Sodium dodecyl sulfate

Sodium dodecyl sulfate (SDS) or sodium lauryl sulfate (SLS), sometimes written sodium laurilsulfate, is an organic compound with the formula Template:Chem2 and structure Template:Chem2. It is an anionic surfactant used in many cleaning and hygiene products. This compound is the sodium salt of the 12-carbon organosulfate. Its hydrocarbon tail combined with a polar "headgroup" give the compound amphiphilic properties that make it useful as a detergent. SDS is also component of mixtures produced from inexpensive coconut and palm oils. SDS is a common component of many domestic cleaning, personal hygiene and cosmetic, pharmaceutical, and food products, as well as of industrial and commercial cleaning and product formulations.<ref name=UllmannSurf/>

Physicochemical properties

File:Sodium dodecyl sulfate.jpg

Bottle of 20% sodium dodecyl sulfate in distilled water for use in the laboratory

The critical micelle concentration (CMC) in water at 25 °C is 8.2 mM,<ref name=CMC /> and the aggregation number at this concentration is usually considered to be about 62.<ref>Template:Cite journal</ref> The micelle ionization fraction (α) is around 0.3 (or 30%).<ref name="Barney_L">Template:Cite journal</ref>

Applications

Cleaning and hygiene

SDS is mainly used in detergents for laundry with many cleaning applications.<ref name="Ullmann">Smulders, Eduard ; Rybinski, Wolfgang; Sung, Eric; Rähse, Wilfried; Steber, Josef; Wiebel, Frederike & Nordskog, Anette. (2002) "Laundry Detergents," in Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, Template:DoiTemplate:Page needed</ref> It is a highly effective surfactant and is used in any task requiring the removal of oily stains and residues. For example, it is found in higher concentrations with industrial products including engine degreasers, floor cleaners, and car exterior cleaners.Template:CN

It is a component in hand soap, toothpastes, shampoos, shaving creams, and bubble bath formulations, for its ability to create a foam (lather), for its surfactant properties, and in part for its thickening effect.<ref>Template:Cite web</ref>

Food additive

Sodium dodecyl sulfate, appearing as its synonym sodium lauryl sulfate (SLS), is considered a generally recognized as safe (GRAS) ingredient for food use according to the USFDA (21 CFR 172.822).<ref>Template:Cite web</ref> It is used as an emulsifying agent and whipping aid.<ref>Template:Cite bookTemplate:Page needed</ref> As an emulsifier in or with egg whites the United States Code of Federal Regulations require that it must not exceed 1,000 parts per million (0.1%) in egg white solids or 125 parts per million (0.0125%) in frozen or liquid egg whites and as a whipping agent for the preparation of marshmallows it must not exceed 0.5% of the weight of gelatine.<ref>Template:Cite web</ref> SLS is reported to temporarily diminish perception of sweetness.<ref>Template:Cite book</ref>

Laboratory applications

SDS is used in cleaning procedures,<ref>Template:Cite web</ref> and is commonly used as a component for lysing cells during RNA extraction or DNA extraction, inhibiting the activity of nucleases, enzymes that can degrade DNA, protecting the integrity of the isolated genetic material, and for denaturing proteins in preparation for electrophoresis in the SDS-PAGE technique.<ref>The acronym expands to "sodium dodecyl sulfate-polyacrylamide gel electrophoresis."</ref>

File:Protein-SDS interaction.png

Denaturation of a protein using SDS

In the case of SDS-PAGE, the compound works by disrupting non-covalent bonds in the proteins, and so denaturing them, i.e. causing the protein molecules to lose their native conformations and shapes. By binding to proteins at a ratio of one SDS molecule per 2 amino acid residues, the negatively charged detergent provides all proteins with a similar net negative charge and therefore a similar charge-to-mass ratio.<ref name=":2">Template:Cite book</ref> In this way, the difference in mobility of the polypeptide chains in the gel can be attributed solely to their length as opposed to both their native charge and shape.<ref name=":2" /><ref>Template:Cite book</ref> This separation based on the size of the polypeptide chain simplifies the analysis of protein molecules.<ref name=":0">Template:Cite book</ref>

Pharmaceutical applications

Sodium lauryl sulfate is a widely used in the pharmaceutical field as an ionic solubilizer and emulsifier that is suitable for applications in liquid dispersions, solutions, emulsions and micro emulsions, tablets, foams and semi-solids such as creams, lotions and gels.<ref>Template:Cite web</ref> Additionally, SLS aids in tablet wettability, as well as lubrication during manufacturing. Brand names of pharma-grade SLS include Kolliphor SLS and Kolliphor SLS Fine.<ref>Template:Cite web</ref>

Miscellaneous applications

SLS is used in an improved technique for preparing brain tissues for study by optical microscopy. The technique, which has been branded as CLARITY, was the work of Karl Deisseroth and coworkers at Stanford University, and involves infusion of the organ with an acrylamide solution to bind the macromolecules of the organ (proteins, nucleic acids, etc.), followed by thermal polymerization to form a "brain–hydrogel" (a mesh interspersed throughout the tissue to fix the macromolecules and other structures in space), and then by lipid removal using SDS to eliminate light scattering with minimal protein loss, rendering the tissue quasi-transparent.<ref name=ShenNatureNews2013>Template:Cite journalTemplate:Better source</ref><ref name=ChungDeisserothNature2013>Template:Cite journal</ref>

Along with sodium dodecylbenzene sulfonate and Triton X-100, aqueous solutions of SDS are popular for dispersing or suspending nanotubes, such as carbon nanotubes.<ref>Template:Cite journal</ref>

Other uses

SLS has been proposed as a potentially effective topical microbicide, for intravaginal use, to inhibit and possibly prevent infection by various enveloped and non-enveloped viruses such as the herpes simplex viruses, HIV, and the Semliki Forest virus.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>

Liquid membranes formed from SDS in water have been demonstrated to work as unusual particle separators.<ref>Template:Cite journal</ref> The device acts as a reverse filter, allowing large particles to pass while capturing smaller particles.

