Lipophilicity (from Greek λίπος "fat" and φίλος "friendly") is 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 element ...

to dissolve in fats, oils,

lipid Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include storing ...

s, and non-polar solvents such as

hexane Hexane () or ''n''-hexane is an organic compound, a straight-chain alkane with six carbon atoms and the molecular formula C6H14. Hexane is a colorless liquid, odorless when pure, and with a boiling point of approximately . It is widely used as ...

toluene Toluene (), also known as toluol (), is a substituted aromatic hydrocarbon with the chemical formula , often abbreviated as , where Ph stands for the phenyl group. It is a colorless, water Water is an inorganic compound with the c ...

. Such compounds are called lipophilic (translated as "fat-loving" or "fat-liking"). Such non-polar solvents are themselves lipophilic, and the adage "like dissolves like" generally holds true. Thus lipophilic substances tend to dissolve in other lipophilic substances, whereas hydrophilic ("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 chemical property of a molecule (called a hydrophobe) that is seemingly repelled from a mass of water. In contrast, hydrophiles are attracted to water. Hydrophobic molecules tend to be nonpolar and, thu ...

" are not synonymous, as can be seen with

silicone In Organosilicon chemistry, organosilicon and polymer chemistry, a silicone or polysiloxane is a polymer composed of repeating units of siloxane (, where R = Organyl group, organic group). They are typically colorless oils or elastomer, rubber ...

s and fluorocarbons, which are hydrophobic but not lipophilic. __TOC__

Surfactants

Hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and Hydrophobe, hydrophobic; their odor is usually fain ...

-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 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 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 Phosphates are the naturally occurring form of the element phosphorus. In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthop ...

head groups attached to two long alkyl tails. By contrast,

fluorosurfactant Per- and polyfluoroalkyl substances (also PFAS, PFASs, and informally referred to as "forever chemicals") are a group of synthetic Organofluorine chemistry, organofluorine chemical compounds that have multiple fluorine atoms attached to an alkyl ...

s are not amphiphilic or detergents because fluorocarbons are not lipophilic. Oxybenzone, a common cosmetic ingredient often used in sunscreens, penetrates the skin particularly well 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.

References

{{Chemical solutions Chemical properties

Surfactants

See also

References