Sedimentation coefficient-molecular weight

Application of Sedimentation Coefficient Molecular Weight Determination See Eq. (10.21). 

The order q can be positive or negative, as desired. It may be an integer or a fraction and can take real or imaginary values. Consequently, a moment generally is expressed in physical units different from the property. The property may be the degree of polymerization, the molecular weight, the sedimentation coefficient, molecular dimensions, or any other desired property. 

The purity of four isoenzymes of an a-amylase isolated from red spring wheat has been established by chromatography, electrophoresis, and sedimentation studies. The isoenzymes have identical diffusion coefficients, molecular weights [4.51 x 10 (by sedimentation) and 4.20 x 10 (by electrophoresis)], pi values (6.05—6.20), and pH optima (5.6—5.5). The proteins contain relatively large proportions of glutamic and aspartic acids, but no sulphydryl groups. The inhibition of wheat a-amylase by L-ascorbic acid and derivatives of isoalloxazine has been studied. ... 

At first glance, the contents of Chap. 9 read like a catchall for unrelated topics. In it we examine the intrinsic viscosity of polymer solutions, the diffusion coefficient, the sedimentation coefficient, sedimentation equilibrium, and gel permeation chromatography. While all of these techniques can be related in one way or another to the molecular weight of the polymer, the more fundamental unifying principle which connects these topics is their common dependence on the spatial extension of the molecules. The radius of gyration is the parameter of interest in this context, and the intrinsic viscosity in particular can be interpreted to give a value for this important quantity. The experimental techniques discussed in Chap. 9 have been used extensively in the study of biopolymers. 

In a solution of molecules of uniform molecular weight, all particles settle with the same value of v. If diffusion is ignored, a sharp boundary forms between the top portion of the cell, which has been swept free of solute, and the bottom, which still contains solute. Figure 9.13a shows schematically how the concentration profile varies with time under these conditions. It is apparent that the Schlieren optical system described in the last section is ideally suited for measuring the displacement of this boundary with time. Since the velocity of the boundary and that of the particles are the same, the sedimentation coefficient is readily measured. 

Mandelkern and Floryt have assembled the sedimentation coefficients and intrinsic viscosities for polymers of various molecular weights. As shown... 

Fig. 2. Ultracentrifugal pattern for the water-extractable proteins of defatted soybean meal in pH 7.6, 0.5 ionic strength buffer. Numbers above peaks are approximate sedimentation coefficients in Svedberg units, S. Molecular weight ranges for the fractions are 2S, 8,000—50,000 7S, 100,000—180,000 IIS, 300,000—350,000 and 15S, 600,000—700,000 (9). The 15S fraction is a dimer of the IIS protein (10).

Keywords Complex Flexibility Molecular weight distribution Mucoadhesion Sedimentation coefficient distribution... 

Analytical ultracentrifugation (AUC) Molecular weight M, molecular weight distribution, g(M) vs. M, polydispersity, sedimentation coefficient, s, and distribution, g(s) vs. s solution conformation and flexibility. Interaction complex formation phenomena. Molecular charge No columns or membranes required [2]... 

The sedimentation coefficient s°, or its normalized form 5 0 w function of the conformation and flexibility of a macromolecule (via its translational frictional property) and its mass. So if we are going to obtain conformation and flexibility information we need to know the molecular weight (molar mass)... 

It is possible to get molecular weight from the sedimentation coefficient if we assiune a conformation or if we combine with other measurements, namely the translational diffusion coefficient via the Svedberg equation [50]... 

A sedimentation coefficient distribution—either c s) versus 5 or g (s) vs. s—for a polysaccharide can also be converted into an apparent molecular weight distribution if the conformation of the polysaccharide is known or can... 

One can see the M procedure has a parallel to either g (s) vs. s or c(s) vs. s in sedimentation velocity where the data are transformed from radial displacement space [concentration, c(r) versus r] to sedimentation coefficient space [g s) or c(s) versus s]. Here we are transforming the data from concentration space [concentration relative to the meniscus j(r) versus r] to molecular weight space [M r) versus r]. 

The relation finking the sedimentation coefficient with the molecular weight for a homologous polymer series given above is (see [61, 111]) ... 

DNAPLs have higher densities than water, most between 1 and 2 g/mL, some are near 3 g/mL, for example, bromoform, which has a density of 2.89 g/mL. They have limited water solubilities, and are usually found as the free-phase immiscible with water or as residuals trapped by soil. Most DNAPLs are volatile or semivolatile Pankow82 has listed information on their physical and chemical properties, such as molecular weight, density, boiling points, solubility in water, vapor pressure, sediment/water partition coefficient, viscosity, Henry s law constant, and so on (see Tables 18.8 and 18.9). 

Sedimentation coefficients are expressed in Svedbergs (S), after the Swedish biochemist The Svedberg who developed the ultracentrifuge in the 1920s. While S values are indicative of molecular weight, they are not addi-tive-the 70s ribosome is made up of one 50S and one 30S subunit. 

If (1) the diffusion coefficient D of the polymer in the used solvent, (2) the specific volume v of the dissolved polymer, and (3) the density of the solvent solvent known, one can determine the molecular weight of the dissolved polymer according to the above equation by measuring the sedimentation coefficient (by measuring the maximum of the concentration gradient at regular time intervals). 

The thus determined molecular weight is an apparent one since s and D depend on the polymer concentration. Therefore, extrapolation to concentration zero is required. The sedimentation coefficient obtained by extrapolating c —> 0 is called sedimentation constant Sn ... 

Evidence that this is the case has also been obtained from sedimentation velocity studies on dextrans where the sedimentation coefficient S, which is proportional to M/f21, is shown to be molecular weight-independent at high concentrations 15). Furthermore, studies on the intradiffusion of tritiated water (HTO) in dextran solution8) (footnote 2) revealed that the term... 

Conformation in solution is indicated by the way in which the hydro-dynamic properties of the macromolecules change with change in molecular weight. From trends in the intrinsic viscosity, the sedimentation coefficient, or the diffusion constant with molecular weight we can learn something about the conformation of the molecule in solution (19,20). 

The molecular weight Mr of a macromolecule can be calculated from the sedimentation coefficient using the Svedberg equation,... 

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

The molecular weights and sedimentation coefficients of human plasminogen and plas-min (p = 1.40 g cm-3) are as follows ... 

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