Sodium lauryl sulfate (
SLS) or
sodium dodecyl sulfate (
SDS or NaDS) (
C12H25SO4Na) is an
anionic surfactant that is used in industrial products including engine degreasers, floor cleaners, and car wash soaps; as well as 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, C
12H
25OH), 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 (CMC) 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, it 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.
See also
References
External links
