File:A hydrophilic termite (Schedorhinotermes sp.) attached to the surface of a wetted citrus leaf - pone.0024368.s007.ogv

A hydrophile, from the Greek (hydros), meaning water, and φιλια (philia), meaning love, is a molecule or other molecular entity that is attracted to, and tends to be dissolved by, water. A hydrophilic molecule or portion of a molecule is one that has a tendency to interact with or be dissolved by water and other polar substances.[1][2] Hydrophilic substances can seem to attract water out of the air, the way salts (which are hydrophilic) do. Sugar, too, is hydrophilic, and like salt is sometimes used to draw water out of foods.

This is thermodynamically favorable, and makes these molecules soluble not only in water but also in other polar solvents. There are hydrophilic and hydrophobic parts of the cell membrane.

A hydrophilic molecule or portion of a molecule is one that is typically charge-polarized and capable of hydrogen bonding, enabling it to dissolve more readily in water than in oil or other hydrophobic solvents. Hydrophilic and hydrophobic molecules are also known as polar molecules and nonpolar molecules, respectively. Some hydrophilic substances do not dissolve. This type of mixture is called a colloid. Soap, which is amphipathic, has a hydrophilic head and a hydrophobic tail, allowing it to dissolve in both waters and oils.

An approximate rule of thumb for hydrophilicity of organic compounds is that solubility of a molecule in water is more than 1 mass % if there is at least one neutral hydrophile group per 5 carbons, or at least one electrically charged hydrophile group per 7 carbons.[3]

Sugar sprinkled on cut fruit will "draw out the water" through hydrophilia, making the fruit mushy and wet, as with a common strawberry compote recipe.

Hydrophilic chemicals

Liquid hydrophilic chemicals complexed with solid chemicals can be used optimize solubility of hydrophobic chemicals.

Liquid chemicals


Main article: Alcohol § Solvents

Hydroxyl groups (-OH), found in alcohols, are polar and therefore hydrophilic (water loving) but their carbon chain portion is non-polar which make them hydrophobic. The molecule increasingly becomes overall more nonpolar and therefore less soluble in the polar water as the carbon chain becomes longer.[4] Methanol has the shortest carbon chain of all alcohols (one carbon atom) followed by ethanol (two carbon atoms.)

Solid chemicals


Main article: Cyclodextrin § Uses

Cyclodextrins are used to make pharmaceutical solutions by capture hydrophobic molecules as guest host. Because inclusion compounds of cyclodextrins with hydrophobic molecules are able to penetrate body tissues, these can be used to release biologically active compounds under specific conditions.[5] For example, the Joseph Pitha study showed that when testosterone was complexed with hydroxy-propyl-beta-cyclodextrin (HPBCD), that 95% absorption of testosterone was achieved in 20 minutes via the sublingual route but HPBCD was not absorbed, whereas normally hydrophobic testosterone is absorbed less than around 40% normally via sublingual route.[6]

Hydrophilic membrane filtration

Hydrophilic membrane filtration is used in several industries to filter various liquids. These hydrophilic filters are used in the medical, industrial, and biochemical fields to filter such elements as bacteria, viruses, proteins, particulates, drugs, and other contaminates. Common hydrophilic molecules include colloids, cotton, and cellulose (which cotton consists of).

Unlike other membranes, hydrophilic membranes do not require pre-wetting. Hydrophilic membrane fabric can filter liquids in its dry state. Although most hydrophilic membranes are used in low-heat filtration processes, many new hydrophilic membrane fabrics are used to filter hot liquids and fluids.

See also