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Updated: Aug 11, 2026

Sedimentation Equilibrium of a Small Oligomer-forming Membrane Protein: Effect of Histidine Protonation on Pentameric Stability
Published on: April 2, 2015
Yes, pair correlations alone do determine sedimentation profiles of highly charged colloids
1Commissariat à l'Energie Atomique (CEA)/Saclay, Service de Chimie Moléculaire, Laboratoire Interdisciplinaire sur l'Organisation Nanométrique et Supramoléculaire (LIONS), 91191-Gif-sur-Yvette Cedex, France. luc@scm.saclay.cea.fr
Abstract:
Recent analyses of sedimentation profiles in charged colloidal suspensions are examined in view of general, somewhat underestimated, concepts. It is recalled that the standard equation for osmotic pressure equilibrium, which involves pair correlations between colloids only, remains valid in the presence of long-range Coulombic interactions. The entropy of the counterions and the electric field generated by the spatial inhomogeneity are implicitly taken into account in the colloid structure factor through the compressibility equation and local electroneutrality conditions. Limiting the macroscopic analysis to the pure electric-field contribution or, equivalently, to the ideal ionic pressure, corresponds to the incorrect, bare Debye-Huckel approximation for the colloid-colloid correlations. A one-component description with reasonable Derjaguin-Landau-Verwey-Overbeek-type ion-averaged effective pair potential between colloids is sufficient to derive the sedimentation profile of highly charged, weakly screened colloidal suspensions. The macroscopic electric field is directly related to the microscopic electrostatic potential around the colloids.
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