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( Lipophilicity)
Lipophilicity, fat-liking, refers to the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene.[1] 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 (the latter as used to describe intermolecular interactions and not the separation of charge in dipoles) all essentially describe the same molecular attribute; the terms are often used interchangeably.[citation needed] However, the terms "lipophilic" and "hydrophobic" are not synonymous, as can be seen with silicones, which are hydrophobic but not lipophilic. Lipophilic substances interact within themselves and with other substances through van der Waals forces. They have little to no capacity to form hydrogen bonds. 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 coefficients. 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.
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