Solvation shell

A solvation shell, in physical chemistry, is a structure used to describe solvation. A solvation shell is a shell of any chemical species that acts as a solvent and surrounds a solute species. When the solvent is water it is often referred to as a hydration shell or hydration sphere.

A classic example is when water molecules form a sphere around a metal ion. The electronegative oxygen atom contained in the water molecule is attracted electrostatically to the positive charge on the metal ion. The result is a solvation shell of water molecules that surround the ion. This shell can be several molecules thick, dependent upon the charge of the ion.

Hydration shells of proteins

The hydration shell (also sometimes called hydration layer) that forms around proteins is of particular importance in biochemistry. This interaction of the protein surface with the surrounding water is often referred to as protein hydration and is fundamental to the activity of the protein. The hydration layer around a protein has been found to have dynamics distinct from the bulk water to a distance of 1 nm with effects on the surrounding water network extending beyond 2 nm. The duration of contact of a specific water molecule with the protein surface may be in the subnanosecond range while molecular dynamics simulations suggest the time water spends in the hydration shell before mixing with the outside bulk water could be in the femtosecond to picosecond range.

With other solvents and solutes, varying steric and kinetic factors can also affect the solvation shell.

Dehydrons

A dehydron is a hydrogen bond in a protein that is incompletely shielded from water attack, with a propensity to promote its own dehydration, a process both energetically and thermodynamically favored. They result from an incomplete clustering of side-chain nonpolar groups that "wrap" the polar pair within the protein structure. Dehydrons promote the removal of surrounding water through protein associations or ligand binding. Dehydrons can be identified by calculating the reversible work per unit area required to span the aqueous interface of a soluble protein, or the "epistructural tension" of the interface. Once identified, dehydrons can be used in drug discovery, both to identify new compounds and to optimize existing compounds; chemicals can be designed to "wrap" or shield dehydrons from water attack upon association with the target.

See also

• Water model
• Poisson-Boltzmann equation

References

1. ^ ^{a b} Zhang, L.; Wang, L.; Kao, Y. -T.; Qiu, W.; Yang, Y.; Okobiah, O.; Zhong, D. (2007). "Mapping hydration dynamics around a protein surface". Proceedings of the National Academy of Sciences 104 (47): 18461â€"18466. Bibcode:2007PNAS..10418461Z. doi:10.1073/pnas.0707647104. PMC 2141799. PMID 18003912. 
2. ^ Ebbinghaus, S.; Kim, S.; Heyden, M.; Yu, X.; Heugen, U.; Gruebele, M.; Leitner, D.; Havenith, M. (2007). "An extended dynamical hydration shell around proteins". Proceedings of the National Academy of Sciences of the United States of America 104 (52): 20749â€"20752. Bibcode:2007PNAS..10420749E. doi:10.1073/pnas.0709207104. PMC 2410073. PMID 18093918. 
3. ^ ^{a b c} Fernández A, Crespo A. Protein wrapping: a molecular marker for association, aggregation and drug design. Chem Soc Rev. 2008 Nov;37(11):2373-82. PMID 18949110
4. ^ Ball P. Water as an active constituent in cell biology. Chem Rev. 2008 Jan;108(1):74-108. Epub 2007 Dec 21. PMID 18095715. Page T
5. ^ Fernández A. Epistructural tension promotes protein associations. Phys Rev Lett. 2012 May 4;108(18):188102. PMID 22681121. Lay summary: Proteins hook up where water allows
6. ^ ^{a b} Ariel Fernandez. Transformative Concepts for Drug Design: Target Wrapping: Target Wrapping. Springer Science & Business Media, 2010. ISBN 978-3-642-11791-6
7. ^ Demetri GD. Structural reengineering of imatinib to decrease cardiac risk in cancer therapy. J Clin Invest. 2007 Dec;117(12):3650-3. PMID 18060025 PMC 2096446
8. ^ Sarah Crunkhorn for Nature Reviews Drug Discovery. February 2008. Research Highlight: Anticancer drugs: Redesigning kinase inhibitors.

External links

• London South Bank University pages on protein hydration
• Journal of Chemical Physics

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