Limiting sedimentation coefficient

Since the theories for the interpretation of sedimentation velocity experiments require the sedimentation coefficient at zero concentration, a series of experiments is performed at different concentrations. The value at zero concentration (or limiting sedimentation coefficient ), s[Pg.70]

The fluid resistance experienced by a macromolecular solute moving in dilute solution depends on the shape and size of the molecule. A number of physical quantities have been introduced to express this. Typical ones are intrinsic viscosity [ry], limiting sedimentation coefficient s0, and limiting diffusion coefficient D0. The first is related to the rotation of the solute, while the last two are concerned with the translational motion of the solute. A wealth of theoretical and experimental information about these hydrodynamic quantities is already available for randomly coiled chains (40, 60). However, the corresponding information on non-randomly coiled polymers is as yet rather limited in number and in variety. 

Fig. 25. Molecular-weight dependence of limiting sedimentation coefficient (81) and diffusion coefficient (50) for PBLG in DMF...

Closely connected with the conformational dimensions of the polymer coil, and therefore with the limiting viscosity number, are some other macroscopic quantities, viz. the limiting sedimentation coefficient and the limiting diffusivity. 

Extrapolation of the s-value to zero concentration gives the limiting sedimentation coefficient ... 

This limiting sedimentation coefficient is like [77] an important polymer property. The temperature dependence may be approximated by the expression... 

Estimate the limiting diffusion coefficient, the limiting sedimentation coefficient and the radius of gyration of poly(methyl methacrylate) (M = 2.5 x 105) in toluene. 

In Chap. 9 the limiting sedimentation coefficient s0 and the limiting diffusion coefficient D0 have been discussed. These are the values of the sedimentation coefficient s and the diffusion coefficient D, extrapolated to zero concentration. 

In the definition, v is the velocity of sedimentation and a is the acceleration of free fall or centrifugation. The symbol for a limiting sedimentation coefficient is [s], for a reduced sedimentation coefficient 5°, and for a reduced limiting sedimentation coefficient [s°] see [l.e] for further details. 

Sedimentation The settling of suspended particles or droplets due to gravity or an applied centrifugal field. The sedimentation rate (or velocity) divided by acceleration is termed the sedimentation coefficient. The sedimentation coefficient extrapolated to zero concentration of sedimenting species is termed the limiting sedimentation coefficient. The sedimentation coefficient reduced to standard temperature and solvent is termed the reduced sedimentation coefficient. If the sedimentation coefficient is... 

Recently, we have carried out a series of studies of the hydrodynamic properties of solutions of proteoglycan species Isolated from bovine nasal septum ". We reported a limiting sedimentation coefficient, S° = 23.4S, diffusion coefficient D° =... 

Miscellaneous With certain assumptions it is possible to determine the molar mass fix)m a combination of the intrinsic viscosity [ ] and the limiting sedimentation coefficient sq. In this way, Mandelkem and Flory (128) and Wales and Van Holde (134) derived an expression. An... 

Examples of the relationship between the observed sedimentation coefficient and the polyion concentration are shown in Figure 1. The limiting sedimentation coefficient, ( Sp)y, is observed to depend upon the ionic strength. These differences in (S X are to be expected because of the expansion of the poly ion coil as the ionic strength is decreased, and also because the ionic atmosphere influences the motion of the polyion. 

There have been some reports that the limiting sedimentation coefficient is independent of ionic strength. These results would be obtained if the molecular weights of the samples used in the studies are low or the backbone of the samples is stiff, so that the polyion coil may be free-draining for solvent. 

Experimentally, 5 at a given initial polymer concentration Cb is usually determined by the peak method in which the peak position Tp (the radial distance from the rotation axis) in a concentration gradient (Schlieren) curve is measured as a function of ultracentrifugation time t and then use is made of a plot of In Vp versus co t (according to the relation In rp = scu t + constant) to obtain 5 from the slope. The 5 thus determined is extrapolated to infinite dilution according to the empirical equation 5" = 5o" (l + fesCo + ) to evaluate the limiting sedimentation coefficient So, where fej is a constant independent of Cq. At infinite dilution, 3 equals the translational friction coefficient So (for a polymer molecule), which is related to the hydrodynamic radius Rh by the Stokes relation... 

---