EPR evidence for Sigma -Radicals in Irradiated Thiothymine in a Single Crystal (CROSBI ID 477317)
Prilog sa skupa u zborniku | sažetak izlaganja sa skupa | međunarodna recenzija
Podaci o odgovornosti
Bešić, Erim ; Sanković, Krešimir ; Herak, Janko N.
engleski
EPR evidence for Sigma -Radicals in Irradiated Thiothymine in a Single Crystal
Thionucleobases have been used as instrinsic photolabels to probe the structure and organization of RNA molecules in solution and to identify the contacts between nucleic acids and proteins in nucleoprotein complexes (1). The thioanalogs of the nucleic-acid bases absorb light at long wavelengths and can be selectively photoactivated into the electronic triplet state, leading to their high affinity to crosslink to other nucleic-acid bases and amino-acid residues in contact. Here we show that thionucleobases behave different from natural nucleic-acid bases also when irradiated by radiation of much higher energy (gamma-rays). In irradiated regular (non-thiolated) nucleic-acid bases in the crystals only pi-type radicals are found. In the crystalline thionucleobases the radicals of the sigma-type are observed. The sigma-type radicals have been studied in detail in the irradiated single crystal of thiothymine. The maximum value of the g tensor coincides with the direction of the C-S bond, indicating the dominant contribution of the spin density in one of the sulfur p orbitals perpendicular to that bond. The radical is formed by ultimate release of the H-1 proton, leaving a significant spin density (about 10%) in the N(1) non-bonding sp2 atomic orbital, as concluded from the nitrogen N-1 hyperfine splitting tensor. The observation is consistent with the idea that the high-energy radiation induces ionization by knocking out one of the electrons from the sulfur non-bonding orbital. The resulting cation is neutralized by subsequent deprotonation at N-1. References: 1. Favre A., Saintome C., Fourrey J.L., Laugaa P., J.Photochem. Photobiol. B 42, 109-124 (1998). Acknowledgement: This work has been supported by the Croatian Ministry of Science and Technology.
EPR; sigma-radicals; thiothymine
nije evidentirano
nije evidentirano
nije evidentirano
nije evidentirano
nije evidentirano
nije evidentirano
Podaci o prilogu
313 - 313-x.
2000.
objavljeno
Podaci o matičnoj publikaciji
XIX International Conference on Magnetic Resonance in Biological Systems - Book of Abstracts
Banci, Lucia ; Bertini, Ivano
Firenza : München:
Podaci o skupu
XIX International Conference on Magnetic Resonance in Biological Systems - Magnetic Resonance for the Life Sciencesin the Twenty-First Century
poster
20.08.2000-25.08.2000
Firenca, Italija