Re: Ammonia and Ureas' affect on DNA?

I apologize for taking so long to answer the question.

Denaturing agents such as urea and formamide (HCONH2) are called chaotropic 
agents because they tend to disrupt water's ability to solvate DNA's 
negatively charged phosphate groups.  The negative charges, then, repel each 
other more strongly and induce a "rodlike" conformation of the DNA.
(the C2' endo configuration of the ribose ring is even more exaggerated and 
the phospates are even  further apart) 

In order to oppose this destabilizing affect, I would suggest increasing the 
ionic strength of the solvent (salt), so that positively charged monovalent 
ions can quench the negative charges.

Thanks for being so patient,
Elena Rodriguez