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Amphiphile (from the Greek αμφις, amphis: both and φιλíα, philia: love, friendship) is a term describing a chemical compound possessing both hydrophilic and hydrophobic nature. A compound with such properties is called amphiphilic. Term amphipathic is synonymous to amphiphilic.
How is it possible?
Molecules of amphiphilic compounds have hydrophobic (usually of hydrocarbon nature) and hydrophilic (represented by either ionic or uncharged polar functional groups) structural regions.
As a result of having both hydrophobic and hydrophilic structural regions, 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 hydrophobic solvent the amphiphilic compound will partition between the two phases. The balance between hydrophobic and hydrophilic natures defines the extent of partitioning.
Biological role
Phospholipids, a class of amphiphilic molecules, are the main components of biological membranes. The amphiphilic nature of this 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 hydrophobic chains towards the inside of the bilayer, defining a non-polar region between two polar ones.
Although phospholipids are principal constituents of biological membranes, there are other amphiphilic molecules, such as cholesterol and glycolipids, which are also included in these structures and give them different physical and biological properties.
Many other amphiphilic compounds strongly interact with biological membranes by insertion of hydrophobic part into the lipid membrane, while exposing the hydrophilic part to the aqueous medium, altering their physical behaviour and sometimes disrupting them.
Examples of Amphiphiles
There are several examples of molecules that present amphiphilic properties:
Surfactants are an example group of amphiphilic compounds. Their polar region can be either ionic, or non-ionic. Some typical members of this goup are: sodium dodecyl sulphate (anionic), Benzalkonium chloride (cationic), Cocamidopropyl betaine (zwitterionic) and octanol (long chain alcohol, non-ionic).
Many biological compounds are amphiphilic by nature: phospholipids, cholesterol, glycolipids, fatty acids, bile acids, saponins, etc.
See also
"Amphiphiles"