Question

How does entropy drive solubility of proteins in water (or not)? Draw me a “system” of a beaker of water with and without 1) Polar solute and 2) Nonpolar solute. How does entropy change in each of the beakers before and after addition of solute?

Answer 1

This is a very simple concept actually we all know that water is a polar solvent so, when we add any non polar solvent in water it will be entropically unfavourable that is the entropy of the beakers or the system will decrease which is not favourable whereas on the other hand the polar solvents will be able to form the electrostatic bond with the water so they are favoured and an increase in entropy is seen in this case.

Now proteins are made up of amino acids now some of the amino acids they are hydrophillic like Aspartic acid, Glutamic acid, lysine etc where as others are hydrophobic like leucine, iso leucine, valine etc. Now the 3D strutcure of the proteinj determines whether it will be soluble or not mostly the globular proteins are soluble in water and the fibrous ones are not. The globular proteins are so made that there hydrophilic aa remain in the outside interacting with water but the hydrophobic aa remains in the core so entropy favours the solubility of this proteins because their polar groups interact with the water.