Kosmotropic
Co-solvents (in water
Ionic kosmotropes
Ionic kosmotropes tend to be small or have high charge density. Some ionic kosmotropes are CO2−
3, SO2−
4, HPO2−
4, Mg2+
, Li+
, Zn2+
and Al3+
. Large ions or ions with low charge density (such as Br−
, I−
, K+
, Cs+
) instead act as chaotropes.[2] Kosmotropic anions are more polarizable and hydrate more strongly than kosmotropic cations of the same charge density.[3]
A scale can be established if one refers to the Hofmeister series or looks up the free energy of hydrogen bonding () of the salts, which quantifies the extent of hydrogen bonding of an ion in water.[4] For example, the kosmotropes CO2−
3 and OH−
have between 0.1 and 0.4 J/mol, whereas the chaotrope SCN−
has a between −1.1 and −0.9.[4]
Recent simulation studies have shown that the variation in solvation energy between the ions and the surrounding water molecules underlies the mechanism of the Hofmeister series.[5][6] 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.[6]
Applications
Ammonium sulfate 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.[7][citation needed]
Nonionic kosmotropes
Nonionic kosmotropes have no net charge but are very soluble and become very hydrated. Carbohydrates such as
See also
- Chaotropic agent and guanidinium chloride
- Protein precipitation, on ammonium sulfate "salting out"
References
- ^ PMID 15501575.
- ^ Chaplin, Martin (May 17, 2014). "Kosmotropes and Chaotropes". Water Structure and Science. London South Bank University. Archived from the original on 2014-09-05. Retrieved 2014-09-05.
- PMID 19409939.
- ^ PMID 19236019.
- PMID 28816050.
- ^ PMID 29611710.
- PMC 7326125.
External links
- Polson, C; Sarkar, P; Incledon, B; Raguvaran, V; Grant, R (2003). "Optimization of protein precipitation based upon effectiveness of protein removal and ionization effect in liquid chromatography-tandem mass spectrometry". Journal of Chromatography B. 785 (2): 263–275. PMID 12554139.