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Flexible Single stranded DNA (ssDNA) molecules can adopt different conformations in the presence of salt, i.e, a source of positively charged DNA counterions. Using atomistic molecular dynamics simulations we show that ssDNA first adopts a collapsed coil like state when the concentration of a divalent salt (MgCl2) is less but re-expands when the concentration is increased due to overcharging of the DNA. 1 Depending on the salt concentration of the medium, DNA bases which do not obey the native sequence connectivity may get stacked to each other and contribute to the DNA chain compaction. The persistence of such non-sequentially stacked base pairs is also helpful in understanding the pattern of adsorption of nucleobases on the surface of rigid single – walled carbon nanotubes (CNT). 2 At higher ionic strength of the medium DNA bases are engaged in self-stacking and are bound weakly to the CNT whereas at a lower concentration of the salt ssDNA prefers to wrap around it. The distribution of nucleobases in an ssDNA – SWCNT hybrid finds relevance in CNT mediated gene delivery processes where subsequent unwrapping of the gene from its carrier is anticipated across the cell membrane tuned by an existing salt concentration gradient and other physiological factors such as pH and temperature. 3 In a separate study we analyze the unzipping of a non-natural nucleic acid assisted by carbon nanotube. 4 |