The sodium dodecyl sulfate (SDS), is an anionic, synthetic and amphiphilic organic salt. The apolar and hydrophobic part corresponds to the hydrocarbon chain; while the polar and hydrophilic part is due to sulfate, with a negative charge.
SDS is a surfactant: its molecules are placed on the surface of aqueous solutions, producing a decrease in surface tension. This feature allows it to be used in shampoo, toothpastes, soaps and other personal care and household cleaning items..
Sodium dodecyl sulfate binds to the protein and produces its unfolding, acquiring an elongated shape. The sulfate groups are exposed to water, acquiring negative charges, the number of which is proportional to their molecular weight..
For this reason the SDS allows the determination of the molecular weights of proteins by polyacrylamide electrophoresis..
Although a possible carcinogenic effect of SDS has been suspected, it has not been conclusively shown to be so. SDS can cause skin and eye irritation like other detergents..
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In the first image, the SDS molecule was shown with a spheres and rods model. As can be seen, it has a hydrophobic and nonpolar carbonated tail (black and white spheres); and at the same time, a polar head, thanks to the presence of the group -SO4- (yellow and red spheres).
Although not shown, there should be a purple sphere representing the Na cation.+, right next to the -SO group4-, interacting electrostatically.
That said, it is easy to see why this compound is amphiphilic; and also an anionic surfactant, since the charge of SDS is negative and can attract other cations in addition to Na+.
The molecule gives the false impression of being rigid, an immovable linear structure. However, it is just the opposite. The SDS could be compared to a "worm", whose carbonated tail exhibits multiple vibrations and rotations of its single bonds. This makes it capable of adopting different shapes or folds in the middle; in water, for example.
Although it is true that sodium dodecyl sulfate is a dynamic molecule, in the solid state it does not need to move too much, behaving like a "simple" rod. And thus, each molecule or bar is positioned in such a way as to increase the interactions between the carbonate tails and, at the same time, those of their ionic charges..
The result is the formation of a monoclinic crystal, where the SDS molecules are packed into several columns of bars (top image). The intermolecular forces that bind them are such that these crystals require a temperature of 206ºC to melt into the liquid phase..
Outside the comfort of its crystals, the SDS molecule can no longer sit still; begins to twist its tail to increase or decrease interactions with the outside environment.
If this medium is water, a phenomenon called micelle formation occurs: the carbonated and hydrophobic tails join to arm each other, while the polar heads, the -SO groups4-, remain on the surface interacting with H moleculestwoOR.
The micelle then takes on an oblate ellipsoid morphology (like Earth, but more squashed). In glass they are as blocks of bars, and in aqueous medium as ellipsoid micelles. What if the medium was oily? The micelle would be reversed: the polar heads SO4- would go to the core, while their carbonated tails would be exposed to the oil.
- Sodium dodecyl sulfate (SDS).
- Sodium lauryl sulfate (SLS).
C12H25OR4SNa.
288.378 g / mol.
Various presentations: dry powder, liquid or wet solid. Its crystals have a white or creamy color.
Faint odor of fatty substances, odorless.
206 ºC.
1 105 mg / L. 1 g dissolved in 10 mL of an opalescent solution.
1.01 g / cm3.
Stable under recommended storage conditions.
When heated to decomposition it emits a white smoke of sulfur oxide and sodium oxide.
39.5 dynes / cm at 25 ° C.
It is 8.2 mM in pure water at 25 ºC.
Dodecyl sulfate is a surfactant that is used in many products, such as hand soaps, foam baths, shaving creams, etc. It is also used to remove hard-to-remove stains from clothes, cleaning floors and bathrooms, scrubbing kitchen items, etc..
It is used as a repellent for fleas and ticks, present in animals. It is also used as a humectant in some antibiotics, for oral or topical use..
SDS is microbicidal against enveloped viruses, such as HIV, types 1 and 2, and the herpes simplex virus (HSV-2). It also acts on non-enveloped viruses: papillomavirus, reovirus, rotavirus, and poliovirus. However, this use is not approved..
The use of SDS has been suggested as a douche to provide protection against sexually transmitted viruses. Also, in the processing of breast milk to eliminate or reduce the possibility of HIV transmission via breastfeeding.
In addition to its antiviral action, SDS acts on pathogenic bacteria and fungi. SDS removes drug resistance and sex transfer factors from E. coli; and blocks the growth of numerous Gram positive bacteria.
SDS binds to proteins causing their denaturation, supplying them with negative charges and a conformational change. This allows the determination of their molecular weights by polyacrylamide electrophoresis..
SDS is also used in the preparation of brain tissue samples for use in light microscopy. It is also used in the preparation of blood samples for counting the number of erythrocytes..
SDS is used in the purification of nucleic acids, due to its ability to dissolve membranes and its inhibitory action on the activity of RNase and DNase enzymes..
In addition, SDS is used in the characterization of quaternary ammonium compounds..
SDS is used as an emulsifier and thickener in foods. Improves the stability and texture of baked goods. Additionally, it is used as an auxiliary in beating dry egg products..
SDS is used in the electroplating industry, particularly nickel and zinc; as an emulsifier and penetrant in varnish and paint remover; in the formulation of injection molded explosives; and in solid rocket propellants as foaming agent.
Constant exposure to SDS can cause skin hyperplasia in guinea pigs. Rabbits and humans are less susceptible to these injuries. Direct contact with SDS at a concentration ≤ 20%, can cause moderate inflammation and skin irritation.
On the other hand, prolonged exposure to SDS can cause dermatitis, with signs of redness, swelling and blistering..
SDS can cause eye irritation on contact. It can also be very reactive in some people, causing irritation of the respiratory tract and respiratory distress by inhalation..
In rare cases, ingestion of SDS can cause caustic injury. But, it has been reported in children who have ingested SDS, rapidly developing profuse vomiting, CNS depression and respiratory distress..
No evidence of genotoxicity or teratogenic action has been found in SDS. In 242 patients with eczematous dermatitis, 6.4% of the patients were found to have an allergy, attributable to the use of the SDS.
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