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Cytosine in All Its Forms


​As a building block in DNA and RNA, cytosine possesses numerous isomers with the same molecular formula, but different structural formulas or distinct space configurations. An international consortium, of which IRAMIS is a member, was able to identify five of these forms by combining computer simulations of quantum chemistry and UV photonization imaging carried out at the SOLEIL synchrotron facility.

Published on 21 March 2017

Cytosine (C4H5N3O) is a nucleobase that is paired with guanine in DNA and RNA molecules. In living organisms, several isomeric forms of cytosine can coexist. Although they are close in energy, their chemical properties and, therefore, their biological functions can be completely different, which makes their study quite challenging.

The researchers in the consortium were able to identify five isomers of cytosine by combining ab initio simulations and experiments carried out on the DESIRS (Dichroism and Spectroscopy through Interaction with Synchrotron Radiation) beamline of the SOLEIL synchrotron facility, equipped with an electron-ion coincidence double-imaging spectrometer. They were able to determine thermochemical and structural data for these isomers. Their results provide valuable information for the scientists to deepen their understanding of the chemical reactivity of DNA or RNA induced by either natural or therapeutic radiation.

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