The addition of a small amount of a salt, such as (NH4)2SO4, to a solution containing a charged protein increases the solubility of the protein in water. This observation is called the salting-in effect. However, the addition of large amounts of salt can decrease the solubility of the protein to such an extent that the protein precipitates from solution. This observation is called the salting-out effect and is used widely by biochemists to isolate and purify proteins. Consider the equilibrium PXν(s) ⇋ Pν+(aq) + ν X−(aq), where Pν+ is a polycationic protein of charge ν+ and X− is its counterion. Use Le Chatelier’s principle and the physical principles behind the Debye–Hückel theory to provide a molecular interpretation for the salting-in and salting-out effects.

The addition of a small amount of a salt, such as (NH4)2SO4, to a solution containing a charged protein increases the solubility of the protein in water. This observation is called the salting-in effect. However, the addition of large amounts of salt can decrease the solubility of the protein to such an extent that the protein precipitates from solution. This observation is called the salting-out effect and is used widely by biochemists to isolate and purify proteins. Consider the equilibrium PXν(s) ⇋ Pν+(aq) + ν X−(aq), where Pν+ is a polycationic protein of charge ν+ and X− is its counterion. Use Le Chatelier’s principle and the physical principles behind the Debye–Hückel theory to provide a molecular interpretation for the salting-in and salting-out effects.

Chemistry: The Molecular Science

5th Edition

ISBN:9781285199047

Author:John W. Moore, Conrad L. Stanitski

Publisher:John W. Moore, Conrad L. Stanitski

Chapter11: Chemical Kinetics: Rates Of Reactions

Section: Chapter Questions

Problem 83QRT

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