Kosmotropic

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Solutes are defined as kosmotropic if they contribute to the stability and structure of water-water interactions. Kosmotropes cause water molecules to favorably interact, which also stabilizes intermolecular interactions in macromolecules such as proteins.

[edit] Ionic Kosmotropes

Ionic kosmotropes tend to be small or have high charge density. Some ionic kosmotropes are sulfate, phosphate, magnesium(2+) and lithium(1+). Large ions or ions with low charge density (such as bromide, iodide, potassium(1+), caesium(1+)) instead act as chaotropes.

A scale can be established if one refers to the Hofmeister series or looks up the free energy of hydration ( $Δ G hydr$ ) of the salts. The more negative $Δ G hydr$ , the more kosmotropic the salt.

[edit] Nonionic Kosmotropes

See also: chaotropic

Nonionic kosmotropes have no net charge but are very soluble and become very hydrated. Carbohydrates such as trehalose and glucose as well as proline and tert-butanol are kosmotropes.