Stokes radius values

The Kq has been measured directly for Na+ + [222] as counterion in THF, and calculated from the interionlc distance a according to the Fuoss equation for other cryptatee, using the Stokes radius values R8+ obtained from conductimetric studies of the corresponding tetraphenylborides (24). The value of Kq for Na+ + [222] in THP was deduced from that found in THF assuming that the interionlc distance remains constant in both solvents. 

FIGURE 2.8 Determination of relative clearance of dextran as a function of solute size. Please note that Stokes radius (left curve) will yield too low a value for the renal clearance barrier. [Reproduced from Hagel et al. (1993), with permission.]... 

That is, nonionic surfactants caused an increase in the Stokes radius (R) of the particles due to penetration of the phospholipid surface layer and unfolding of apoprotein B molecules leading to particle assymetry at molar ratios of surfactant LDL2 of ca. 1000/1. At higher molar ratios, corresponding to 1-2 moles surfactant per mole of phospholipid, ionic surfactants and nonionics with HLB values < 14.6 caused rapid decreases in the Stokes radius due to breakdown of LDL2 into the lipid surfactant and protein surfactant micelles. 

Stokes radius of a polymer segment = r8. Applying our experimental data to Equation 2, we obtained r8 10 A. This value seems to be quite reasonable. On the other hand, we can set D8 in relation to experimentally determined diffusion constants of a certain polymer. This enables us to attribute a molecular weight of the segment to D8. For MMA, we obtain M , Mma 2000. 

Because the radius of a nonspherical molecule cannot be defined precisely, molecular friction coefficients and diffusion coefficients are often related to the Stokes radius (or Stokes diameter). This is defined as the radius (or diameter) of a sphere having / and D values identical to those of the molecule under consideration. 

The deoxycholate-solubilized squalene synthetase was also chromatographed on Sephadex G-200 and a Stokes radius of 40 A was found for the enzyme. Again, the two catalytic activities were not resolved [72]. This value, along with the 20,w indicated a molecular weight of 55 000 for the protein(s). This contrasts with much higher values reported earlier. Inclusion of certain phospholipids in the tubes used... 

If particles are known to be spherical in shape and nondeformable in the relatively weak flow fields associated with Brownian motion (this may be expected in the case of synthetic latex particles, many proteins, and viruses and probably also holds for certain emulsion particles with rigid ordered interfaces, the Stokes radius will closely correspond to the hard sphere radius R, related to Rg through Rg = 3/5 R and may also be similar to that observed in the electron microscope Rem. The value of Rg should, however, on detailed inspection be greater than the radii measured by the latter methods because it includes bound solvent molecules. The discrepancy can be used to estimate the degree of solvation 81 grams solvent/gram of the particle through the relation ... 

The use of two gel types in gel filtration chromatography to evaluate the molecular weight of proteins is valuable because the measured values of M will differ for the two gels if the protein violates the Kav versus logM relationship. The actual dependence in gel filtration chromatography of proteins is Kav versus log r (Stokes radius) (Siegel and Monty, 1966). 

Figure 15. Relationship between the Stokes radius and the number of amino groups succinylated in bovine serum albumin. O, Values obtained from a calibrated Sephadex G-200 column x, values calculated from diffusion coefficient determined with the ultracentrifuge. From Habeeb ( 1967a ).

Obviously, all of the proposed relationships discussed so far are linear. However, there are also very clear examples where a strong linear relationship was not so obvious, at least not for the total range of w values of the microemulsions studied by different workers. Zulauf and Eicke [76] clearly showed from photon correlation spectroscopy curvilinear relationships between w (up to 50) and the Stokes radius of the water pool in the system AOT/isooctane /H2O (Fig. 3.11). The curves, however, could be divided into linear parts with different slopes. Similarly, acoustic spectroscopic studies of the system A0T/heptane/H20 by Wines et al. [ 152] exhibited a non-linear relationship between the mean diameter of water droplets (from about 8 nm to 17 nm) and the w value (10 to 60) there was no appreciable change from w = 10 to w = 20, but this part of the curve could be taken as linear with a very gentle slope (Fig. 3.12). In the system AOT/isooctane/ H2O, Chen et al. [153] found a linear relationship only up to w = 10. 

Figure 3.11. Relationship between the Stokes radius and the w value for three temperatures, as obtained in the system AOT/isooctane/water. Reprinted with permission from Zulauf and Eicke [76], Copyright (1979) American Chemical Society.

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