Production

Dodecyl alcohol is sulfated using sulfur trioxide. The reaction proceeds by initial formation of the pyrosulfate:

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Several million tons are produced annually.<ref name=UllmannSurf>Template:Cite book</ref>

SDS can also be synthesized by treating lauryl alcohol with chlorosulfuric acid.<ref>Template:Cite journal</ref> The resulting half ester of sulfuric acid is then neutralized with alkali.

Lauryl alcohol can be used in pure form or as a mixtures of fatty alcohols. When produced from these sources, "SDS" products are a mixture of various sodium alkyl sulfates with SDS being the main component.<ref>Template:Cite bookTemplate:Page needed</ref> For instance, SDS is a component, along with other chain-length amphiphiles, when produced from coconut oil, and is known as sodium coco sulfate (SCS).<ref>Template:Cite patent</ref> SDS is available commercially in powder, pellet, and other forms (each differing in rates of dissolution), as well as in aqueous solutions of varying concentrations.Template:Citation needed

Safety

SDS is not carcinogenic in low concentrations according to someTemplate:Clarify studies.<ref name="Final_Report_SLS">Template:Cite journal.</ref><ref name="Final_Report_CIR2005">Template:Cite journal.</ref> Like all detergents, sodium lauryl sulfate removes oils from the skin, and can cause skin and eye irritation.Template:Citation needed It has been shown to irritate the skin of the face, with prolonged and constant exposure (more than an hour) in young adults.<ref name="Marrakchi_S">Template:Cite journal</ref> SDS may worsen skin problems in individuals with chronic skin hypersensitivity, with some people being affected more than others.<ref name="Agner_T">Template:Cite journal</ref><ref name="A._Nassif_1994">Template:Cite journal</ref><ref name="Loffler_H">Template:Cite journal</ref>

Oral concerns

SDS is a common ingredient in toothpastes due to its low cost,<ref name = LippertvanLoveren13>Template:Cite book</ref> its lack of impact on taste,<ref name = LippertvanLoveren13/> and its desirable action as a foaming agent.<ref name = LippertvanLoveren13/>

VSCs

SDS may reduce the amount of bad breath-causing volatile sulfur compounds (VSCs) in the mouth.<ref name = DadamiovanLoveren13>Template:Cite book</ref> A series of small crossover studies (25–34 patients) have supported the efficacy of SLS in the reduction of VSCs, and its related positive impact on breath malodor, although these studies have been generally noted to reflect technical challenges in the control of study design variables.<ref name = DadamiovanLoveren13/>

Dry mouth

Primary sources from the group of Irma Rantanen at University of Turku, Finland claim that SLS-containing pastes cause more dry mouth (xerostomia) than their proposed alternative. However, a 2011 Cochrane review of these studies, and of the more general area, concludes that there "is no strong evidence... that any topical therapy is effective for relieving the symptom of dry mouth."<ref>See Template:Cite journal See Rantanen, et al. (2003) J. Contemp. Dent. Pract. 4(2):11–23, [1], and Rantanen, et al. (2003) Swed. Dent. J. 27(1):31–34, [2], referenced therein.</ref>

Mouth ulceration

A safety concern has been raised on the basis of several studies regarding the effect of toothpaste SDS on aphthous ulcers (more specifically, mouth ulcers or "canker sores"), commonly referred to as canker or white sores.<ref name = LippertvanLoveren13/> According to the NHS and Alessandro Villa of the Miami Cancer Institute, SLS is a cause for concern for mouth ulcers.<ref name="k527">Template:Cite web</ref><ref>Template:Cite web</ref><ref>Some of the published studies, from latest to earliest, are as follows. (i) A 2012 double-blind crossover study of 90-patients failed to find a significant difference in number of ulcers between groups using SLS-containing toothpaste, versus a group using an SLS-free toothpaste, but did suggest significant reduction in ulcer duration and improvement in patient pain scores, see Template:Cite journal, a study also cited in the Lippert (2013) book chapter. (ii) A 1999 double-blind crossover study of 47 patients failed to find any statistically significant difference in the number, episodes, and duration of such ulcers between these two groups, and of pain scores between them, see Template:Cite journal (iii) A 1997 study suggested a significantly higher number of ulcers after SLS toothpaste use, versus its control group, see Template:Cite journal, a study also cited in the Lippert (2013) book chapter. (iv) A 1996 follow-up 30-patient double-blind crossover study and a 1994 preliminary 10-patient crossover study by the same authors suggested significantly higher numbers of aphthous ulcers after using SLS-containing toothpaste, compared with an SLS-free toothpaste, see Template:Cite journal and Template:Cite journal</ref> As Lippert notes, of 2013, "very few... marketed toothpastes contain a surfactant other than SLS [SDS]," and leading manufacturers continue to formulate their produce with SDS.<ref name = LippertvanLoveren13/> According to Allesandro Villa of the Miami Cancer Institute, one theory is that SLS disrupts the protective layer of mucus covering the mouth.<ref name="k527"/>

See also

• Sodium tetradecyl sulfate, another anionic surfactant in common use
• Mouth ulcer

External links

• Josh Clark, "Why does orange juice taste bad after you brush your teeth?"
• Template:YouTube published on Aug 24, 2018 Science (journal)