Amphiphile
An amphiphile (from the Greek αμφις amphis, both, and φιλíα
Amphiphiles are 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 the molecule are called
Structure
The
The
- charged groups
- anionic. Examples, with the lipophilic part of the molecule represented by R, are:
- carboxylates: RCO2−
- sulfates: RSO4−
- sulfonates: RSO3−
- phosphates (the charged functional group in phospholipids)
- cationic. Examples:
- ammoniums: RNH3+
- polar, uncharged groups. Examples are alcohols with large R groups, such as diacyl glycerol (DAG), and oligo ethylene glycol 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.[citation needed]
Amphiphilic compounds have lipophilic (typically hydrocarbon) structures and hydrophilic polar functional groups (either ionic or uncharged).[citation needed]
As a result of having both lipophilic and hydrophilic portions, some amphiphilic compounds may dissolve in water and to some extent in
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.[citation needed]
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 lipid bilayers, by forming a sheet composed of two layers of lipids. Each layer forms by positioning their lypophilic chains to the same side of the layer. The two layers then stack such that their lyphphilic chains touch on the inside and their polar groups are outside facing the surrounding aqueous media. Thus the inside of the bilayer sheet is a non-polar region sandwiched between the two polar sheets.[2]
Although phospholipids are the principal constituents of biological membranes,[3] there are other constituents, such as cholesterol and glycolipids, which are also included in these structures and give them different physical and biological properties.[citation needed]
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.[citation needed]
Aβ proteins form antiparallel β sheets which are strongly amphiphilic,[4] and which aggregate to form toxic oxidative Aβ fibrils. Aβ fibrils themselves are composed of amphiphilic 13-mer modular β sandwiches separated by reverse turns. Hydropathic waves optimize the description of the small (40,42 aa) plaque-forming (aggregative) Aβ fragments.[5]
Examples
There are several examples of molecules that present amphiphilic properties:
Many biological compounds are amphiphilic: phospholipids, cholesterol, glycolipids, fatty acids, bile acids, saponins, local anaesthetics, etc.[citation needed]
Soap is a common household amphiphilic surfactant compound. Soap mixed with water (polar, hydrophilic) is useful for cleaning oils and fats (non-polar, lipiphillic) from kitchenware, dishes, skin, clothing, etc.
See also
- Amphoterism
- Bubbles in abiogenesis
- Emulsion
- Free surface energy
- Surfactant
- Lipid polymorphism
- Sodium dodecyl sulfate
- Wetting
- Viral envelope
References
- ISBN 978-1-947172-04-3. Retrieved 14 May 2023.
- ^ "Amphipathic". Biology-Online Dictionary. Retrieved 2016-11-17.
- ^ "Structure of a Membrane". The Lipid Chronicles. 5 November 2011. Retrieved 2020-06-02.
- PMID 7892213.
- PMID 25702750.
- PMID 29165350.