A theoretical study on the role of stability of cytosine and its tautomers in DNA (deoxyribonucleic acid), and investigation of interactions of Na, K, Mg, Ca, Zn metal ions and OH radical with cytosine tautomers.

In the present study, 21 cytosine tautomers were investigated so that some tautomers were reported for the first time in the gas phase and aqueous solution. C tautomer was the most stable tautomer in gas phase but C was the most stable structure in aqueous solution. The potential energy surface of all trajectories was determined for 21 tautomers and 22 transition states. Also, interactions of cytosine tautomers with Na, K, Mg, Ca and Zn metal ions were studied in gas phase and aqueous solution. Three types of interactions among metal ions and (N1 and O10), (N3 and O10) and (N3 and N9) of cytosine tautomers were investigated. The study of interaction energies of all complexes showed the stability of complexes in which interactions among Mg and Zn with tautomers were stronger than interactions among Ca, Na and K with tautomers, respectively. Some interactions of metal ions with cytosine tautomers made the most stable tautomers. So, the stability of rare tutomeric forms had a significant effect on stabilization of anomalous DNA (deoxyribonucleic acid) double helix and spontaneous mutations. Also, one of the most important causes of mutations in DNA (deoxyribonucleic acid) was the reaction of OH radical with nucleotide bases. So, interactions of OH radical with cytosine and its tautomers were investigated in gas phase and aqueous solution.Communicated by Ramaswamy H. Sarma.