Summary Microsolvation- Computational Approaches to Solvation

Microsolvation- Computational
Approaches to Solvation
Imagine the environment about a solute in a water solution….
 The solute is in direct contact with a small number of water molecules,
interacting with them through hydrogen bonds, electrostatic, and van der
Waals interactions.
 This constitutes the first solvation sphere. The water molecules in the first
sphere are in direct contact with neighboring water molecules, primarily
through a hydrogen bonding network, constituting the second solvation
sphere.
 These water molecules in the second solvation sphere are weakly
interacting with the solute, but in turn are hydrogen bonded to a further
larger layer of water molecules.
 On and on this goes, creating ever larger spheres (shells) of water
molecule
 Now imagine computing the energy of this collection of solute and water
molecules
 Clearly, one must truncate the number of solvation shells to limit the
number of water molecules to some reasonable value. But just how many
water molecules are necessary to obtain bulk liquid water
 Certainly a calculation of the solute and just the first solvation shell does
not capture the effect of bulk water.
 Without the next solvation shell, the water molecules in the first shell do
not have these neighboring water molecules to interact with via hydrogen
bonding.
 The technique of including a small number of explicit solvent molecules
within the full quantum mechanical treatment can effectively treat the
most important interactions between the first solvent shell and the solute.