I have a question about the role of NaCl in the DNA extraction process. So for NaCl concentrations under 0.5M, CTAB and DNA molecules can create complexes. In those concentrations, proteins and other hydrocarbons are still soluble in water except the DNA-CTAB complex. If we raise the concentration of NaCl then the complex of CTAB-DNA will be soluble to water too. Correct me if I'm wrong until now.
So I don't understand something. Why do we use NaCl?
Let's assume that we don't add NaCl. Will the CTAB create complex with DNA or not? As I read CTAB creates ionic bonds with DNA (phosphate groups). So in this situation (without NaCl) CTAB must be able to create complex with DNA too.
So why did we use NaCl? Just to keep proteins and other hydrocarbons soluble in the water or there is something else that NaCl helps in this complex creation?
High concentration salt solution causes denaturating of proteins and precipitates them.
Sambrook and Russel, Molecular Cloning: A Laboratory Manual. is a good source too, as cited in http://www.hindawi.com/journals/bmri/2009/574398/
“Cetyltrimethylammonium bromide (CrAB) is a cationic detergent that has the useful property of precipitating nucleic acids and acidic polysaccharides from solutions of low ionic strength. Under these conditions, proteins and neutral polysaccharides remain in solution. In solutions of high ionic strength, CTAB forms complexes with proteins and all but the most acidic polysaccharides, but will not precipitate nucleic acids (Jones and Walker 1963). CTAB is therefore particularly useful for purification of DNAs from organisms that produce large quantities of polysaccharides, e.g., plants (Murray and Thompson 1980) and certain Gram-negative bacteria (including some strains of E. coli).”... Sambrook and Russel, Molecular Cloning: A Laboratory Manual 3rd Edition, CSHL
There is very active work of physico-chemical basis of this interaction which is not my "cup of tea". I just quote: "Many factors, including surfactant concentration, incubation time, salt, temperature, DNA conformation, surfactant’s chain length, and surfactant headgroup, affect the interaction between surfactant and DNA [11–16]." (https://www.hindawi.com/journals/tswj/2014/863049/#B11)
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