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Detergents

Detergents - also termed as tensides or surfactants - are amphipathic compounds with both lipophilic (hydrophobic; non-polar) and hydrophilic (polar) sides within one molecule.

Therefore they are soluble in aqueous solution as well as in non-polar organic solvents - and they are able to influence the solubility of other molecules (like lipids or hydrophobic proteins in buffer solutions). Detergents are widely used in biochemistry, cell biology or molecular biology. Cell lysis, protein solubilization, protein crystallization or reduction of background staining in blotting experiments are just a few examples.

Detergents can be classified for instance according to their chemical structure stating their constituent polar and nonpolar group (glucosides, alkyl ionic detergents, polyoxyethylene alcohols, bile salts, sulphonates etc.), the charge character (anionic, cationic, zwitterionic = amphoteric; non-ionic) or simply whether they are mild or strong in terms of their ability to solubilize and / or to denature proteins. We decided to arrange our detergents according to their charge:

  • anionic detergents
  • cationic detergents
  • zwitterionic detergents
  • non-ionic detergents
  • isomeric pure detergents for crystallography

But how to choose the right detergent?

There is a large number of different detergents available and choosing the best detergent for a special application is not trivial. In many cases, a set of detergents has to be tested to select the one with the best properties. If the goal is the isolation of a protein preserving its structural and functional state, one should consider the temperature, the pH and the ionic strength of the system as well as interference with assays. Several other parameters may influence the choice too. Assuming that the factors mentioned above are dictated by the protein and are held constant, the factors that are left to be optimised are the detergent's strength (in this case a mild, non-denaturating one), chemical structure, solubility and concentration.

The CMC value is specific to each detergent

Above a critical concentration, called CMC value (Critical Micellar Concentration), detergents start forming stable aggregates (micelles). The CMC value is specific to each detergent and different factors (chemical structure, pH value, temperature, ionic strenth) may influence it. In aqueous solutions, the hydrophilic site of the monomers will be on the outside of the micelle, and the lipohilic portion inside. In organic solvents, reversed micelles form, with the lipophilic site outside. The micelle size increases and the CMC decreases with increasing size of the lipophilic part of the detergent and, to a lesser extent, with decreasing size and polarity of the polar groups. That means, that detergents with a higher hydrophilic part are characterized by a higher CMC (start to form micelles at higher concentrations) and smaller micelles than higly lipophilic detergent. Above the CMC, free monomer molecules are in equilibrium with the micelles and the solubilizing ability increases. Detergents with high CMC values are more easily removed by dialysis.

More detailed informationen about detergents is provided in our brochure "Detergents"; including criteria for selection, hints for isolation, solubilisation and reconstitution of membrane proteins, references and more.

