The Gibbs-Donnan equilibrium, also known as the Donnan equilibrium, is a concept in physical chemistry that describes the distribution of ions across a semi-permeable membrane. It is named after J. Willard Gibbs and Frederick G. Donnan, who independently developed the concept in the early 20th century.
At its core, the Gibbs-Donnan equilibrium describes the balance of ions on either side of a membrane that is permeable to some ions, but not to others. This can occur in a variety of situations, such as in living cells where the cell membrane acts as a semi-permeable barrier.
One important aspect of the Gibbs-Donnan equilibrium is that it takes into account the electrical charge of the ions and the concentration gradients of the ions on either side of the membrane. When an ion has a higher concentration on one side of the membrane than on the other, it will tend to move towards the side with the lower concentration in order to achieve equilibrium. However, if the ion has a net charge, it will also be influenced by the electrical potential difference across the membrane.
The Gibbs-Donnan equilibrium can be used to describe a variety of phenomena, including the movement of ions across cell membranes, the distribution of ions in soil, and the behavior of ions in colloidal systems. It is an important concept in a wide range of fields, including biochemistry, geochemistry, and materials science.
In conclusion, the Gibbs-Donnan equilibrium is a fundamental concept in physical chemistry that describes the distribution of ions across semi-permeable membranes. It takes into account both the concentration gradients and electrical potential differences of the ions, and is relevant to a wide range of fields and phenomena.
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Furthermore, if instead of being rigid the membrane is distensible, it would bulge into compartment o. Alternatively, Definition and history of the Gibbs-Donnan or just Donnan Effect One might expect it to be best defined by Frederick George Donnan himself eg. The Journal of membrane biology31. Thus, if compartment i has a greater concentration of impermeant charged species than compartment o, the three additional asymmetries that will characterize the Gibbs-Donnan equilibrium when it is reached are as follows: 1. Behold, these two compartments. Journal of Biological Chemistry265.
Last Updated on Wed, 11 May 2022 So far we have considered three of the functions that are fulfilled by the operation of Na+-K+ pumps. For them, the factor is 0. Let us now consider the characteristics of this final, time-independent, equilibrium condition, which was derived by Josiah Willard Gibbs 1839-1903 and FIGURE 23 The development of the Gibbs-Donnan equilibrium condition. This competes with the concentration gradient. The theory of the Donnan membrane equilibrium has important applications in colloid chemistry and in the technologies of leather and gelatin, but above all in the understanding of the living cell, where it can give a quantitative account of ionic equilibria both within the cell and between the cell and its environment. Das Ausmaß der Abweichung wird durch den Donnan-Koeffizient angegeben.
The increased osmotic pressure forces water to flow into the cell and tissue swelling occurs. The most thorough and definitive resource for this topic would have to be Nicholas Sperelakis' Cell Physiology Source Book, where Chapter 15 p. What is Donnan membrane effect? Now lets add some anionic protein, as before. This simplified two-compartment experiment remains an effective means of explaining the concept; to add cellular realism to this description would sacrifice clarity to accuracy. If the cells possess rigid cell walls that prevent any increase in cell volume, an osmotic pressure difference would develop across the cell walls and the cell interiors would be subjected to a pressure greater than the extracellular fluid "turgor". Now, there is an electrostatic force repelling chloride out of the intravascular compartment.
Das Donnan-Gleichgewicht beschreibt in der Donnan-Potential oder besser: Donnan-Spannung und einer Differenz des Donnan-Druck. Continue reading here: Was this article helpful? There is still unequal particle concentration on both sides of the membrane. There will be an electrical potential difference across the membrane given by the relation: If compartment i contains a preponderance of impermeant anions then Vm will be oriented such that compartment i is electrically negative with respect to compartment o; if the impermeant species are predominantly cationic, then this orientation will be reversed. In many instances, from ultrafiltration of proteins to ion exchange chromatography, the pH of the buffer adjacent to the charged groups of the membrane is different from the pH of the rest of the buffer solution. Because the membrane is permeable to Na+ and Cl", but there is no Cl" initially present in compartment i, some Cl" must diffuse from compartment o into compartment i, but this must be also accompanied by an equal amount of Na+; otherwise, electroneutrality would be violated. The same force is attracting sodium back into the intravascular compartment.
