UV-induced oxo --> hydroxy unimolecular proton-transfer reactions in hypoxanthine.
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.
Gerega
Anna
A
Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw, Poland.
Lapinski
Leszek
L
Nowak
Maciej J
MJ
Rostkowska
Hanna
H
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
D011522:Protons; D019271:Hypoxanthine