Co-solvents (in water

solvent A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...

) are defined as kosmotropic (order-making) if they contribute to the stability and structure of water-water interactions. In contrast,

chaotropic Chaotropicity describes the entropic disordering of lipid bilayers and other biomacromolecules which is caused by substances dissolved in water. According to the original usage and work carried out on cellular stress mechanisms and responses, ch ...

(disorder-making) agents have the opposite effect, disrupting water structure, increasing the solubility of nonpolar solvent particles, and destabilizing solute aggregates. Kosmotropes cause water molecules to favorably interact, which in effect stabilizes intramolecular interactions in

macromolecules A macromolecule is a "molecule of high relative molecular mass, the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of low relative molecular mass." Polymers are physi ...

such as

proteins Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, re ...

Ionic kosmotropes

Ionic kosmotropes tend to be small or have high charge density. Some ionic kosmotropes are , , , , , and . Large ions or ions with low charge density (such as , , , ) instead act as chaotropes. Kosmotropic

anions An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

are more polarizable and hydrate more strongly than kosmotropic

cations An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

of the same charge density. A scale can be established if one refers to the

Hofmeister series The Hofmeister series or lyotropic series is a classification of ions in order of their lyotrophic properties, which is the ability to salt out or salt in proteins. The effects of these changes were first worked out by Franz Hofmeister, who s ...

or looks up the free energy of

hydrogen bond In chemistry, a hydrogen bond (H-bond) is a specific type of molecular interaction that exhibits partial covalent character and cannot be described as a purely electrostatic force. It occurs when a hydrogen (H) atom, Covalent bond, covalently b ...

ing (

\Delta G_

) of the salts, which quantifies the extent of hydrogen bonding of an ion in water. For example, the kosmotropes and have

\Delta G_

between 0.1 and 0.4 J/mol, whereas the chaotrope has a

\Delta G_

between −1.1 and −0.9. Recent simulation studies have shown that the variation in solvation energy between the ions and the surrounding water molecules underlies the mechanism of the

. Thus, ionic kosmotropes are characterized by strong solvation energy leading to an increase of the overall cohesiveness of the solution, which is also reflected by the increase of the viscosity and density of the solution.

Applications

Ammonium sulfate Ammonium sulfate (American English and international scientific usage; ammonium sulphate in British English); (NH4)2SO4, is an inorganic salt with a number of commercial uses. The most common use is as a soil fertilizer. It contains 21% nitrogen a ...

is the traditional kosmotropic salt for the salting out of protein from an aqueous solution. Kosmotropes are used to induce protein aggregation in pharmaceutical preparation and at various stages of protein extraction and purification.

Nonionic kosmotropes

Nonionic kosmotropes have no net charge but are very soluble and become very hydrated. Carbohydrates such as

trehalose Trehalose (from Turkish '' tıgala'' – a sugar derived from insect cocoons + -ose) is a sugar consisting of two molecules of glucose. It is also known as mycose or tremalose. Some bacteria, fungi, plants and invertebrate animals synthesize it ...

and

glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecular formula , which is often abbreviated as Glc. It is overall the most abundant monosaccharide, a subcategory of carbohydrates. It is mainly made by plants and most algae d ...

, as well as

proline Proline (symbol Pro or P) is an organic acid classed as a proteinogenic amino acid (used in the biosynthesis of proteins), although it does not contain the amino group but is rather a secondary amine. The secondary amine nitrogen is in the p ...

and ''tert''-butanol, are kosmotropes.

References

External links

* {{cite journal, pmid=12554139, year=2003, last1=Polson, first1=C, last2=Sarkar, first2=P, last3=Incledon, first3=B, last4=Raguvaran, first4=V, last5=Grant, first5=R, title=Optimization of protein precipitation based upon effectiveness of protein removal and ionization effect in liquid chromatography-tandem mass spectrometry, volume=785, issue=2, pages=263–275, journal=Journal of Chromatography B , doi=10.1016/S1570-0232(02)00914-5 Chemical properties

Ionic kosmotropes

Applications

Nonionic kosmotropes

See also

References

External links