Exclusion, steric

In the most straightforward approach to gel electrophoresis, the gel essentially acts as a sieve with a distribution of pore sizes. The connection between this mechanism and this of gel filtration was first made by Morris [106]. This author assumed that the ratio of the electrophoretic mobility in the gel p, relative to the mobility in free solvent Po f, the fractional volume available to the particle in 

Once the linear plot of K, versus R has been determined using standards of known radius and charge, the measure of the retardation coefficient for an unknown partide gives access to its effective radius and to its dfective charge. 

For a spherical particle, S = 4I1(R + r) and V = (4I1/3XR + r) where R is the effective particle radius, and r the fiber radius of the gel. This suggests that the retardation coefficient Kr should scale as 

Note that, in contrast with GPC, migration occurs in a uniform gel phase (there is no equivalent of the interstitial solvent here) so that smaller particles migrate faster. 

Flexible macromolecules such as deimturated proteins or single strand and duplex DNA, are also separated in gel electroidioresis. When the radius of gyration is comparable with the pore size of the gel, the proach 

---

All the problems briefly described above justify the large effort to characterize asphaltenes by techniques seldom found elsewhere in the petroleum industry. One of these is to analyze asphaltenes by steric exclusion... 

D, polarizabihty attraction is almost completely offset by steric exclusion. 

In the case of no steric exclusion of the molecule from parts of the stationary phase, the retention can be described by the enthalpic term alone ... 

Size exclusion HPLC has many other common names, such as gel permeation, gel filtration, steric exclusion, molecular sieve chromatography, or gel chromatography. These names all reflect the theoretical mode of action for this type... 

Anderson, JL Quinn, JA, Restricted Transport in SmaU Pores, a Model for Steric Exclusion and Hindered Particle Motion, Biophysical Journal 14, 130, 1974. 

This paper concerns the main properties of water soluble pectins in sol and gel states. First of all, the methods of purification and characterization are discussed. The method of steric exclusion chromatography equipped with different detectors is demonstrated as the most useful to determine the macromolecular characteristics of these polymers the role of aggregation is pointed out. 

The best way then to characterize the pectins is the steric exclusion chromatography equipped with a multidetection and particularly a light scattering detector [13]. 

With use of a THF/n-Heptane mixture for example, in GPC 2 the hydrodynamic volume of polymer mola ules rich in one monomer component can be much more affected than those rich in the other. Steric exclusion paration can then distinguiA compsitional differences. 

Steric Exclusion Liquid Chromatography of Polymers, edited by Josef Janca... 

Solute Flux Solute partitioning between the upstream polarization layer and the solvent-filled membrane pores can be modeled by considering a spherical solute and a cylindrical pore. The equilibrium partition coefficient 0 (pore/bulk concentration ratio) for steric exclusion (no long-range ionic or other interactions) can be written as... 

J. Janca (Ed.), Steric Exclusion Liquid Oiroaatography of Polymers", Dekker, New York, NY, 1984. 

Regnier, F. E. and Noel, R., Glyceropropylsilane bonded phases in the steric exclusion chromatography of biological macromolecules, ]. Chromatogr. Sci., 14, 316, 1976. 

III PEG MPD Steric exclusion Repulsion from charges To hydrophobic regions Good precipitants stabilizers of native structure at low temp., unfolded structure at high temp. stabilizers and solubilizers of hydrophobic domains in proteins... 

Putting two atoms in the same place (steric exclusion)... 

Similar to nitrogen compounds, electron-rich sulfur compounds, such as the sulfides, with the lone pair of electrons on the sulfur atom, are oxidized to sulfoxides and, further, to sulfones by the H202/titanosilicate sytem (218,232, 233). Table XXXI (232) illustrates typical conversions and product selectivities for various sulfides for the reactions catalyzed by TS-1. Bulky sulfides such as alkyl, phenyl sulfides are relatively unreactive because of their steric exclusion from the pores of TS-1. Diphenyl sulfide could not be oxidized at all. As the diffusivity and, hence, the conversion of the sulfide decreases, the further oxidation of the primary product (sulfoxide) becomes more competitive, leading to increased formation of the corresponding sulfone (Table XXXI) ... 

The measured uptake of CPA and PTA over the three activated carbons [55] is shown in Figure 6.28, and the trends predicted by the RPA model in Figure 6.27 are at least qualitatively observed. However, at high pH, over the two highest-surface-area carbons (CA and KB), uptake is about half of that predicted by the RPA model. The discrepancy was explained [55] by steric exclusion of the large Pt ammine complexes, believed to retain two hydration sheaths [15,19], from the smallest micropores of the high-surface-area activated carbon. 

Unlike the pellicular packings used for ion exchange, the packings used in ion exclusion are derived from totally sulphonated polymeric materials. Separation is dependent upon three different mechanisms Donnan exclusion, steric exclusion and adsorption/partitioning. 

Jakob CA, Burda P, Roth J, Aebi M (1998) Degradation of misfolded endoplasmic reticulum glycoproteins in Saccharomyces cerevisiae is determined by a specific oligosaccharide structure. J Cell Biol 142 1223-1233 Janson LW, Ragsdale K, Luby-Phelps K (1996) Mechanism and size cutoff for steric exclusion from actin-rich cytoplasmic domains. Biophys ) 71 1228-1234 Jeffers M, Taylor GA, Weidner KM, Omura S, Vande Woude GF (1997) Degradation of the Met tyrosine kinase receptor by the ubiquitin-proteasome pathway. Mol Cell Biol 17 799-808... 

The basic retention mechanisms of SEC were presented in Sections 16.3.3 and 16.3.4. These mainly include the steric exclusion of macromolecules from the pores of the column packing controlled... 

Janca, J., Ed., "Steric Exclusion Liquid Chromatography of Polymers", CHROMATOGRAPHIC SCIENCE SERIES, Vo. 25, Marcel Dekker, Inc., N.Y. (1984). 

---