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Sodium lauryl sulfate (SLS), sodium laurilsulfate or sodium dodecyl sulfate (SDS or NaDS) (C12H25SO4Na) is an anionic surfactant used in many cleaning and hygiene products. The molecule has a tail of 12 carbon atoms, attached to a sulfate group, giving the molecule the amphiphilic properties required of a detergent.
SLS is a highly effective surfactant and is used in any task requiring the removal of oily stains and residues. As such the compound is found in high concentrations in industrial products including engine degreasers, floor cleaners, and car wash soaps. In household products, SLS is used in lower concentrations with toothpastes, shampoos, and shaving foams. It is an important component in bubble bath formulations for its thickening effect and its ability to create a lather.
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.
The product can also be used to aid in lysing cells during DNA extraction and for unraveling proteins in SDS-PAGE (see below).
In medicine, sodium laurilsulfate is used rectally as a laxative in enemas, and as an excipient on some dissolvable aspirins and other fiber therapy caplets.
Sodium lauryl sulfate, in science referred to as sodium dodecyl sulfate (SDS), is commonly used in preparing proteins for electrophoresis in the SDS-PAGE technique. This compound works by disrupting non-covalent bonds in the proteins, denaturing them, and 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. Sodium lauryl sulfate is probably the most researched anionic surfactant compound. Like all detergent surfactants (including soaps), sodium lauryl sulfate removes oils from the skin, and can cause skin and eye irritation. The critical micelle concentration (CMC) in pure water at 25°C is 0.0082 M, and the aggregation number at this concentration is usually considered to be about 62. The micelle ionization fraction (α) is around 0.3 (or 30%).
SLS is synthesized by reacting lauryl alcohol with sulfuric acid to produce hydrogen lauryl sulfate which is then neutralized through the addition of sodium carbonate. Lauryl alcohol is in turn usually derived from either coconut or palm kernel oil by hydrolysis, which liberates their fatty acids, followed by reduction of the acid group to an alcohol.
The actual structure of SLS: CnH2n+1SO4Na
Due to this synthesis method, SLS is actually not pure dodecyl sulfate but a mixture of alkyl sulfates with dodecyl sulfate as the main component.
Health and safety
SLS has not been proven to be carcinogenic when either applied directly to skin or consumed. SLS however is a strong surfactant and a number of health concerns have been raised in published reports.
- SLS may worsen skin problems in individuals with chronic skin hypersensitivity, with some people being affected more than others.
- SLS in toothpaste may cause aphthous ulcers, commonly referred to in some countries as canker sores. Using SLS free toothpaste may reduce the sores.
- SLS has also been shown to irritate the skin of the face with prolonged and constant exposure (more than an hour) in young adults. In animal studies SLS appears to cause skin and eye irritation.
Research suggests that SLS could represent a potential effective microbicide, which can also inhibit and possibly prevent infection by various enveloped and non-enveloped viruses such as the Herpes simplex viruses, HIV, and the Semliki Forest Virus.
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- ^ The acronym expands to "sodium dodecyl sulfate-polyacrylamide gel electrophoresis.
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- ^ SODIUM LAURYL SULFATE, Chemical Land21, http://chemicalland21.com/specialtychem/perchem/SODIUM%20LAURYL%20SULFATE.htm
- ^ European Pharmacopoeia: Sodium laurilsulfate
- ^ CIR publication. Final Report on the Safety Assessment of Sodium Lauryl Sulfate and Ammonium Lauryl Sulfate. Journal of the American College of Toxicology. 1983 Vol. 2 (No. 7) pages 127-181.
- ^ a b NICNAS
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