Sodium dodecyl sulfate
Overview
Sodium dodecyl sulfate (or sulphate) (SDS or NaDS) (C12H25NaO4S), also known as sodium lauryl sulfate (SLS), is an anionic surfactant that is used in household products such as toothpastes, shampoos, shaving foams and bubble baths for its thickening effect and its ability to create a lather. The molecule has a tail of 12 carbon atoms, attached to a sulfate group, giving the molecule the amphiphilic properties required of a detergent.
It is prepared by sulfonation of dodecanol (lauryl alcohol, C12H25OH) followed by neutralization 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.
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.[1]
Biochemical applications
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.
Safety concerns relating to SDS
A number of safety concerns about SDS have been raised in published reports.[2][3][4] These include claims that:
- SDS causes a number of skin issues (for which the non-specific term is dermatitis), with some people being affected more than others.[4][5][6]
- Although SLES is slightly less irritating than SDS, the liver is unable to metabolize SLES.
- SDS causes aphthous ulcers, commonly referred to in some countries as "canker sores".[7][8]
- SDS may be used in place of the less irritant SLES in many soaps, shampoos, washing powders, toothpastes and other bathroom products because of its lower cost.
The American Cancer Society denied that SDS is carcinogenic, and points out that the substance, while undoubtedly a skin irritant, is dangerous only at higher concentrations than those used in cosmetics.[9] Furthermore, the Environmental Working Group has claimed in their Skin Deep Report that SLS is a penetration enhancer.[10]
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 50. The micelle ionization fraction (α) is around 0.3 (or 30%).[11]
- The Optical refractive index increment of a pure aqueous solution at wavelength 532 nm is about 0.1070 ml/g.
See also
References
- ↑ Kazuyoshi Watanabe, Shuntaro Imai and Yasuhiko H. Mori. Surfactant effects on hydrate formation in an unstirred gas/liquid system: An experimental study using HFC-32 and sodium dodecyl sulfate. Department of Mechanical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522. Japan.Chemical Engineering Science. Volume 60, Issue 17, September 2005, Pages 4846-4857. Abstract
- ↑ Agner T. Susceptibility of atopic dermatitis patients to irritant dermatitis caused by sodium lauryl sulphate. Acta Derm Venereol. 1991;71(4):296-300. PMID 1681644
- ↑ A. Nassif, S. C. Chan, F. J. Storrs and J. M. Hanifin. Abstract: Abnormal skin irritancy in atopic dermatitis and in atopy without dermatitis. Arch Dermatol. November 1994;130(11):1402. Abstract
- ↑ 4.0 4.1 Marrakchi S, Maibach HI. Sodium lauryl sulfate-induced irritation in the human face: regional and age-related differences. Skin Pharmacol Physiol. 2006;19(3):177-80. Epub 2006 May 4. PMID 16679819
- ↑ 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.
- ↑ Loffler H, Effendy I. Skin susceptibility of atopic individuals. Department of Dermatology, University of Marburg, Germany. Contact Dermatitis. 1999 May;40(5):239-42. PMID 10344477
- ↑ Chahine L, Sempson N, Wagoner C. The effect of sodium lauryl sulfate on recurrent aphthous ulcers: a clinical study. Compend Contin Educ Dent. 1997 Dec;18(12):1238-40. PMID 9656847
- ↑ Herlofson BB, Barkvoll P. The effect of two toothpaste detergents on the frequency of recurrent aphthous ulcers. Acta Odontol Scand. 1996 Jun;54(3):150-3. PMID 8811135
- ↑ Debunking the Myth. American Cancer Society. 1998/09/23. Article
- ↑ Skin Deep Report. Environmental Working Group. Revised October 1995. SLS Rating
- ↑ Barney L. Bales, Luis Messina, Arwen Vidal, Miroslav Peric, and Otaciro Rangel Nascimento. Precision Relative Aggregation Number Determinations of SDS Micelles Using a Spin Probe. A Model of Micelle Surface Hydration. J. Phys. Chem. B. 1998 102(50)10347-10358. Abstract
External links
- Sodium Lauryl Sulfate: chemical data sheet from chemicalland21.com
- Tom of Maine's FAQ: Is sodium lauryl sulfate (SLS) safe for use?
- Urban Legends Reference Pages: Shampoo Sham, snopes.com
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