Analysis of steric partition behavior of molecules in membranes using statistical physics. Application to gel chromatography and electrophoresis

Abstract

The principles of statistical physics are used to formulate general expressions for the steric partition behavior of molecules in both random and ordered membrane structures that may be applied to any shape of the solute and/or the volume-excluding element of the membrane. These expressions fully define partitioning in terms of the volume excluded to point molecules and to finite-sized molecules. The mean effective exclusion volume for a molecule is calculated as a function of a global interaction energy, which varies with position, conformation, and orientation of the molecule. It allows consideration of electrostatic and other nonsteric factors. To test the model, specific partition functions are derived for several simple geometries describing the membrane and solute. Frequently, the derived expressions agree with past analyses; however, a new expression describing partitioning within an random network of fibers is derived. It agrees with past results only in the limit of low exclusion volumes. With greater volume exclusions, past results greatly overestimate the partition function. It is applied to gel electrophoresis and chromatography and survives testing with available experimental data. Unlike past analyses, it predicts nonlinear Ferguson plots for agarose gel electrophoresis. In addition, an analytical expression predicting the minimum radius of a sphere excluded from a random fiber matrix is derived, tested, and found to agree with experimental data.

Diffusion and interaction in PEG-DA hydrogels

“…Allowing five days of diffusion to reach equilibrium, the difference in the fluorescence intensity to the bulk solution depends on the size of the applied dextran as well as the mesh sizes ξ of the hydrogel ( Figure 1). The relation between the two intensities is given by the partition ratio K. Further information on the network structure of the hydrogels were obtained by analyzing the decay curve of the partition ratios as a function of the radius of the test solutes [21]. Fitting analysis of the obtained data clearly indicate that the partition ratios follow an exponential decay represented by the form…”

“…For A = 1 equation (1) describes the theoretically expected form of the partition ratios of spherical, non-interacting molecules in a network of randomly oriented planes [21]. In this case the factor s represents the mean surface area of the network planes per unit volume (see Appendix).…”

“…Diffusion coefficients were measured using the fluorescence recovery after photobleaching (FRAP) on a setup which has been established for three-dimensional measurements in hydrogel samples. Furthermore, the detailed analysis of the equilibrium partition ratios is fundamental in understanding the physical-chemical nature of the interaction between solutes and polymer [21]. Complementing the FRAP analysis with partitioning analysis provides access to short and long term interactions separately.…”

Characterization of size-exclusion effects in highly swollen hydrogels: Correlation and prediction

“…Models for Size Exclusion Schnitzer's expressions are able to correlate quantitatively data in electrophoresis and size-exclusion chromatography (5). For the distribution of a spherical solute in a randomly-oriented and distributed meshwork of cylindrical fibers, neglecting fiber-end effects, Schnitzer developed the following expression (the SRF model): (2) where u~ is the volume fraction of the gel excluded to a point solute.…”

A major endothelial plasmalemmal sialoglycoprotein, gp60, is immunologically related to glycophorin.

“…Some of these proteins may be involved in a number of important vascular phenomena, including receptor-mediated transcytosis, cellular diapedesis, hemostasis, and blood-borne metastasis (1). The specific binding of albumin to the endothelial surface (2-5) via one of thdse sialoglycoproteins, gp6O (6), as well as two other albumin-binding proteins (7,8), apparently increases capillary wall permselectivity (9) by increasing both charge and volume exclusion within the endothelial glycocalyx (10)(11)(12).…”