Surfactants (Soaps and Detergents) and Physicochemical Properties - Surface and Colloid Chemistry: Principles and Applications - page 66

length of the alkyl group of the surfactant. The magnitude of ΔG sol changes by −837
J (−200 cal)/mol, with the addition of the -CH2- group. In most cases, the addition
of electrolytes to the solution has no effect (Birdi, 1982, 1999, 2002). The kinetics of
solubilization has an effect on its applications (Birdi, 2002).
Another important aspect is that the slope in Figure 3.18 corresponds to (1/C sM ). This
allows the determination of moles SDS required to solubilize one mole of the solute.
Analyses of various solutes in SDS systems showed that
Naphthalene. 14 mol SDS/mole naphthalene
Anthracene. 780 mol SDS/mole anthracene
Phenathrene. 47 mol SDS/mole phenathrene
This kind of study allows the determination (quantitatively) of the range of solubiliza-
tion in any such application. These systems, when used to solubilize water-insoluble
organic compounds, would require such information (in such systems as pharmaceu-
tical, agriculture sprays, paints, etc.). The dosage of any substance is based on the
amount of material per volume of a solution.
Thus, this also shows that, wherever detergents are employed, the major role
(besides lower surface tension) would be the solubilization of any water-insoluble
organic compounds. This process would then assist in cleaning, or washing, or any
other effect. In some cases such as bile salts, the solubilization of lipids (especially
lecithins) gives rise to some complicated micellar structures. Due to the formation
of mixed lipid-bile salt micelles, changes are observed in CMC and aggregation
number. This has major consequences for bile salts in biology.
Dietary fat consists essentially of mixed triglycerides. These fatty lipids pass
through the stomach into the small intestine without much change in structure. In
the small intestine, triglycerides are partly hydrolyzed by an enzyme (lipase) that
leads to the formation of oil-water emulsion.
3.3.4 b I l e S a l T m I c e l l e S
Bile salts are steroids with detergent properties that are used by nature to emul-
sify lipids in foodstuff passing through the intestine to enable fat digestion and
absorption through the intestinal wall. They are secreted from the liver, stored in
the gall bladder, and passed through the bile duct into the intestine when food is
passing through. Bile salts in general form micelles with low aggregation num-
bers (ca. 10-50). However, bile micelles grow very large in size when it solubi-
lizes lipids.
Biosynthesis represents the major metabolic fate of cholesterol, accounting for
more than half of the 800 mg/day of cholesterol that the average adult uses up in met-
abolic processes. By comparison, steroid hormone biosynthesis consumes only about
50 mg of cholesterol per day. Much more that 400 mg of bile salts is required and
secreted into the intestine per day, and this is achieved by recycling them. Most of the
bile salts secreted into the upper region of the small intestine are absorbed along with
the dietary lipids that they emulsified at the lower end of the small intestine. They are