Sedimentation experiments

If a sedimentation experiment is carried out long enough, a state of equilibrium is eventually reached between sedimentation and diffusion. Under these conditions material will pass through a cross section perpendicular to the radius in both directions at equal rates downward owing to the centrifugal field, and upward owing to the concentration gradient. It is easy to write expressions for the two fluxes which describe this situation ... 

The sedimentation experiments were carried out using an ultracentrifuge. ... 

In a batch sedimentation experiment, the sediment builds up gradually and the solids which are deposited in the early stages are those which are subjected to the compressive forces for the longest period of time. In the continuous thickener, on the other hand, all of the particles are retained for the same length of time with fresh particles continuously being deposited at the top of the sediment and others being removed at the same rate in the underflow, with the inventory thus remaining constant. Residence time distributions are therefore not the same in batch and continuous systems. Therefore, the value of tR calculated from equation 5.59 will be subject to some inaccuracy because of the mismatch between the models for batch and continuous operation. 

The difference is likely to be attributed to the fact that d/d, was very small in the sedimentation experiments. More recently, Khan and Richardson114 have proposed the following relation to account for the effect of the walls of the vessel in fluidisation ... 

Ellis et al. (2003) obtained an Sse(iv)-se(o) range for Se(lV) reduction of 5.5%o to 5.7%o in three experiments with two of the three sediment slurries used for the Se(Vl) reduction experiments reviewed above. Se(lV) concentrations were 100 pmol/L and 240 nmol/L for the estuarine sediment experiments and 460 nmol/L for the wetland sediment. As with the Se(Vl) reduction experiments from this study, there was no apparent dependence on Se concentration or sediment type, though the number of experiments was small. 

EXAMPLE 2.1 Analyzing Cumulative Sedimentation Data for Most Probable Settling Velocity. The following data show—as a function of time—the weight (as percentage of total) of suspended clay particles W, which has accumulated on a plate submerged 20 cm beneath the surface in a sedimentation experiment (Oden 1915). 

The results of a sedimentation experiment in a centrifugal field are conventionally reported in terms of what is known as a sedimentation coefficient. This quantity is defined as... 

Sedimentation. The sedimentation experiments are tabulated in Tables I and II. In Table I typical sedimentation coefficients determined in H20 and D20 are in close agreement here and with previously reported values determined for both protio and deuterio phycocyanin from F. calothricoides (15,16). Each of the tabulated coefficients is for a single experiment at an approximate protein concentration of 15 mg. per ml. Lyophilizing a phycocyanin preparation twice had little effect on the observed sedimentation coefficients. In calculating the S values the same partial specific volume of the protein was used for both D20 and H20. This practice is consistent with the recent results of Edelstein and Schach-man (7). Small increases in sedimentation coefficients from H20 to D20 are to be expected because of deuterium substitution on exchangeable positions. The slope of an S vs. concentration plot for phycocyanin in H20 and D20 would also probably differ. Consequently, small changes in S from H20 to D20 would be expected at a constant protein concentration. 

To substantiate the credibility of the newly developed method, a polydisperse system with f(M) known in advance was subjected to an equilibrium sedimentation experiment. Then the new computation-ori-... 

The equilibrium sedimentation experiment of sample P was analyzed only by applying the computation-oriented expressions. The resulting f(M) was compared with the previously obtained f(M). From the curve of f(M) the average values were computed and compared with the values computed in the same way from individual distribution curves of fractions A, B, and C. These values were also compared with M values obtained in a conventional way from equilibrium sedimentation by applying Equation 2, and with M values determined from velocity sedimentation experiment, Equation 30 (see Table II). 

The second virial coefficient A2 from osmometry, light scattering, and sedimentation experiments were found in the same range, 4-10-10-7 molTg-2 for DADMAC contents 8-100 mol %. The change is mainly influenced by the changes in charge density [46,67,131]. 

Figure 12 Diagram of assembled states of the coat protein of tobacco mosaic virus M free monomers, BD cylindrical disks, LW/H protohelices and helices. Symbols results from differential scanning microscopy DSC, titration, and sedimentation experiments, lines theory. The theory is based on binding energy Equation (9) and presumes competing repulsive Coulomb and attractive hydrophobic interactions (Kegel and van der Schoot, 2006).

Fig. 2 Results of surficial material collected from shallow fjord sediments experiment. Treatment key ArtSW artificial seawater AutoC autoclaved fjord water Ml- 0.8 pm filtered water from mesocosm 1 ( = no nutrients added) M2- 0.8 pm filtered water from mesocosm 2 (N03 and P04 added), (a) Abundance of P. pouchetii colonies (colonies ml-1) histograms represent colony estimates for each replicate bottle, (b) Colony diameter (pm) error bars represent standard deviations of estimates within each bottle calculated from triplicate counts, (c) Cell density (cells colony-1) error bars represent standard deviations of estimates within each bottle calculated from triplicate counts...

There are several requirements that the suspending liquids must satisfy in order to be used for the sedimentation experiments (I) they should be chemically inert with respect to the solid particles (2) the boiling temperature should be reasonably high to minimize evaporation (3) the density of the liquid should be less than that of the particles (4) liquids with zero or nearly zero dipole moment as well as those with higher dipole moment should be used in order to cover a wide polarity range (5) the liquid components should be miscible in all ratios... 

