Sedimentation equilibrium, determination

The sedimentation velocity determination is dynamic and can be completed in a short period of time. The sedimentation equilibrium method gives quantitative results, but long periods of time are required for centrifugation at relatively low velocities to establish equilibrium between sedimentation and diffusion. 

SEC-MALLS and SEC-LALLS Coupled chromatography and light-scattering photometry that allows the determination of a number of important values along with chain length distribution, sedimentation equilibrium experiment Ultracentrifugation technique that allows chain length information to be determined. 

For a binary polymer solution, the reciprocal of the osmotic compressibility 0n/0c at constant T and the solvent chemical potential p0 can be determined by sedimentation equilibrium through the relation [58,59] ... 

Itou et al. [60] determined 0II/0C for isotropic solutions of poly(n-hexyl isocyanate) (PHIC) and dichloromethane (DCM) from sedimentation equilibrium data on narrow distribution PHIC samples. Figure 3 shows their results, where the ordinate Mw(0II/0c) represents the osmotic pressure increment on the molar concentration scale. 

The determination that the low MW, acetylated aspen lignins examined actually fit universal calibration, however, must be deferred to future studies comparing these data to results from LALLS and sedimentation equilibrium analysis (if possible). 

Recently, efforts have been made to produce calibration standards of higher molecular weight that are chemically similar to lignins, by step-wise syntheses (12), anion-initiated polymerization of quinonemethides (13), and preparative HPSEC of acetylated lignins (14). Knowledge of the molecular weights of these materials is either built into the method of preparation or determined by absolute methods such as sedimentation equilibrium measurements. 

In principle, the nature of biopolymer interactions in solution can also be determined from sedimentation equilibrium of a single biopolymer component at constant temperature T and angular velocity co. The thermodynamic activity on a weight-concentration basis, z, = yiC/M at radial distance r is related to that at a selected reference radial position (r ) by the following formal expression (Deszczynski et al., 2006) ... 

Ill, which had been radioactively labeled by 14C acetylation. Cyto-chrome-c and fluorescein labeled E. coli HPr, a protein of known sequence, have been added to the sample as internal molecular weight standards. The Mapp determined for Factor III by gel permeation in 6M GuHCl, 11,000 300, is in good agreement with the value obtained from sedimentation equilibrium in 6M GuHCl-O.lM 2-mercaptoethanol, 12,000 (20). 

An alternative method sometimes used to determine molecular weights of macromolecules is sedimentation equilibrium. In the previous example, using the Svedberg equation, the sample is rotated at a rate sufficient to sediment the particles. Here, the sample is rotated at a lower rate, and the particles sediment until they reach an equilibrium position at the point where the centrifugal force is equal to the frictional component opposing their movement (see Equation 7.6). The molecular weight is then calculated using Equation 7.12. 

The molecular weight of the calf duodenal adenosine aminohydrolase determined from sedimentation and diffusion data (91) and by comparative elution from Sephadex gels (93, 94) ranges from 31,000-35,000 (84,91, 93, 95). A molecular weight of 52,000 from sedimentation velocity and sedimentation equilibrium data has not been confirmed (93). 

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