Structural and electronic changes of cytosine upon addition of atomic sulfur

When sulfur becomes a contaminant it may affect important biophysical and biochemical processes. In this work, we investigate the interaction of cytosine with atomic sulfur. We find two equally probable places where sulfur may link cytosine. The changes in energetics and variations in the vibrational spectra, dipole moment, charge populations and electron density with respect to isolated cytosine are quantified. The computations are performed according to the Kohn-Sham version of density functional theory. We conclude on the possibility that sulfur may locally interfere in the formation of the Watson-Crick pairs and in the stacking of contiguous nucleic acid bases of the DNA/RNA helix.