Gibbs–Donnan effect

The unequal distribution of diffusible ions across a selectively permeable membrane caused by impermeant charged particles on one side. The resulting ion balance creates a membrane potential and can alter osmotic pressure.

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Donnan equilibrium: An equilibrium in which permeant ions distribute unequally across a membrane because charged solutes cannot cross it. It expresses the ion-distribution condition underlying the effect.
Selective permeability: The property of a barrier that allows some substances to cross more readily than others. The effect requires a membrane permeable to some ions but not the charged solute.
Cell volume regulation: The processes by which cells maintain or restore their volume despite osmotic water movement. Donnan-driven osmotic pressure can make volume control necessary.
Goldman–Hodgkin–Katz equation: An equation estimating membrane voltage from ion concentrations and relative membrane permeabilities. It predicts voltage from permeability-weighted gradients rather than fixed-charge equilibrium alone.
Osmotic pressure: The pressure required to prevent net solvent flow across a semipermeable membrane. The extra particles associated with Donnan partitioning can increase osmotic pressure.
Nernst equation: An equation relating an ion’s electrochemical equilibrium potential to its concentration ratio across a membrane. It quantifies the electrical potential generated by unequal ion concentrations.
Diffusion: The net movement of particles from regions of higher concentration toward lower concentration through random motion. Diffusion redistributes permeant ions until electrical and chemical forces balance.
Plasma proteins: Proteins circulating in blood plasma, including albumin, immunoglobulins, and clotting factors. Negatively charged plasma proteins contribute to ion partitioning across capillary walls.
Active transport: The energy-dependent movement of substances across membranes against their electrochemical gradients. Donnan distributions arise passively, unlike gradients maintained by energy-consuming transport.
Donnan potential: The electrical potential difference across a membrane produced by unequal equilibrium distributions of permeant ions. It is the voltage consequence of the effect.