Lipophilicity (from
Greek λίπος "fat" and
φίλος "friendly"), refers to the ability of a
chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one elemen ...
to dissolve in
fat
In nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such compounds, most commonly those that occur in living beings or in food.
The term often refers specifically to triglycerides (triple est ...
s,
oil
An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...
s,
lipids, and
non-polar solvents such as
hexane
Hexane () is an organic compound, a straight-chain alkane with six carbon atoms and has the molecular formula C6H14.
It is a colorless liquid, odorless when pure, and with boiling points approximately . It is widely used as a cheap, relatively ...
or
toluene. Such non-polar solvents are themselves lipophilic (translated as "fat-loving" or "fat-liking"
), and the axiom that "like dissolves like" generally holds true. Thus lipophilic substances tend to dissolve in other lipophilic substances, but
hydrophilic
A hydrophile is a molecule or other molecular entity that is attracted to water molecules and tends to be dissolved by water.Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon'' Oxford: Clarendon Press.
In contrast, hydrophobes are no ...
("water-loving") substances tend to dissolve in water and other hydrophilic substances.
Lipophilicity, hydrophobicity, and non-polarity may describe the same tendency towards participation in the
London dispersion force, as the terms are often used interchangeably. However, the terms "lipophilic" and "
hydrophobic
In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water.
Hydrophobic molecules tend to be nonpolar and, t ...
" are not synonymous, as can be seen with
silicones and
fluorocarbons, which are hydrophobic but not lipophilic.
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Surfactants
Hydrocarbon-based
surfactants are compounds that are
amphiphilic
An amphiphile (from the Greek αμφις amphis, both, and φιλíα philia, love, friendship), or amphipath, is a chemical compound possessing both hydrophilic (''water-loving'', polar) and lipophilic (''fat-loving'') properties. Such a compoun ...
(or amphipathic), having a hydrophilic, water interactive "end", referred to as their "head group", and a lipophilic "end", usually a long chain hydrocarbon fragment, referred to as their "tail". They congregate at low energy surfaces, including the air-water interface (lowering
surface tension
Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension is what allows objects with a higher density than water such as razor blades and insects (e.g. water striders) to ...
) and the surfaces of the water-immiscible droplets found in oil/water
emulsions (lowering interfacial tension). At these surfaces they naturally orient themselves with their head groups in water and their tails either sticking up and largely out of water (as at the air-water interface) or dissolved in the water-immiscible phase that the water is in contact with (e.g. as the emulsified oil droplet). In both these configurations the head groups strongly interact with water while the tails avoid all contact with water. Surfactant molecules also aggregate in water as
micelles
A micelle () or micella () (plural micelles or micellae, respectively) is an aggregate (or supramolecular assembly) of surfactant amphipathic lipid molecules dispersed in a liquid, forming a colloidal suspension (also known as associated coll ...
with their head groups sticking out and their tails bunched together.
Micelles
A micelle () or micella () (plural micelles or micellae, respectively) is an aggregate (or supramolecular assembly) of surfactant amphipathic lipid molecules dispersed in a liquid, forming a colloidal suspension (also known as associated coll ...
draw oily substances into their hydrophobic cores, explaining the basic action of soaps and detergents used for personal cleanliness and for laundering clothes. Micelles are also biologically important for the transport of fatty substances in the small intestine surface in the first step that leads to the absorption of the components of fats (largely fatty acids and 2-monoglycerides).
Cell membranes are bilayer structures principally formed from
phospholipids
Phospholipids, are a class of lipids whose molecule has a hydrophilic "head" containing a phosphate group and two hydrophobic "tails" derived from fatty acids, joined by an alcohol residue (usually a glycerol molecule). Marine phospholipids ...
, molecules which have a highly water interactive, ionic
phosphate head groups attached to two long alkyl tails.
By contrast,
fluorosurfactant
Per- and polyfluoroalkyl substances (PFASs) are synthetic organofluorine chemical compounds that have multiple fluorine atoms attached to an alkyl chain. An early definition, from 2011, required that they contain at least one perfluoroalkyl ...
s are not amphiphilic or
detergents because fluorocarbons are not lipophilic.
Oxybenzone, a common cosmetic ingredient often used in sunscreens, is particularly penetrative because it is not very lipophilic. Anywhere from 0.4% to 8.7% of oxybenzone can be absorbed after one topical sunscreen application, as measured in urine excretions.
[H. Gonzalez, H., Farbrot, A., Larko. O., and Wennberg, A. M. (2006), Percutaneous absorption of the sunscreen benzophenone-3 after repeated whole-body applications, with and without ultraviolet irradiation. British Journal of Dermatology, 154:337-340.]
See also
*
Lipophobicity Lipophobicity, also sometimes called lipophobia (from the Greek λιποφοβία from λίπος ''lipos'' "fat" and φόβος ''phobos'' "fear"), is a chemical property of chemical compounds which means " fat rejection", literally "fear of fat". ...
*
Lipophilic bacteria Lipophilic bacteria (''fat-loving bacteria'') are bacteria that may proliferate in lipids.
Types
They include lipophilic corynebacteria.
''Cutibacterium acnes'' is a type of lipophilic bacteria, releasing fatty acids and worsening comedones in a ...
*
Microemulsion Microemulsions are clear, thermodynamically stable isotropic liquid mixtures of oil, water and surfactant, frequently in combination with a cosurfactant. The aqueous phase may contain salt(s) and/or other ingredients, and the "oil" may actually be ...
*
ITIES
In electrochemistry, ITIES (interface between two immiscible electrolyte solutions) is an electrochemical interface that is either polarisable or polarised. An ITIES is polarisable if one can change the Galvani potential difference, or in other wo ...
*
Ionic partition diagram
References
{{Chemical solutions
Chemical properties