title: UV-induced oxo --> hydroxy unimolecular proton-transfer reactions in hypoxanthine.
abstract: Monomers of hypoxanthine isolated in low-temperature Ar matrixes were studied using Fourier transform infrared spectroscopy. Two most stable tautomeric forms of hypoxanthine: oxo-N(9)-H and oxo-N(7)-H as well as a very small amount of the minor hydroxy-N(9)-H tautomer were observed in Ar matrixes directly after their deposition. UV irradiation of the matrixes induced conversion of the oxo-N(9)-H and oxo-N(7)-H tautomers of the compound into the hydroxy-N(9)-H and hydroxy-N(7)-H forms, respectively. Upon exposure of the matrixes to the UV (lambda > 270 nm) light, the oxo-N(9)-H --> hydroxy-N(9)-H phototautomeric reaction dominated strongly over the oxo-N(7)-H --> hydroxy-N(7)-H phototransformation. The latter phototautomeric reaction occurred effectively when matrix-isolated hypoxanthine was irradiated with shorter-wavelength (lambda > 230 nm) UV light. Thanks to this wavelength dependency, it was possible to clearly distinguish the oxo --> hydroxy photoreaction within the N(9)-H tautomers from the analogous phototautomeric process within the N(7)-H tautomers. All of the observed isomers of hypoxanthine (substrates and products of the photoreactions) were identified by comparison of their IR spectra with the spectra calculated at the DFT(B3LYP)/6-31++G(d,p) level of theory.
authors.affiliation: Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw, Poland.
authors.forename: Anna
authors.initials: A
authors.lastname: Gerega
authors.forename: Leszek
authors.initials: L
authors.lastname: Lapinski
authors.forename: Maciej J
authors.initials: MJ
authors.lastname: Nowak
authors.forename: Hanna
authors.initials: H
authors.lastname: Rostkowska
mesh_terms: D003198:Computer Simulation; D019271:Hypoxanthine / Q000737:chemistry* / Q000528:radiation effects*; D008956:Models, Chemical; D015394:Molecular Structure; D011522:Protons; D012680:Sensitivity and Specificity; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods; D014466:Ultraviolet Rays
chemical_list: D011522:Protons; D019271:Hypoxanthine