Ogston model

Partition coefficients for various gel models are given in Table 3. This table shows the dependence of on the assumed structure of the pores. The Ogston model, for example, gives... 

Johansson and coworkers [182-184] have analyzed polyacrylamide gel structure via several different approaches. They developed an analytical model of the gel structure using a single cylindrical unit cell coupled with a distribution of unit cells. They considered the distribution of unit cells to be of several types, including (1) Ogston distribution, (2) Gaussian distribution of chains, and (3) a fractal network of pores [182-184]. They [183] used the equilibrium partition coefficient... 

Many investigators have used the Ogston model and its fundamental idea as a basis for their models. Most recently, Johansson and Elvingson [182] obtained the probability distribution g(r) for spaces in a random suspension of fibers i.e., the probability that a randomly chosen point in a network of fibers is found at a radial distance r to the fiber of closest approach. For a cylindrical cell (CC) model, which consists of an infinite cylindrical cell, containing solvent and polymer, with the polymer represented as a rod centered in the cell, they obtained g(r) for one cylindrical cell as... 

Amsden [14] used the Ogston model coupled with probability argument to find... 

Morris [250] extended the Ogston model to gel electrophoresis. He found empirically that the product of parameters (/v) for gel filtration was proportional to the total monomer con-... 

The standard Rodbard-Ogston-Morris-Killander [326,327] model of electrophoresis which assumes that u alua = D nlDa is obtained only for special circumstances. See also Locke and Trinh [219] for further discussion of this relationship. With low electric fields the effective mobility equals the volume fraction. However, the dispersion coefficient reduces to the effective diffusion coefficient, as determined by Ryan et al. [337], which reduces to the volume fraction at low gel concentration but is not, in general, equal to the porosity for high gel concentrations. If no electrophoresis occurs, i.e., and Mp equal zero, the results reduce to the analysis of Nozad [264]. If the electrophoretic mobility is assumed to be much larger than the diffusion coefficients, the results reduce to that given by Locke and Carbonell [218]. 

Locke, BR Trinh, SH, When Can the Ogston-Morris-Rodbard-Chrambach Model be Applied to Gel Electrophoresis, Electrophoresis 20, 00, 1999. 

Tietz, D, Evaluation of Mobihty Data Obtained from Gel Electrophoresis Shategies in the Computation of Particle and Gel Properties on the Basis of the Extended Ogston Model, Advances in Electrophoresis 2, 109, 1988. 

The combination of Equations (2) and (3) actually predicts a linear relationship between ln(r) and (p. However, according to the Ogston s model, for a homogeneous gel = kkcC, where is the radius of the polymer chain and c is the polymer chain concentration and a linear relationship is expected between ln(r) and c, too. Similarly, the combination of Equations (2) and (4) predicts a linear relationship also between ln(D) and both (p and c. 

Measured in water (ISEC characterization based on the Ogston s model assumption is not generally reliable in alcohols owing to the occurrence of enthalpic interactions [151]). 

Actually, anyone considering models, as Ogston obviously did, could easily grasp that compound 1 has a mirror image on which it is not superimposable. The reason this had not been grasped was that the wrong answer seemed so totally and obviously right, that no one had felt it was necessary to consult models. 

Figure 9.1 Models for macromolecular electrophoresis. (A) Reptation of long DNA fragments through a polyacrylamide gel. Redrawn from Bloomfield et al. (2000). (B) Ogston sieve model, which applies when Rg of the macromolecule is smaller than the diameter of the pore. (C) Scanning electron micrograph of the interior of a 7.5% (w/v) polyacrylamide gel. Reprinted from Yuan et al. (2006) with permission.

Figure 9.2 Native gel electrophoresis of the Tetrahymena P4—P6 RNA. (A) The folded and extended forms equilibrate rapidly, producing a single band whose mobility reflects the average structure of the RNA. U1, U2, BP5/5a refer to mutations in a hinge region. RNAs were run on native 6% (19 1 monorbis) polyacrylamide gel in TBE + 10 mM MgCl2 at 25 C. (B) Ferguson plot shows that the relative mobility (M) depends linearly on gel concentration, as predicted by the Ogston model. Reprinted from Szewczak and Cech (1997).

Locke, B. R., and Trinh, S. H. (1999). When can the Ogston-Morris-Rodbard-Chrambach model be applied to gel electrophoresis Electrophoresis 20, 3331—3334. 

The classical thermodynamic and kinetic model is that of a rigid sphere impenetrable by water. A spherical geometry has been observed in many polysaccharide systems, notably hyaluronic acid-protein complexes (Ogston and Stainer, 1951), dispersed gum arabic (Whistler, 1993), and spray-dried ungelatinized starch granules (Zhao and Whistler, 1994). Spherulites of short-chain amylose were obtained by precipitation with 30% water-ethanol (Ring et al., 1987), and spherulites of synthetic polymers were obtained... 

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