Gibbs-Donnan effect

Gibbs-Donnan effect

The Gibbs-Donnan effect (also known as the Donnan effect, Donnan law, Donnan equilibrium, or Gibbs-Donnan equilibrium) is a name for the behavior of charged particles near a semi-permeable membrane to sometimes fail to distribute evenly across the two sides of the membrane. [http://www.cartage.org.lb/en/themes/Reference/dictionary/Biologie/G/13.html, retrieved 28 August 2006] The usual cause is the presence of a different charged substance that is unable to pass through the membrane and thus creates an uneven electrical charge. [ [http://www.people.vcu.edu/~mikuleck/courses/gdeq/sld001.htm The Gibbs-Donnan Equilibrium...] , D.C. Mikulecky, retrieved 28 August 2006] For example, the large anionic proteins in blood plasma are not permeable to capillary walls. Because small cations are attracted-to but not bound-to the proteins, small anions will cross capillary walls more readily than small cations.

The Gibbs-Donnan effect can prevent sick cells' sodium pumps from functioning properly. [ [http://www.everything2.com/index.pl?node_id=1207400 Gibbs-Donnan effect] , Everything2.com, retrieved 28 August 2006] Some ionic species can pass through the barrier while others cannot. The solutions may be gels or colloids as well as solutions of electrolytes, and as such the phase boundary between gels, or a gel and a liquid, can also act as a selective barrier. The electric potential arising between two such solutions is called the Donnan potential.

The effect is named after the physicist Josiah Willard Gibbs and the chemist Frederick G. Donnan.

The Donnan equilibrium is prominent in the triphasic model for articular cartilage proposed by Mow and Ratcliffe, as well as in electrochemical fuel cells and dialysis.

The Donnan effect is extra osmotic pressure attributable to cations (Na+ and K+) attached to dissolved plasma proteins.

ee also

*Chemical equilibrium
*Nernst equation
*Double Layer (biospecific)
*Osmotic pressure
*Equilibrium

References

*IUPAC Compendium of Chemical Terminology 2nd Edition (1997)
*Van C. Mow and Anthony Ratcliffe "Basic Orthopedic Biomechanics", 2nd Ed. Lippincott-Raven Publishers, Philadelphia, 1997


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