Solvation shell

The first solvation shell of a sodium ion dissolved in water

A Solvation shell is a shell of any chemical species acting as a solvent, surrounding a solute species. When the solvent is water it is often referred to as a hydration shell or hydration sphere.

A classic example is water molecules solvating a metal ion. The electronegative oxygen atom contained in the water molecule attracts electrostatically to the positive charge on the metal ion. The result is a 'solvation shell' of water molecules surrounding the ion. This shell can be several molecules thick, dependent on 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.

See also

• Water model
• Poisson-Boltzmann equation

External links

• London South Bank University pages on protein hydration