DNA is an Amphiphilic Polyelectrolyte

As is well known, and as already alluded to above, the association of two DNA strands into the double helix is driven by the hydrophobic interactions between the bases. Polar interactions, associated with the phosphate and carbohydrate groups, counteract the association. Hydrogen bonding and specific packing of the bases control the details of the double helix structure. 

While the electrostatic interactions of DNA have been analyzed in detail, the hydrophobic interactions have been much less discussed. In particular the balance between the polar and nonpolar interactions have a deep impact on how DNA interacts with cosolutes, including electrolytes, nonpolar molecules, surfactants, lipids and macromolecules. 

In the context of DNA-surfactant interactions we will briefly comment on the amphiphilic nature of DNA and its consequences for the solution behavior In discussing the self-assembly behavior of DNA, we begin by broadly discussing other amphiphilic compounds and their self-assembly. Amphiphilic compounds - those that have distinct hydrophilic and lipophilic parts - range from low molecular weight molecules, like surfactants and lipids, to macromolecules, consisting of synthetic graft and block copolymers, and biomacromolecules, like proteins, lipopolysacchar-ides and nucleic acids. 

Surfactant and lipid self-assembly can lead to a diverse range of aggregate structures, the type of aggregate formed being mainly determined by the chemical structure and the relative strength of the hydrophilic and lipophilic parts [49]. 

Amphiphilic/associating vater-soluble polymers, in particular block copolymers and hydrophobically modified vater-soluble polymers, have been studied extensively during the last decade and are vell understood [50, 51]. For graft copolymers that are hydrophobically modified vater-soluble polymers, vhich are common as thickeners and dispersants, the self-assembly is very different than for block copolymers. For such graft copolymers there is a strong opposing force due to the hydrophilic polymer backbone. In particular, due to the entropic penalty in folding the polymer chain, only small discrete hydrophobic micro-domains ( micelles ) are formed. 

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