Amphiphile is a term describing a chemical compound possessing both
hydrophilic and lipophilic properties. Such a compound is called amphiphilic or
amphipathic. This forms the basis for a number of areas of research in chemistry
and biochemistry, notably that of lipid polymorphism. Organic compounds
containing hydrophilic groups at both ends of a prolate molecule are called
bolaamphiphilic. Common amphiphilic substances are soaps, detergents and
lipoproteins. Structure and properties
The lipophilic group is typically a large hydrocarbon moiety, such as a long
chain of the form CH3(CH2)n, with n > 4. The hydrophilic group falls into one of
the following categories: Charged groups
Anionic. Examples, with the lipophilic part of the molecule represented by an
R, are: carboxylates: RCO2−;
sulfates: RSO4−; sulfonates: RSO3−.
phosphates: The charged functionality in phospholipids.
Cationic. Examples: ammoniums: RNH3+.
Polar, uncharged groups. Examples are alcohols with large R groups, such as
diacyl glycerol, and oligoethyleneglycols with long alkyl
chains. Often, amphiphilic species have several
lipophilic parts, several hydrophilic parts, or several of both. Proteins and
some block copolymers are such examples. Amphiphilic compounds have lipophilic
structures and hydrophilic polar functional groups.
As a result of having both lipophilic and hydrophilic portions, some
amphiphilic compounds may dissolve in water and to some extent in non-polar
organic solvents. When placed in an immiscible biphasic
system consisting of aqueous and organic solvents, the amphiphilic compound will
partition the two phases. The extent of the hydrophobic and hydrophilic portions
determines the extent of partitioning. Biological role
Phospholipids, a class of amphiphilic molecules, are the main components of
biological membranes. The amphiphilic nature of these molecules defines the
way in which they form membranes. They arrange themselves into bilayers, by
positioning their polar groups towards the surrounding aqueous medium, and
their lipophilic chains towards the inside of the bilayer, defining a
non-polar region between two polar ones.Biology Online
Although phospholipids are principal constituents of biological membranes,
there are other constituents, such as cholesterol and glycolipids, which are
also included in these structures and give them different physical and
biological properties. Many other amphiphilic compounds, such
as pepducins, strongly interact with biological membranes by insertion of the
hydrophobic part into the lipid membrane, while exposing the hydrophilic
part to the aqueous medium, altering their physical behavior and sometimes
disrupting them. Examples of amphiphiles
There are several examples of molecules that present amphiphilic properties:
Hydrocarbon based surfactants are an example group of amphiphilic compounds.
Their polar region can be either ionic, or non-ionic. Some typical members of
this group are: sodium dodecyl sulfate, Benzalkonium chloride, Cocamidopropyl
betaine and 1-octanol. Many biological compounds are
amphiphilic: phospholipids, cholesterol, glycolipids, fatty acids, bile acids,
saponins, local anaesthetics etc. References
External links Estimating intestinal permeability by
surface activity profiling See also
Hydrophile, hydrophilic Wetting
Free surface energy Sodium dodecyl sulfate
Surfactant Amphipathic lipids
Polymorphism Bubbles in Abiogenesis