Overview Detergents

anionic detergents
Prod. No. Description M [g/mol] CMC (25°C) Comment
A1013 1-Pentanesulfonic acid sodium salt monohydrate 192.21
A7402 N-Lauroylsarcosine sodium salt 293.39 13.7 mM High solubility in chaotrope high salt solutions (in contrast to SDS) and therefore first choice for applications in guanidinium-containing lysis buffers: Addition to cell or tissue homogenates improves the purity of RNA isolated by the guanidine hydrochloride method.
Laurylsarcosine releases chromatin from all proteins and increases the activity of RNA polymerase II (probably by improved access of the polymerase to the template).
We also provide laurylsarcosinate solutions and different qualities, e.g. ultrapure A1163
A0979 Sodium cholate 430.57 10 mM Water soluble bile salt; component of different lysis buffers (e.g. RIPA). Further applications are liposome preparations, isolation of membrane proteins or lipids, affinity chromatography and cell culture. Sodium cholate should not be used for ion-pairing exchange chromatography or electrophoresis, and when working with enzymes, that need bivalent cations for their activity. It does not interfere with protein assays and can easily be dialysed.
A1531 Sodium deoxycholate 414.57 2.7 mM (20°C) See A0979
A2572 SDS (sodium dodecylsulfate) 288.38 8.2 mM The main field of application is polyacrylamide electrophoresis; SDS binds almost all water soluble proteins (~1,4 g SDS / g protein) and enables protein separation by size (without considering the native charge or tertiary structure). Further application is in blotting and cell lysis. We offer SDS in different qualities and as solution (20- or 10% SDS, A0676).
cationic detergents
Prod. No. Description M [g/mol] CMC (25°C) Comment
A0805 Cetyltrimethylammonium bromide (CTAB) 364.46 0.92 mM Used in polyacrylamide gel electrophoresis for proteins, which show an unusual migration behavior in the SDS-PAGE (e. g. strongly charged proteins or subunits of membrane proteins).
Another important application of CTAB is the precipitation of high molecular weight DNA, especially from plant material. For this application we suggest to use CTAB molecular biology grade, A6284
zwitterionic detergents
Prod. No. Description M [g/mol] CMC (25°C) Comment
A1099 CHAPS 614.89 6.5 mM Cholate derivative; suitable for experiments that require functional proteins in their native state. No interference with protein assays according to Lowry. Easy to remove by dialysis.
non-ionic detergents
Prod. No. Description M [g/mol] CMC (25°C) Comment
A1381 1198.56 0.09 mM Mild detergent with a polyoxyethylen head group. As a rule, these detergents do not denature proteins, making them a useful tool in studying proteins in their native state. Proteins, that are composed of several subunits will not dissociate.
Brij® 35 This product is also available as a 10% solution (peroxide-free): A1286
A1669 Brij® 58 1123.51 0.077 mM Incubation of living cells with this detergent produces the so-called cytoskeleton. Proteins leak from the cells after a lag phase, depending on the detergent concentration, time of exposure and cell type. Enzyme activity may be determined in the presence of Brij® 58.
A1905 Digitonin 1229.34 Steroid glycoside from Digitalis purpurea; permeabilize plasma membranes (this capability may differ from batch to batch from all suppliers!) and form complexes with cholesterol. Frequently used to dissolve membrane-bound proteins. Digitonin is hardly soluble in either water, chloroform or ether. You may dissolve it in absolute ethanol or DMSO.
A1386 MEGA-8 321.42 58 mM N-D-Gluco-N-methylalkanamide; chemical analoga of alkyl glucoside. Easily removable by dialysis. No absorbance at 280 nm (in contrast to NP40 and Triton® X-100). Compatible with ion pair chromatography and numerous buffers. During solubilisation of membranes, the embedded proteins are not denaturated, but protein-protein-interactions are released.
Purity > 99 %; free of alpha-isomer.
A1694 Nonidet® P40 (Substitute) 0.34 mM Suitable for isolation of core proteins and cytoplasmatic proteins from eukaryotic cells (RIPA lysis buffer). Affects the protein-DNA bound; caution in electrophoretic mobility shift assays!
Adding NP40 into the sequencing reaction of linear or "supercoiled" plasmid DNA increases the quality and avoids additional alkaline denaturation. This product is also available as a 10% solution (peroxide-free): A2239
A1288 Pluronic® F-68 ˜8350 Copolymers from ethylene- (approx. 80 %) and propylene oxide. Pluronic F-68 is applied in the culturing of mammalian cells in large batches. It prevents the sticking of air bubbles to cells, which develop during mixing within the fermentor, stabilizes the foam on the surface or improves the resistance of the cell membrane against hydrodynamic shearing.
A4518 Saponin from Quillaja Bark Mixture of terpenoid molecules and glycosides. Permeabilizes the cell membrane by interaction with the cholesterol present in the cell membrane. Thereby large pores form; enabling the entry of conjugated antibodies. Saponin has become the detergent of choice for cytokine staining and phospho-epitope staining protocols.
A3848 Triton® X-114 558.75 0.35 mM Triton® X-114 forms a clear, micellar solution at low temperatures. Above 20°C, two phases are formed by aggregation of micells. Extraction of cellular material for the isolation of proteins is performed at low temperatures.
A4974 Tween® 20 1227.72 0.059 mM Polysorbat 20; common component in immunoassay-buffers; interferes with protein determination according to Bradford.
Also available in other qualities and as a 10% solution (peroxide-free):
A1284
A1390 Tween® 80 1310 0.01 mM Polysorbat 80
Isomeric pure alkyl-β-D-glucosides for isolation und Crystallisation of membrane proteins
Prod. No. Description M [g/mol] CMC (25°C) Comment
A1010 n-Octyl-β-D-glucopyranoside 292.38 25-30 mM One of the frequently used detergents in membrane research: Non-denaturating (allows isolation of functional proteins); Highly water soluble and easily removable by dialysis. No absorbance at 280 nm.
(n=7) Purity > 99 %; free of alpha-isomer.
A1145 n-Octyl-β-D-thioglucopyranoside 308.44 9 mM Alternative to octylglucoside. More stable in solution than octylglucoside; not cleavable by β-Glucosidases.
Purity > 99 %; free of alpha-isomer.
Isomeric pure alkyl-β-D-maltosides for isolation and Crystallisation of membrane proteins
A6769 n-Decyl-β-D-maltoside 482.57 1.8 mM Purity > 99,5 %; free of alpha-isomer.
(n=9)
A0819 n-Dodecyl-β-D-maltoside 510.63 0.15 -0.19 mM Lauryl maltoside; primarily developed for isolation of the mitochondrial cytochrom c oxidase.
(n=11) Purity > 99 %; free of alpha-isomer. Also available in "Crystallography grade" (Purity > 99.5 %): A6817


