Naslov
EPR evidence for Sigma -Radicals in Irradiated Thiothymine in a Single Crystal

Autori
Bešić, Erim ; Sanković, Krešimir ; Herak, Janko N.

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
XIX International Conference on Magnetic Resonance in Biological Systems - Book of Abstracts / Banci, Lucia ; Bertini, Ivano - Firenza : München, 2000, 313 - 313

Skup
XIX International Conference on Magnetic Resonance in Biological Systems - Magnetic Resonance for the Life Sciencesin the Twenty-First Century

Mjesto i datum
Firenca, Italija, 20.08.2000. - 25.08.2000

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
EPR; sigma-radicals; thiothymine

Sažetak
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.

Izvorni jezik
Engleski

Znanstvena područja
Temeljne medicinske znanosti

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