Sodium dodecyl sulfate
Encyclopedia : S : SO : SOD : Sodium dodecyl sulfate
It is prepared by sulphation of 1-dodecanol (lauryl alcohol, CH3(CH2)10CH2OH) followed by neutralisation with sodium carbonate. It is used in both industrially produced and home-made cosmetics.
Like all detergent surfactants (including soaps), it removes oils from the skin, and can cause skin irritation. It is also irritating to the eyes.
SDS can be converted by ethoxylation to sodium laureth sulfate (also called sodium lauryl ether sulfate; SLES), which is less harsh on the skin, probably because it is not as much of a protein denaturant as is the unethoxylated substance.
It is probably the most researched anionic surfactant compound.
In laboratories, SDS is commonly used in preparing proteins for polyacrylamide gel electrophoresis (SDS-PAGE). SDS works by disrupting non-covalent bonds in the proteins, thereby denaturing them, causing the molecules to lose their native shape (conformation). Also, anions of SDS bind to the main peptide chain at a ratio of one SDS anion for every two amino acid residues. This effectively imparts a negative charge on the protein that is proportional to the mass of that protein (about 1.4 g SDS/g protein). This new negative charge is significantly greater than the original charge of that protein. The electrostatic repulsion that is created by binding of SDS causes proteins to unfold into a rod-like shape thereby eliminating differences in shape as a factor for separation in the gel.
It has recently found application as a surfactant in gas hydrate or methane hydrate formation reactions, increasing the rate of formation as much as 700 times.
Safety concerns relating to SLS
It would appear that we have two quite differing views [link] on the safety of using and exposing the body to constant low levels of toxic chemicals such as Sodium Lauryl Sulphate (SLS).
Different people are affected by SLS, and its derivatives, more than others. [link] It is suspected that SLS is linked [link] to a number of skin issues (dermatitis), and when combined [link] with certain chemicals, SLS may become a carcinogen.
SLS is commonly used in research laboratories [link] as the standard ingredient (with which other substances are compared) for irritating the skin.
There are over 150 different names [link] by which SLS and its derivatives are known.
Although SLES is slightly less irritating than SLS, the liver [link] is unable to metabolize SLES.
The prime reason SLS is used in many soaps, shampoos, washing powerders, toothpastes and other bathroom products, is to do with cost [link]. SLS is inexpensive.
Data
- The critical micelle concentration in pure water at 25°C is 0.0082 M, and the aggregation number at this concentration is usually considered to be about 64. The micelle ionization fraction (α) is around 0.3 (or 30%).
- The Optical refractive index increment of pure a aqueous solution at wavelength 532 nm is about 0.1070 ml/g.
- MP: 206°C
References
- [Sodium Lauryl Sulfate] from chemicalland21.com
- [Is sodium lauryl sulfate (SLS) safe for use?], Tom's of Maine Frequently Asked Questions
- [Urban Legends Reference Pages: Shampoo Sham]
- [Sodium Lauryl Sulfate in Shampoos], from a maker of products which avoid it
- [Sodium Lauryl Sulphate (SLS) Sorting the Facts from the Fiction]
- [Effects of sodium laurl-sulfate, avoid, SLS]
- [Green People - Sodium Laurel Sulphate]
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