title: UV-induced amino → imino hydrogen-atom transfer in 1-methylcytosine.
abstract: Monomers of 1-methylcytosine, isolated in low-temperature argon matrixes, were excited with narrowband tunable UV light. Irradiation at λ = 314 nm resulted in syn-anti photoisomerizations between the two minor imino-oxo forms of the compound, while the dominating amino-oxo form stayed intact. Subsequent irradiations at 308 nm (as well as at shorter wavelengths) led to the amino → imino hydrogen-atom transfer converting the biologically relevant amino-oxo tautomer into the imino-oxo forms. This is the first report on the amino → imino phototautomerism in 1-methylcytosine. The observed UV-induced syn-anti photoisomerizations within the imino-oxo forms of 1-methylcytosine were found to lead to photostationary states. The photostationary [syn]/[anti] population ratio depended on the wavelength of the exciting UV light. This dependence was not monotonous. Spectral indications of the open-ring isocyanate product, generated from the amino-oxo tautomer upon UV (λ ≤ 308 nm) irradiation, were also observed.
authors.affiliation: Institute of Physics, Polish Academy of Sciences , Al. Lotnikow 32/46, 02-668 Warsaw, Poland.
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: D001128:Argon; D003080:Cold Temperature; D003198:Computer Simulation; D003596:Cytosine / Q000031:analogs & derivatives* / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry*; D007536:Isomerism; D008745:Methylation; D015394:Molecular Structure; D013055:Spectrophotometry, Infrared; D014466:Ultraviolet Rays
chemical_list: C031532:1-methylcytosine; D001128:Argon; D006859:Hydrogen; D003596:Cytosine