How does guanidium denature DNA?
Guanidium is a chaotrope i.e it increases the entropy in the solution. It doesn't disrupt hydrophobic interactions. Guanidium and urea act by forming hydrogen bonds. They can bond with both the dissolved macromolecule and water. The water molecules are arranged as a shell around the hydrophobic regions so as to contain it, which leads to the reduction of entropy. This containment causes hydrophobic regions to come together and give rise to a pseudo-interaction (hydrophobic interaction. See the figure below). Guanidium interacts with the water shell and disorders it, thereby reducing the hydrophobic effect.
Guanidium can also interact with macromolecules directly, by forming hydrogen bonds. In this process they can disrupt the normal H-bonds in the macromolecule.