Detergent Function & Application
Detergents effectively solubilize hydrophobic molecules; they are small amphipathic molecules consisting of a long alkyl chain (hydrophobic) tail attached to hydrophilic/ water solubility enhancing functional groups (a polar head). Examples include sodium dodecyl sulfate, CHAPS, and polyethylene glycol.
Applications of detergents include liposome preparation, cell lysis, analyte precipitation in solutions, solubilization of proteins and lipids, DNA & RNA extraction, as well as preventing non-specific binding in immunoassays and westerns.
The detergent type depends on the charge of the head group, whether it is ionic, non-ionic or zwitterionic.
Anionic Detergents have a negative charge and are used in DNA or RNA purification, due to their ability to disrupt cell membranes and denature proteins. However, these detergents are sensitive to ionic strength, pH and counterion nature. They may also interfere with charge-based analytical methods. Examples include:
• Sodium cholate
• Sodium deoxycholate
• Sodium glycocholate
• Sodium taurocholate
• Sodium Taurodeoxycholate
• N-lauryl sarcosine (Sarkosyl solution)
• Lithium dodecyl sulfate (LDS)
• Sodium dodecyl sulfate (SDS) (a vital component of SDS-PAGE)
Cationic Detergents have a positive charge and are therefore useful at residual anionic detergents. They can be used as surfactants in drug or vaccine delivery, while also applying to DNA extraction. Due to being characteristically germicidal, they may also be used as disinfectants. Examples include CTAB (hexadecyltrimethylammonium bromide) and TTAB (Trimethyltetradecyl ammonium bromide).
Non-ionic detergents are milder and therefore less likely to denature proteins, however shorter hydrophobic chain lengths may cause some denaturation.
• Poly (oxyethylene) ethers (& related polymers) have hydrophobic tails and a neutral, polar head group. Popular oxyethylene polymers are Tween 20 and Tween 80
• Bile Salts have a steroid core with a polar or apolar structure; they are less denaturing than similar detergents
• Glycosidic Detergents have a carbohydrate (glucose/maltose) polar head group and a nonpolar tail of between 7-14 carbons.
Zwitterionic detergents have a neutral charge and are therefore also less denaturing; critical applications are disrupting protein-protein bonds and reducing aggregation. These assets are put to good use in mass spectrometry, chromatography, electrophoresis and solubilization of cellular organelles and inclusion bodies.