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.

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. 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.
 * 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".
 * 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. Furthermore, the Environmental Working Group has claimed in their Skin Deep Report that SLS is a penetration enhancer.

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%).
 * The Optical refractive index increment of a pure aqueous solution at wavelength 532 nm is about 0.1070 ml/g.