56336-26-6Relevant articles and documents
Photoionization of organic phosphates by 193 nm laser light in aqueous solution: Rapid intramolecular H-transfer to the primarily formed phosphate radical. A model for ionization-induced chain-breakage in DNA?
Steenken, Steen,Goldbergerova, Ludmila
, p. 3928 - 3934 (2007/10/03)
In aqueous solution, 193 nm (6.4 eV) photolysis of inorganic and organic phosphates such as ribose-5-phosphate leads to ionization with formation of the corresponding oxygen-centered phosphate radicals, O3PO. These (oxidizing) radicals function as traps with respect to hydrogens attached to α-, β-, or, possibly, γ-carbons, whereby in the case of the β-hydrogens a six-membered transition state for transfer of the hydrogen to the phosphate oxygen is possible, leading to high rate constants (up to >5 x 107 s-1) for H-transfer in these unimolecular reactions. In the case of (deoxy)ribosephosphates the six-membered transition state is possible for transfer of the hydrogen at C4 to the phosphate group at C5 as well as at C3. In DNA, the resulting C4'-radical will undergo a rapid β-elimination of the phosphate-ester group, this step representing the DNA chain break. The apparently easy H-transfer from a carbon to a phosphate radical, by which these radicals are 'repaired', is why phosphate radicals are not observed in irradiated DNA. Insofar as hereby the C4'-radical is formed, the mechanism of DNA chain breakage is the same for the 'direct' and the 'indirect' effect.
