Question

what are the physical and chemical properties of detergents? please send urgently

Answer 1

concentration at which micelles begin to form is the critical micelle concentration (CMC). The CMC is the maximum monomer concentration and constitutes a measure of the free energy of micelle formation. The lower the CMC, the more stable the micelle and the more slowly molecules are incorporated into or removed from the micelle. The structure of the hydrophobic region of the detergent can affect the micelle structure. An increase in the length of the hydrophobic hydrocarbon chain of ionic detergents results in an increased micelle size and a lower CMC, as fewer molecules are needed to construct a micelle.

The average number of monomers in a micelle is the aggregation number. The CMC and aggregation number values are highly dependent on factors such as temperature, pH, ionic strength, and detergent homogeneity and purity. Slight discrepancies in reported values for CMC and aggregation number may be the result of variations in the analytical methods used to determine the values. Aggregation number values are also shifted by concentration, since the number of detergent molecules per micelle may increase if the concentration is above the CMC.

Ease of removal or exchange is an important factor in the selection of a detergent. Some of the more common detergent removal methods include:

DialysisGel filtration chromatographyHydrophobic adsorption chromatographyProtein precipitation

 

The CMC value associated with the detergent is a useful guide to hydrophobic binding strength. Detergents with higher CMC values have weaker binding and are subsequently easier to remove by dialysis or displacement methods. Detergents with low CMC values require less detergent in order to form micelles and solubilize proteins or lipids.

Another useful parameter when evaluating detergents for downstream removal is the micelle molecular weight, which indicates relative micelle size. Smaller micelles are more easily removed and are usually desirable when protein-detergent complexes are to be separated based on the molecular size of the protein. The micelle molecular weight may be calculated by multiplying the aggregation number by the monomer molecular weight.

The cloud point is the temperature at which the detergent solution near or above its CMC separates into two phases. The micelles aggregate, typically forming a cloudy phase with high detergent concentration, while the balance of the solution becomes detergent-depleted. The resulting two-phase solution can be separated, with the extracted protein being located in the detergent-rich phase. Detergents with low cloud point temperatures, such as TRITON® X-114 (cloud point ~23 °C) are recommended for use with proteins since high cloud point temperatures may denature solubilized proteins. The cloud point can be affected by changes in detergent concentration, temperature, and the addition of salt or polymers such as dextran and polyethylene glycol. Note that the detergent-rich phase is also contingent on the specific detergent(s) and salt concentration; under some conditions the phase may be clear rather than cloudy and be located as either the upper or lower phase of the solution. In non-ionic detergents, this behavior has been applied in the phase separation and purification of membrane proteins.2