UV-Induced Amino → Imino Hydrogen-Atom Transfer in 1-Methylcytosine

Reva I., Nowak M. J., Lapinski L., Fausto R.

JOURNAL OF PHYSICAL CHEMISTRY B, vol.116, no.19, pp.5703-5710, 2012 (SCI-Expanded) identifier identifier identifier

  • Publication Type: Article / Article
  • Volume: 116 Issue: 19
  • Publication Date: 2012
  • Doi Number: 10.1021/jp302375u
  • Journal Name: JOURNAL OF PHYSICAL CHEMISTRY B
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.5703-5710
  • Istanbul Kültür University Affiliated: Yes

Abstract

Monomers of 1-methylcytosine, isolated in low-temperature argon matrixes, were excited with narrowband tunable UV light. Irradiation at lambda = 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 (lambda <= 308 nm) irradiation, were also observed.