Trademarks:
Brij (Atlas Chemicals Co.)
Nonidet (Shell)
Triton (Union Varbide Co.)
Pluronic, Tween (ICI America Inc.)

General properties of the main classes of detergents

Ionic detergents contain a negatively (anionic detergent) or positively (cationic detergent) charged hydrophilic head group. The hydrophobic part is either an alkyl chain (as for SDS, CTAB or alkyl sulfonic acids) or a more complicated steroidal structure as a bile acid salt (like cholate and deoxycholate). The latters are more rigid in their structure and carry additional hydrophilic groups (hydroxyl groups) within the hydrophobic steroide scaffold. Thus, bile salts only show a polar and an apolar face, not a well-defined polar head group.
The size of the micelles is affected by repulsion forces between the charged polar groups and hydrophobic attraction between the side chains. As a result, the micellar size of ionic detergents can be manipulated by the ion strength. Increasing the concentration of neutralizing counter ions leads to a larger micelle size. At the same time, the increased ion strength results in a lower CMC. Changing the temperature on the other hand only slightly influences the CMC. Ionic detergents generally have higher CMC values than their non-ionic analoga.
Alkyl-ionic detergents mostly act denaturating and separate protein complexes into their subunits.

Non-ionic detergents possess an uncharged, hydrophilic head group consisting of either polyoxyethylene units (e.g. Brij® und Triton®) or sugars (alkyl glucosides or maltosides). The CMC value and micellar size of this detergent group is mainly affected by temperature (the higher the temperature the higher the CMC), not by ion strength.
Non-ionic detergents generally are non-denaturating and therefore first choice for applications that require preservation of protein structure and activity. They are mild detergents that primarily break lipid-lipid and lipid-protein interactions, while protein-protein interactions stay unaffected. Especially alkyl glycosides and maltosides are suitable for isolation of biological active membrane proteins; advantages over polyoxyethylene detergents are e.g. homogenity in composition and structure (many polyoxyethylenes are composed of several homologs) und a lack of absorbance at 280 nm (detergents containing aromatic rings absorb in the ultraviolet region and may interfere with spectrophotometric monitoring of proteins at 280 nm).

Zwitterionic detergents, like CHAPS or sulfobetaine, combine the features of ionic and non-ionic detergents. Like non-ionic detergents they have no net charge. Consequently they show no electrophoretic mobility and do not bind to ion-exchange resins. Compared to ionic detergents, their CMC values are less sensitive to changes in ion concentration, but they have in common to break protein-protein interactions efficiently (denaturating effect).