title: Unimolecular photochemistry of 4-thiouracils.
abstract: Unimolecular phototautomeric reactions in 4-thiouracil, 1-methyl-4-thiouracil and 6-aza-4-thiouracil were studied using the matrix-isolation technique combined with infrared absorption spectroscopy. For monomers of these compounds, isolated in solid argon at 10 K, an intramolecular proton-transfer photoreaction was observed. Upon UV (lambda > 345 nm) irradiation, the initial oxo-thione forms of 4-thiouracils were converted into the corresponding oxo-thiol tautomers. The photogenerated oxo-thiol isomers were identified by comparing their experimental IR spectra with the spectra theoretically calculated at the DFT(B3LYP)/6-311++G(2d,p) level. Good agreement between the observed and predicted pattern of spectral bands allowed a reliable identification. This is the first report on experimental observation of isomeric forms of 4-thiouracils other than the canonical oxo-thione tautomers.
authors.affiliation: Institute of Physics, Polish Academy of Sciences, Warsaw, Poland.
authors.forename: Artem
authors.initials: A
authors.lastname: Khvorostov
authors.forename: Leszek
authors.initials: L
authors.lastname: Lapinski
authors.forename: Hanna
authors.initials: H
authors.lastname: Rostkowska
authors.forename: Maciej J
authors.initials: MJ
authors.lastname: Nowak
mesh_terms: D001372:Aza Compounds / Q000737:chemistry; D007536:Isomerism; D015394:Molecular Structure; D010777:Photochemistry; D013889:Thiouracil / Q000031:analogs & derivatives* / Q000737:chemistry
chemical_list: D001372:Aza Compounds; C029037:1,3-dimethyl-4-thiouracil; C114719:4-thiouracil; D013889:Thiouracil