CD spectroscopy has also provided valuable insight into the chemical stability and chemical denaturation of proteins. A recent study by Rumfeldt etal. examines the guanidinium-chloride induced denaturation of mutant copper-zinc superoxide dismutases (SODs). These mutant forms of the Cu, Zn-SOD enzyme are associated with toxic protein aggregation responsible for the pathology of amyotrophic lateral sclerosis. In this study, CD spectroscopy was used in conjunction with tryptophan fluorescence, enzyme activity, and sedimentation experiments to study the mechanism by which the mutated enzyme undergoes chemical denaturation. The authors found that the mutations in the enzyme structure increased the susceptibihty of the enzyme to form partially unfolded destabilized monomers, rather than the stable metaUated monomer intermediate or native metallated dimer. 

There is a substantial literature on the thermodynamics of three-component systems—water, protein, and second solute. For a review of early work, methods, and theory, with emphasis on sedimentation experiments, see Kuntz and Kauzmann (1974). Timasheff and colleagues (see Lee et ai, 1979, and references cited therein) have developed a beautiful formalism for treating the thermodynamic nonideality of three-component systems in terms of the preferential interaction parameter... 

Velocity sedimentation experiments on both proteins at several concentrations were performed at 55,000 rpm in the same buffer at 20°C. The data were analyzed using the time derivative method of Stafford [8]. 

A sedimentation experiment has been established as a commercial apparatus is not available. The sedimentation takes place in the flocculator itself. This way, the floes can be formed under accurately controlled circumstances. 

Acetamide will exist as a vapor in the ambient atmosphere. Atmospheric degradation occurs by reaction with photochemically produced hydroxyl radicals the half-life for this reaction in air is estimated to be 7.6 days. If released to soil, acetamide is expected to have very high mobility and is not expected to adsorb to suspended solids and sediment. Experiments suggest that this chemical may break down in the environment through biodegradation and not through hydrolysis. Volatilization from water surfaces is not expected to be an important fate process based on this compound s estimated Henry s law constant. The potential for bioconcentration in aquatic organisms is low. 

Quartz sandstones are generally expected to remain loose and friable until they have been subjected to a burial depth greater than about 3 km (BJprlykke et al., 1992 Giles et al, 1992 BJprlykke and Ege-berg, 1993) unless the sediments experience very... 

The hydration (or more generally, solvation) of molecules or ions in solution is in many respects not a precisely defined concept. Some molecules of the solvent may be very firmly bound by the solute, so that they accompany it for a long jjeriod during a diffusion or sedimentation experiment, and exchange slowly or not at all with the free solvent molecules in the surrounding medium. Other solvent molecules may be... 

Q.26.12 Identical amounts of thyroxine transport protein (TTR) are placed in water and gasoline. Identical sedimentation experiments are run on both samples. It s discovered tliat TTR sediments faster in water what is a likely explanation of this observation ... 

This process is most important in marine sediments where the pore waters contain appreciable amounts of dissolved sulphate. Bacterial sulphate reduction (BSR) operates when the pore waters are devoid of dissolved oxygen (i.e. anoxic). In euxinic basins the sediment experiences BSR diagenesis directly at the sediment-water interface (Fig. 1) in other words, no oxic and suboxic phases are encountered (Curtis, 1987). Sulphate reduction is aided by anaerobic bacteria, as follows ... 

Electrophoretic studies of the isolated erythrocuprein employing starch or polyacrylamide gels have been carried out by most of the above-cited authors. The homogeneity was not as satisfactory as in the sedimentation experiments a major component and a slightly faster component were always detectable. At the moment it is not known whether there is a genuine second component or whether the erythrocuprein decomposes during the disc-electrophoretic separation. The electrophoretic separation pattern of bovine erythrocuprein is essentially the same for erythrocuprein from human tissues (64, 68). 

Criteria (1) can be evaluated by sedimentation experiments and (2) can be tested by vacuum, pressure filtration, or CSX experiments. Filtration and CSX experiments will be discussed in Section 22.7. 

The presence of two zinc atoms per subunit of LADH was first established by Akeson (134). He also showed that one zinc was essential for activity and suggested that the second zinc may have a structural role. There is no difference in zinc content between the multiple forms of the EE isozymes (164). Attempts to differentiate the function and chemical reactivities of the two zinc atoms have been described in a series of papers (133,165-167) which have been reviewed (168). One zinc atom per subunit could be selectively exchanged and removed by dialysis. The modified enzyme containing one zinc atom per subunit was catalytically inactive and did not bind 1,10-phenanthroline. From this information, combined with the X-ray data which show that the catalytic zinc atom binds 1,10-phenanthroline, it is evident that the catalytic zinc atom is first removed during dialysis under these conditions (167). The second zinc atom can be selectively removed, in preference to the catalytic zinc, by carboxymethylation (165). From sedimentation experiments of zinc-free... 

In a sedimentation experiment, the weight-average molar mass is given by (eqn 19.20)... 

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