Salting out
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Salting out (also known as salt-induced precipitation, salt fractionation, anti-solvent crystallization, precipitation crystallization, or drowning out)
Principle
Salt compounds dissociate in aqueous solutions. This property is exploited in the process of salting out. When the salt concentration is increased, some of the water molecules are attracted by the salt ions, which decreases the number of water molecules available to interact with the charged part of the protein.[3]
There are
When salt is added to the solution, there is more frequent interaction between solvent molecules and salt ions. As a result, the protein and salt ions compete to interact with the solvent molecules with the result that there are fewer solvent molecules available for interaction with the protein molecules than before. The
Soaps are easily precipitated by concentrated salt solution, the metal ion in the salt reacts with the fatty acids forming back the soap and glycerin (glycerol). To separate glycerin from the soap, the pasty boiling mass is treated with brine (NaCl solution). Contents of the kettle salt out (separate) into an upper layer that is a curdy mass of impure soap and a lower layer that consists of an aqueous salt solution with the glycerin dissolved in it. The slightly alkaline salt solution, termed spent lye, is extracted from the bottom of the pan or kettle and may be subsequently treated for glycerin recovery.[citation needed]
Application
As different proteins have different compositions of amino acids, different protein molecules precipitate at different concentrations of salt solution.[citation needed]
Unwanted proteins can be removed from a protein solution mixture by salting out as long as the solubility of the protein in various concentrations of salt solution is known. After removing the precipitate by filtration or centrifugation, the desired protein can be precipitated by altering the salt concentration to the level at which the desired protein becomes insoluble.[6]
One demerit of salting out in purification of proteins is that, in addition to precipitating a specific protein of interest, contaminants are also precipitated as well. Thus to obtain a purer protein of interest, additional purification methods such as ion exchange chromatography may be required.[7]
See also
References
- ^ Genck, Wayne (2010). "Make The Most of Antisolvent Crystallization". Chemical Processing. PutmanMedia.
- .
- PMID 6525340.
- PMID 31501317.
- ISBN 978-0-444-63688-1.
- PMID 18429073.
- PMID 24674064.
Further reading
- Sheehan, David (2009). Physical Biochemistry: Principles and Applications. John Wiley & Sons. p. 285. ISBN 978-0-470-85602-4.
- Miller, S A; Dykes, D D; Polesky, H F (11 February 1988). "A simple salting out procedure for extracting DNA from human nucleated cells". Nucleic Acids Research. 16 (3): 1215. PMID 3344216.
- McKay, H. A. C. (1 January 1953). "Activities and activity coefficients in ternary systems". Transactions of the Faraday Society. 49: 237–242. .
External links
- Make The Most of Antisolvent Crystallization
- Salting out on UC Davis ChemWiki