q000737:chemistry; D004563:Electrochemistry; D005453:Fluorescence; D005454:Fluorescence Polarization; D007700:Kinetics; D008745:Methylation; D011789:Quantum Theory; D012996:Solutions; D013050:Spectrometry, Fluorescence; D014970:Xanthines / Q000737:chemistry*
chemical_list: D012996:Solutions; D014970:Xanthines; D004247:DNA
keywords: electronic excited states; femtosecond spectroscopy; fluorescence; xanthines