Of course, in reality this is not a true equilibrium. If one is temperamentally unsuited to piracy, one can pay for these textbooks and find these references inside them. First, they are responsible for the high K+ and low Na+ concentrations characteristic of the intracellular fluid of higher animals. The attractive force of anionic protein for sodium competes with the concentration gradient sucking it back into the interstitial compartment. The opposing Donnan effects cause chloride ions to migrate inside the cell, increasing the intracellular chloride concentration. As a result, a second Donnan effect this time with the non-diffusible ions being extracellular sodium is established across the membrane, which maintains an osmotic counter-gradient for water movement. The Donnan effect which is named after the British chemist Frederick George Donnan Donnan 1911, 1995 is related to the presence of impermeant ions i.
Gibbsdonnan Equilibrium Ion Pumps And Maintenance Of Cell Volume
In short, wherever a membrane separates compartments and isolates a non-diffusible substance within one of them, we can find some application of the Gibbs-Donnan effect. Finally, if we consider the initial and final conditions together with Eq. These pumps serve to lower the intracellular concentration of permeant solutes and thereby balance and offset the osmotic effects of impermeant intracellular macromolecules. The membrane voltage will become zero, but the chemical gradient will still exist. Recall that inhibition of the pump would not only lead to the dissipation of the asymmetric distributions of Na+ and K+, but also the Vm cell interior negative arising from these asymmetries.
For exam purposes, the CICM trainee would be advised to avoid terms like "osmoexplosion"; the formal statement would be that "ATP-powered sodium pumps decrease intracellular osmolality by actively transporting sodium out of the intracellular fluid, thereby maintaining cell volume homeostasis via a second Donnan effect". Because the intracellular concentration of charged, largely anionic, impermeant macromolecules is much greater than that in the extracellular fluid, cells lacking ion pumps would resemble the passive system illustrated in Fig. Assumptions of Donnan Membrane Equilibrium: i The charge distribution is uniform throughout the colloidal system. In equilibrium dialysis, with a nondiffusible, charged protein on one side of the membrane, Donnan equilibrium leads to a pH difference across the membrane. In higher animals, the osmolarity of the extracellular fluid is carefully regulated by the kidneys in response to neurohormonal stimuli so that it normally remains within very narrow limits. What are the assumptions of Donnan membrane equilibrium? If one were that way inclined, one might be able to represent this equilibrium as an equation, where "int" means intracellular and "ext" means extracellular. A number of enzymes involved in intermediary metabolism and protein synthesis appear to require relatively high concentrations of K+ for optimal activity and are inhibited by high concentra tions of Na+; the activities of these enzymes would be markedly impaired if the intracellular Na+ and K+ concentrations were the same as those in the extracellular fluid.
The value of this factor for monovalent cations is 0. Now, intracellular and extracellular concentrations of potassium remain the same and so the potassium is not inclined to diffuse anywhere , but now there is a concentration gradient for the chloride ions. If the membrane is rigid then an osmotic pressure would balance that driving force; if the membrane is distensible, then it would bulge into compartment o. A contribution to physical-chemical physiology , Zeitschrift für Elektrochemie und angewandte physikalische Chemie, 17 10 : 572-581. The relationship between the Donnan effect and the published works by Gibbs was unearthed "a man of genius, combining profound insight with the highest powers of logical reasoning" "not an advertiser for personal renown". Water is osmotically attracted into the vascular compartment. This W3C-unspecified Licensing Public domain Public domain false false I, the copyright holder of this work, release this work into the In some countries this may not be legally possible; if so: I grant anyone the right to use this work for any purpose, without any conditions, unless such conditions are required by law.
Thus, there will be an osmotic driving force for the movement of water into compartment i. Furthermore, it follows from Eq. Journal of Membrane Science100. What is the relationship of Donnan membrane equilibrium with pH? The system is then left undisturbed for a sufficiently long time until equilibrium is achieved. So there is no stable steady state. This chapter is vaguely relevant to Section E i of the "explain mechanisms of transport of substances across cell membranes, including an understanding of the Gibbs-Donnan effect". Consequently, more chloride collects in the interstitial fluid.
But it is hard to argue against knowing a little bit about this protein, as it certainly seems rather central to all cellular life. As a result, a second Donnan effect this time with the non-diffusible ions being extracellular sodium is established across the membrane, which maintains an osmotic counter-gradient for water movement. Donnan effect DE Diffusible anions are expelled. Donnan never called his effect "the Donnan effect", but from 1911 onward it became known as such, and at this stage there was zero Gibbs in the public mentions of this concept. The presence of impermeant ions on one side of the membrane creates an osmotic diffusion gradident attracting water into that compartment. The distribution of ions in the interstitial and intravascular compartments can be expressed in terms of a coefficient factor which describes the distribution of the ion in the interstitial fluid as a proportion of its concentration in the plasma.
