title: UV-induced generation of rare tautomers of allopurinol and 9-methylhypoxanthine -- a matrix isolation FTIR study.
abstract: Monomers of allopurinol and 9-methylhypoxanthine were studied using the matrix isolation technique combined with Fourier transform infrared spectroscopy. The oxo tautomeric forms of both compounds were found to dominate in freshly deposited low-temperature argon matrices. For 9-methylhypoxanthine, a small amount of the hydroxy tautomer was also detected in an Ar matrix before any irradiation. Upon exposure of the matrices to the UV (lambda>230 nm or lambda>270 nm) light, a proton transfer photoreaction converting the oxo forms of both compounds into the corresponding hydroxy tautomers occurred. Generation of conjugated ketenes as minor photoproducts was also observed. For 4(3H)-pyrimidinone (a model compound for both allopurinol and 9-methylhypoxanthine), photoreversibility of the UV-induced oxo --> hydroxy transformation was experimentally proven by direct observation of the back hydroxy --> oxo photoreaction. The substrates (oxo tautomers) and products (hydroxy tautomers) of the observed phototransformations were identified by comparison of their IR spectra with the spectra theoretically predicted at the DFT(B3LYP)/6-31++G(d,p) level. The IR bands in the experimental spectra were assigned to the calculated normal modes.
authors.affiliation: Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw, Poland.
authors.forename: A
authors.initials: A
authors.lastname: Gerega
authors.forename: L
authors.initials: L
authors.lastname: Lapinski
authors.forename: I
authors.initials: I
authors.lastname: Reva
authors.forename: H
authors.initials: H
authors.lastname: Rostkowska
authors.forename: M J
authors.initials: MJ
authors.lastname: Nowak
mesh_terms: D000493:Allopurinol / Q000737:chemistry* / Q000528:radiation effects*; D003198:Computer Simulation; D007042:Hypoxanthines / Q000737:chemistry* / Q000528:radiation effects*; D007536:Isomerism; D008956:Models, Chemical; D015394:Molecular Structure; D011744:Pyrimidinones / Q000737:chemistry / Q000528:radiation effects; D011789:Quantum Theory; D012680:Sensitivity and Specificity; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods; D014466:Ultraviolet Rays
chemical_list: C513120:4(3H)-pyrimidinone; C513119:9-methylhypoxanthine; D007042:Hypoxanthines; D011744:Pyrimidinones; D000493:Allopurinol