C5'- and C3'-sugar radicals produced via photo-excitation of one-electron oxidized adenine in 2'-deoxyadenosine and its derivatives.
We report that photo-excitation of one-electron-oxidized adenine [A(-H)*] in dAdo and its 2'-deoxyribonucleotides leads to formation of deoxyribose sugar radicals in remarkably high yields. Illumination of A(-H)* in dAdo, 3'-dAMP and 5'-dAMP in aqueous glasses at 143 K leads to 80-100% conversion to sugar radicals at C5' and C3'. The position of the phosphate in 5'- and 3'-dAMP is observed to deactivate radical formation at the site of substitution. In addition, the pH has a crucial influence on the site of sugar radical formation; e.g. at pH approximately 5, photo-excitation of A(-H)* in dAdo at 143 K produces mainly C5'* whereas only C3'* is observed at high pH approximately 12. 13C substitution at C5' in dAdo yields 13C anisotropic couplings of (28, 28, 84) G whose isotropic component 46.7 G identifies formation of the near planar C5'*. A beta-13C 16 G isotropic coupling from C3'* is also found. These results are found to be in accord with theoretically calculated 13C couplings at C5' [DFT, B3LYP, 6-31(G) level] for C5'* and C3'*. Calculations using time-dependent density functional theory [TD-DFT B3LYP, 6-31G(d)] confirm that transitions in the near UV and visible induce hole transfer from the base radical to the sugar group leading to sugar radical formation.
Department of Chemistry, Oakland University, Rochester, MI 48309, USA.
Amitava
A
Adhikary
David
D
Becker
Sean
S
Collins
Jessica
J
Koppen
Michael D
MD
Sevilla
D000225:Adenine / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry; D003838:Deoxyadenine Nucleotides / Q000737:chemistry; D003839:Deoxyadenosines / Q000737:chemistry*; D003855:Deoxyribose / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D004583:Electrons; D005609:Free Radicals / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008027:Light; D008958:Models, Molecular; D010084:Oxidation-Reduction; D011522:Protons; D013056:Spectrophotometry, Ultraviolet
D003838:Deoxyadenine Nucleotides; D003839:Deoxyadenosines; D005609:Free Radicals; D011522:Protons; C028191:2'-deoxy-3'-adenosine monophosphate; D003855:Deoxyribose; C012873:2'-deoxy-5'-adenosine monophosphate; D002244:Carbon; D000225:Adenine; C058118:2'-deoxyadenosine