kosmotropic
{{Short description|Agents which contribute to stability of water-water interactions}}
Co-solvents (in water solvent) are defined as kosmotropic (order-making) if they contribute to the stability and structure of water-water interactions. In contrast, chaotropic (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 such as proteins.{{cite journal |vauthors=Moelbert S, Normand B, De Los Rios P | title=Kosmotropes and chaotropes: modelling preferential exclusion, binding and aggregate stability | journal= Biophysical Chemistry | volume=112 | issue=1 | year=2004 | pages=45–57 | pmid=15501575 | doi=10.1016/j.bpc.2004.06.012| arxiv=cond-mat/0305204 }}
Ionic kosmotropes
Ionic kosmotropes tend to be small or have high charge density. Some ionic kosmotropes are carbonate, sulfate, phosphate, magnesium, lithium, zinc and aluminium. Large ions or ions with low charge density (such as bromide, iodide, potassium, caesium) instead act as chaotropes.{{cite web |last = Chaplin |first = Martin |title = Kosmotropes and Chaotropes |work = Water Structure and Science |publisher = London South Bank University |date = May 17, 2014 |url = http://www1.lsbu.ac.uk/water/kosmos.html |access-date = 2014-09-05 |archive-date = 2014-09-05 |archive-url = https://web.archive.org/web/20140905191542/http://www1.lsbu.ac.uk/water/kosmos.html |url-status = dead }} Kosmotropic anions are more polarizable and hydrate more strongly than kosmotropic cations of the same charge density.{{cite journal |author=Yang Z |title=Hofmeister effects: an explanation for the impact of ionic liquids on biocatalysis |journal= Journal of Biotechnology |volume=144 |issue=1 |year=2009 |pages=12–22 |doi=10.1016/j.jbiotec.2009.04.011 |pmid=19409939}}
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.{{cite journal |author=Marcus Y |title=Effect of ions on the structure of water: structure making and breaking | journal= Chemical Reviews |volume=109 |issue=3 |year=2009 |pages=1346–1370 |doi=10.1021/cr8003828 |pmid=19236019}} For example, the kosmotropes carbonate and hydroxide have between 0.1 and 0.4 J/mol, whereas the chaotrope Thiocyanate has a 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 Hofmeister series.{{cite journal |author=M. Adreev |author2=A. Chremos |author3=J. de Pablo |author4=J. F. Douglas |title=Coarse-Grained Model of the Dynamics of Electrolyte Solutions |journal=J. Phys. Chem. B |volume=121 |issue=34 |pages=8195–8202 |year=2017 |doi=10.1021/acs.jpcb.7b04297 |pmid=28816050}}{{cite journal |author=M. Adreev|author2=J. de Pablo |author3=A. Chremos |author4=J. F. Douglas |title=Influence of Ion Solvation on the Properties of Electrolyte Solutions |journal=J. Phys. Chem. B |volume=122 |issue=14 |pages=4029–4034 |year=2018 |doi=10.1021/acs.jpcb.8b00518 |pmid=29611710}} 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 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.{{cite journal |last1=Hillebrandt |first1=Nils |last2=Vormittag |first2=Philipp |last3=Bluthardt |first3=Nicolai |last4=Dietrich |first4=Annabelle |last5=Hubbuch |first5=Jürgen |title=Integrated Process for Capture and Purification of Virus-Like Particles: Enhancing Process Performance by Cross-Flow Filtration |journal=Frontiers in Bioengineering and Biotechnology |date=25 May 2020 |volume=8 |pages=489 |doi=10.3389/fbioe.2020.00489|pmc=7326125 |doi-access=free }}{{Citation needed|date=September 2014}}
Nonionic kosmotropes
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.
See also
- Chaotropic agent and guanidinium chloride
- Protein precipitation, on ammonium sulfate "salting out"
References
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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}}