Lipophilicity

Lipophilicity (from Greek λίπος "fat" and φίλος "friendly"), refers to the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene. Such non-polar solvents are themselves lipophilic (translated as "fat-loving" or "fat-liking"[1][2]), and the axiom that "like dissolves like" generally holds true. Thus lipophilic substances tend to dissolve in other lipophilic substances, but 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" are not synonymous, as can be seen with silicones and fluorocarbons, which are hydrophobic but not lipophilic.

Surfactants

Hydrocarbon-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 head groups attached to two long alkyl tails.

By contrast, fluorosurfactants 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.[3] Anywhere from 0.4% to 8.7% of oxybenzone can be absorbed after one topical sunscreen application, as measured in urine excretions.[4]

gollark: The current structure is at least kind of good because most devices don't need a very big routing table and most devices can pay a flat rate for connectivity.
gollark: If you had a map of the entire network it would just be Dijkstra or something, but that would be bad.
gollark: The jamming issue there might be disincentivizable with some sort of automatic price adjustment mechanism, but aaaaaaaaaaaa.
gollark: I think stuff kind of works if you just let nodes set their own prices (except you are still incentivized to jam people randomly, for arbitrage or otherwise), but that's just the regular internet.
gollark: (with you as C, and with B unable to reach A directly now)

See also

References
  1. Compendium of Chemical Terminology, lipophilic, accessed 15 Jan 2007.
  2. Alyn William Johnson (1999). Invitation to Organic Chemistry. Jones & Bartlett Learning. p. 283. ISBN 978-0-7637-0432-2.
  3. Hanson KM, Gratton E, Bardeen CJ. 2006. Sunscreen enhancement of UV-induced reactive oxygen species in the skin. Free Radical Biology & Medicine 41(8): 1205-1212
  4. 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.
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