What is "salting out"?

Question

in my textbook it gives an explanation which is really confusing!!!! can someone please explain this to me in a really *simple* way?

The solubility of macromolecules (such as proteins) in aqueous solution is maintained by an ordered layer of water molecules. Salt ions vary in their ability to ‘compete’ for electrostatic interaction with water molecules (the so-called ‘Hofmeister series’) – ammonium and sulfate ions are more effective than many other ions and hence high concentrations of ammonium sulfate are commonly used to precipitate macromolecules (eg proteins) by competing for water molecules – the macromolecules lose their ‘hydration’, aggregate together and precipitate out of solution (often referred to as ‘salting out’).

thank u!! (:

Answer 1

To put it simply:

- Proteins dissolve in water because of the polar NH2 and COOH end groups as well as the NH-CO peptide bonds.
- Adding a salt to a solution of dissolved protein displaces the proteins out of solution to form the precipitate.
- This occurs because the salt has a greater affinity for the water molecules (i.e. the ions of the salt have a greater charge density), hence they pull the charged water molecules away from the proteins, breaking intermolecular hydrogen bonds in the process.
- Once all the water is pulled away, the molecule is rendered insoluble, and precipitates out.
- Hence it is in effect 'salted out' of the solution.

Answer 2

I will do my best to explain it to you.

Exactly as the text is telling you the solubilization of a molecule is only possible when solvent particles surround the molecule and in that moment it is said that the molecule is "solvated" or that it has been "dissolved". This applies for any chemical compound not just macromolecules.

In the case of "salting out" phenomenon, the ions of a salt are added to the system macromolecule - water and in that precise moment, those ions "runs" through seeing the chance of get stuck to the great molecule, They compete with the water rmolecule to take their place in and they got it !!

As the text is telling you, some ions are more able to displace water and they bound to the chemical groups that allows the linkage. As the ions displace the water, the protein begins to lose "support" in the vast ocean of water molecules and begins a process of change in its structure (called denaturation) that causes that the macromolecule precipitates within the system. Normally, "salting out" happens when salt concentrations are high.

Curiosly there another phenomenon called "salting in" which is the opposite of the former one. Addition of low amounts of salt allows the protein to get more solubilized in the water. In this case, the ions open the structure of the macromolecule and more water can bound to the structure.

Hope it has helped!

Good luck!

Answer 3

More or less, the idea is that you add salt to a solution of proteins and the salt will have a stronger affinity for the water molecules. This will force the proteins to be attracted to one another (by Van Der Waals forces) and hence proteins will percipitate out. Since not all proteins are the same, each protein will have its own affinity for water molecules and so some proteins may require much more salt than other proteins to percepitate. For this reason, this biochemical technique is a very good for crude purification.

Hope that helps

Answer 4

Simple

Salt ions attracts water molecule

High concentration of ammonium sulfate(ions) attracts higher amount of water molecules from the protein and thus the protein molecule gets dehydrated, protein molecules bonded together and thus the concentration of the protein molecules gets increased.

This is called salting out

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Answer 5

This is a way to purify proteins. The theory is that a selected protein is soluble in water only within a certain range of salt concentration. By adding salt to a homogenized solution, certain components are "salted out" meaning that they no longer are soluble in the solution and precipitate out. Often times it is known at what point a target protein will salt out so it is possible to isolate said protein by slowly increasing the concentration of the salt until you hit that range and the protein precipitates out of solution.

Answer 6

Salting out is a method of separating proteins based on the principle that proteins are less soluble at high salt concentrations. The salt concentration needed for the protein to precipitate out of the solution differs from protein to protein. This process is also used to concentrate dilute solutions of proteins. Dialysis can be used to remove the salt if needed.

Answer 7

when mixture of water soluble compounds are present in water solution, highly water soluble comound will kick off , i.e. drive out less water soluble compounds i.e. salt out effect.

Answer 8

It simply implies 'evaporation'!