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- 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.
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