Lipophilic
Encyclopedia
Lipophilicity, refers to the ability of a chemical compound
to dissolve in fat
s, oil
s, lipid
s, and non-polar solvents such as hexane
or toluene
. These non-polar solvents are themselves lipophilic — the axiom that like dissolves like generally holds true. Thus lipophilic substances tend to dissolve in other lipophilic substances, while hydrophilic (water-loving) substances tend to dissolve in water and other hydrophilic substances.
Lipophilicity, hydrophobicity, and non-polarity can describe the same tendency towards participation in the London dispersion force
as the terms are often used interchangeably. However, the terms "lipophilic" and "hydrophobic" are not synonymous, as can be seen with silicone
s and fluorocarbons, which are hydrophobic but not lipophilic.
. They have little to no capacity to form hydrogen bond
s. When a molecule of a lipophilic substance is enveloped by water, surrounding water molecules enter into an 'ice-like' structure over the greater part of its molecular surface, the thermodynamically
unfavourable event that drives oily substances out of water. Being 'driven out of water' is the quality of a substance referred to as hydrophobic (water-avoiding or water-fearing). Thus lipophilic substances tend to be water insoluble. They invariably have large o/w (oil/water) partition coefficient
s.
-based surfactants are compounds that are amphiphilic (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
) and the surfaces of the water-immiscible droplets found in o/w 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 with their head groups sticking out and their tails bunched together. Micelles 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, molecules which have a highly water interactive, ionic phosphate
head groups attached to two long alkyl tails.
By contrast, fluorosurfactant
s are not amphiphilic or detergents because fluorocarbons are not lipophilic.
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
to dissolve in fat
Fat
Fats consist of a wide group of compounds that are generally soluble in organic solvents and generally insoluble in water. Chemically, fats are triglycerides, triesters of glycerol and any of several fatty acids. Fats may be either solid or liquid at room temperature, depending on their structure...
s, oil
Oil
An oil is any substance that is liquid at ambient temperatures and does not mix with water but may mix with other oils and organic solvents. This general definition includes vegetable oils, volatile essential oils, petrochemical oils, and synthetic oils....
s, lipid
Lipid
Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...
s, and non-polar solvents such as hexane
Hexane
Hexane is a hydrocarbon with the chemical formula C6H14; that is, an alkane with six carbon atoms.The term may refer to any of four other structural isomers with that formula, or to a mixture of them. In the IUPAC nomenclature, however, hexane is the unbranched isomer ; the other four structures...
or toluene
Toluene
Toluene, formerly known as toluol, is a clear, water-insoluble liquid with the typical smell of paint thinners. It is a mono-substituted benzene derivative, i.e., one in which a single hydrogen atom from the benzene molecule has been replaced by a univalent group, in this case CH3.It is an aromatic...
. These non-polar solvents are themselves lipophilic — the axiom that like dissolves like generally holds true. Thus lipophilic substances tend to dissolve in other lipophilic substances, while hydrophilic (water-loving) substances tend to dissolve in water and other hydrophilic substances.
Lipophilicity, hydrophobicity, and non-polarity can describe the same tendency towards participation in the London dispersion force
London dispersion force
London dispersion forces is a type of force acting between atoms and molecules. They are part of the van der Waals forces...
as the terms are often used interchangeably. However, the terms "lipophilic" and "hydrophobic" are not synonymous, as can be seen with silicone
Silicone
Silicones are inert, synthetic compounds with a variety of forms and uses. Typically heat-resistant and rubber-like, they are used in sealants, adhesives, lubricants, medical applications , cookware, and insulation....
s and fluorocarbons, which are hydrophobic but not lipophilic.
Chemical bonding
Lipophilic substances interact within themselves and with other substances through the London dispersion forceLondon dispersion force
London dispersion forces is a type of force acting between atoms and molecules. They are part of the van der Waals forces...
. They have little to no capacity to form hydrogen bond
Hydrogen bond
A hydrogen bond is the attractive interaction of a hydrogen atom with an electronegative atom, such as nitrogen, oxygen or fluorine, that comes from another molecule or chemical group. The hydrogen must be covalently bonded to another electronegative atom to create the bond...
s. When a molecule of a lipophilic substance is enveloped by water, surrounding water molecules enter into an 'ice-like' structure over the greater part of its molecular surface, the thermodynamically
Thermodynamics
Thermodynamics is a physical science that studies the effects on material bodies, and on radiation in regions of space, of transfer of heat and of work done on or by the bodies or radiation...
unfavourable event that drives oily substances out of water. Being 'driven out of water' is the quality of a substance referred to as hydrophobic (water-avoiding or water-fearing). Thus lipophilic substances tend to be water insoluble. They invariably have large o/w (oil/water) partition coefficient
Partition coefficient
In chemistry and the pharmaceutical sciences, a partition- or distribution coefficient is the ratio of concentrations of a compound in the two phases of a mixture of two immiscible solvents at equilibrium. The terms "gas/liquid partition coefficient" and "air/water partition coefficient" are...
s.
Surfactants
HydrocarbonHydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....
-based surfactants are compounds that are amphiphilic (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
Surface tension is a property of the surface of a liquid that allows it to resist an external force. It is revealed, for example, in floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects to run on the water surface...
) and the surfaces of the water-immiscible droplets found in o/w 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 with their head groups sticking out and their tails bunched together. Micelles 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, molecules which have a highly water interactive, ionic phosphate
Phosphate
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...
head groups attached to two long alkyl tails.
By contrast, fluorosurfactant
Fluorosurfactant
Fluorosurfactants, or fluorinated surfactants, are synthetic organofluorine chemical compounds that have multiple fluorine atoms. They can be polyfluorinated or fluorocarbon-based . As surfactants, they are more effective at lowering the surface tension of water than comparable hydrocarbon...
s are not amphiphilic or detergents because fluorocarbons are not lipophilic.
See also
- LipophobicityLipophobicityLipophobicity, also sometimes called lipophobia, is a chemical property of chemical compounds which means "fat rejection", literally "fear of fat". Lipophobic compounds are those not soluble in lipids or other non-polar solvents...
- Lipophilic bacteriaLipophilic bacteriaLipophilic bacteria are bacteria that may proliferate in lipids.-Types:They include lipophilic corynebacteria..Propionibacterium acnes is a type of liphophilic bacteria, releasing fatty acids and worsening comedones....
- MicroemulsionMicroemulsionMicroemulsions are clear, thermodynamically stable, isotropic liquid mixtures of oil, water and surfactant, frequently in combination with a cosurfactant. The aqueous phase may contain salt and/or other ingredients, and the "oil" may actually be a complex mixture of different hydrocarbons and olefins...
- ITIESITIESITIES is an acronym used in electrochemistry for the "Interface between Two Immiscible Electrolyte Solutions". Usually, one electrolyte is an aqueous electrolyte composed of hydrophilic ions such as NaCl dissolved in water and the other electrolyte is a lipophilic salt such as tetrabutylammonium...
- Ionic partition diagramIonic partition diagramSimilar to Pourbaix's diagram for the speciation of redox species as a function of the redox potential and the pH, ionic partition diagrams indicate in which an acid or a base are predominantly present in a biphasic system as a function of the Galvani potential differencebetween the two phases and...