title: Spontaneous tunneling and near-infrared-induced interconversion between the amino-hydroxy conformers of cytosine.
abstract: Spontaneous and near-infrared/infrared (NIR/IR)-induced interconversions between two amino-hydroxy conformers of monomeric cytosine have been investigated for the compound isolated in a low-temperature argon matrix. Combined use of a laser source (which provides narrowband NIR radiation) and a broadband NIR/IR source of excitation light allowed a detailed investigation of mutual conversions of the two conformers in question. The experiments carried out within the current work demonstrated that upon broadband NIR/IR irradiation (with the IR source of FTIR spectrometer) the population ratio of the two amino-hydroxy conformers changes towards a ratio corresponding to a photostationary state. Evolution of the conformer population ratio towards the photostationary ratio occurred independent of the initial ratio of conformers, which could be prepared by a population shift (in favor of one of the forms) induced by narrowband NIR excitation. Moreover, spontaneous tunneling conversion of the higher-energy conformer into a lower-energy form was observed for cytosine isolated in a low-temperature argon matrix kept in the dark. This process is slow and occurs on a time scale of days. The tunneling process, studied for matrix-isolated cytosine, clearly follows a dispersive type of kinetics rather than the classical monoexponential kinetics.
authors.affiliation: Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal.
authors.forename: Igor
authors.initials: I
authors.lastname: Reva
authors.forename: Maciej J
authors.initials: MJ
authors.lastname: Nowak
authors.forename: Leszek
authors.initials: L
authors.lastname: Lapinski
authors.forename: Rui
authors.initials: R
authors.lastname: Fausto
mesh_terms: D000588:Amines / Q000737:chemistry; D003596:Cytosine / Q000031:analogs & derivatives* / Q000737:chemistry; D017665:Hydroxyl Radical / Q000737:chemistry; D007259:Infrared Rays; D008968:Molecular Conformation; D055668:Photochemical Processes; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D000588:Amines; D017665:Hydroxyl Radical; D003596:Cytosine