Sodium lauryl sulfate

Overview
Sodium lauryl sulfate (SLS) or sodium dodecyl sulfate (SDS or NaDS) (C12H25SO4Na) is an anionic surfactant that is used in household products such as toothpastes, shampoos, shaving foams, some dissolvable aspirins, fiber therapy caplets, 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.

Preparation
Sodium lauryl sulfate is prepared by esterification of sulfuric acid with dodecanol (lauryl alcohol, C12H25OH), followed by neutralization with sodium carbonate. It is used in both industrially produced and home-made cosmetics.

Applications
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 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%).

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.

SDS-PAGE
Sodium lauryl sulfate 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 SLS bind to the main peptide chain at a ratio of one SLS 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 SLS/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 SLS causes proteins to unfold into a rod-like shape thereby eliminating differences in shape as a factor for separation in the gel.

Reactions
SLS can be converted by ethoxylation to sodium laureth sulfate (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.

Safety
When handling SLS in its solid form use extreme caution, the compound easily particalizes into the air. If inhaled can cause a serious choking hazard.

A number of health concerns about SLS have been raised in published reports. These studies indicate that:


 * SLS may cause a number of skin problems (for which the non-specific term is dermatitis), with some people being affected more than others.
 * SLS in toothpaste may cause aphthous ulcers, commonly referred to in some countries as "canker sores". However, some studies find no connection between SLS in toothpaste and mouth ulcers.