title: DNA photoreacts by nucleobase ring cleavage to form labile isocyanates.
abstract: Differential infrared absorption spectroscopy was used to study the formation of isocyanates and further photo-products in the oligonucleotides dG10, dC10 and dT10 and in their mononucleosides by ultraviolet light at 266 nm. We find that α-cleavage takes place in oligonucleotides and mononucleosides both in films and in solution. The very intense and spectrally isolated isocyanate (N=C=O) asymmetric stretch vibration at 2277 cm(-1) is used as a spectroscopic marker for detection of the photo-product. The band disappears upon reaction with small amounts of water vapour as expected for isocyanates. Quantum yields for isocyanate formation by nucleobase ring cleavage in the α-position to the carbonyl group are ∼5 × 10(-5) in the mononucleosides and up to 5 × 10(-4) in the oligonucleotides. In the mixed oligonucleotides dG10/dC10 and dA10/dT10 the quantum yield of α-cleavage drops by a factor of 10 compared to the single oligonucleotides. Implications for DNA repair and photo-induced DNA-protein cross-linking via isocyanate reaction with NH2 groups of amino acids are discussed.
authors.affiliation: Department of Physical Chemistry, Heinrich-Heine-University, University Street-1, D-40225 Düsseldorf, Germany. kleinermanns@uni-duesseldorf.de.
authors.forename: Laura
authors.initials: L
authors.lastname: Buschhaus
authors.forename: Josefin
authors.initials: J
authors.lastname: Rolf
authors.forename: Karl
authors.initials: K
authors.lastname: Kleinermanns
mesh_terms: D004247:DNA / Q000737:chemistry*; D004249:DNA Damage; D006151:Guanosine / Q000737:chemistry; D017953:Isocyanates / Q000737:chemistry*; D010782:Photolysis; D014466:Ultraviolet Rays
chemical_list: D017953:Isocyanates; D006151:Guanosine; D004247:DNA