Coprecipitation defined

The CSN is composed of eight subunits called CSNl to CSN8, which are highly conserved in eukaryotes, although only six of them occur in fission yeast. Two hybrid screens and biochemical methods such as far westerns, pull downs and coprecipitation defined a number of CSN subunit-subunit interactions. Figure 13.1 illustrates known subunit-subunit interactions. Initial insight into the architecture of CSN came from the first 2D electron microscopic analysis of purified CSN from human red blood cells [19] (see also Figure 13.2 below). 

The simplest approach to the collection and subdivision of organic materials in seawater is to use some physical or chemical means of removing one fraction from solution or suspension. The techniques vary, from simple filtration to collect particulate matter, to chemical methods, such as solvent extraction and coprecipitation. With each of these methods, the analyst must know the efficiency of collection and exactly which fraction is being collected. Very often the fraction is defined by the method of collection two methods... 

A limited amount of work has been carried out using zirconium phosphates, compounds with well-defined coagulation and adsorption properties. The efficiency of coprecipitation was about 70% for free amino acids and albumin. 

Other dilute solution properties depend also on LCB. For example, the second virial coefficient (A2) is reduced due to LCB. However, near the Flory 0 temperature, where A2 = 0 for linear polymers, branched polymers are observed to have apparent positive values of A2 [35]. This is now understood to be due to a more important contribution of the third virial coefficient near the 0 point in branched than in linear polymers. As a consequence, the experimental 0 temperature, defined as the temperature where A2 = 0 is lower in branched than in linear polymers [36, 37]. Branched polymers have also been found to have a wider miscibility range than linear polymers [38], As a consequence, high MW highly branched polymers will tend to coprecipitate with lower MW more lightly branched or linear polymers in solvent/non-solvent fractionation experiments. This makes fractionation according to the extent of branching less effective. 

If catalysts are prepared by coprecipitation, the relative solubilities of the precipitates and the possibility for the formation of defined mixed phases are essential. If one of the components is much more soluble than the other, there is a possibility that sequential precipitation occurs. This leads to concentration gradients in the product and less intimate mixing of the components. If this effect is not compensated by adsorption or occlusion of the more soluble component, the precipitation should be carried out at high supersaturation in order to exceed the solubility product for both components simultaneously. Precipitation of the less soluble product will proceed slightly faster, and the initially formed particles can act as nucleation sites for the more soluble precipitate which forms by heterogeneous precipitation. The problem is less crucial if both components form a defined, insoluble species. This is for instance the case for the coprecipitation of nickel and aluminum which can form defined compounds of the hydrotalcite type (see the extensive review by Cavani et al. [9] and the summary by Andrew [10]). 

Two types of precipitate contamination have been defined (7) coprecipitation, in which the main precipitate and the impurity come down together and (2) postprecipitation, in which the main precipitate may be initially pure, but is contaminated by a second substance later. Postprecipitation usually occurs from supersaturated solutions. It is dealt with in Section 8-3 and is not considered further here. 

Chiou and Riegelman defined the term solid dispersion as a dispersion of one or more active ingredients in an inert carrier or matrix at solid state prepared by the melting (fusion), solvent, or melting-solvent method. Dispersions obtained through the fusion process are often called melts, and those obtained by the solvent method are frequently referred to as coprecipitates or coevaporates. Examples include sulfathia-zole-providone (PVP) and reserpine PVP. ... 

Even though the component and size of metals and metal oxide support are defined, the catalytic activity for CO oxidation often markedly changes depending on the contact structure of noble metal particles with the supports. In particular, Pd, Ir, and Au exhibit high catalytic activity when they are deposited on reducible metal oxides by coprecipitation, deposition-precipitation, and grafting. Goulanski has classified supported metal catalysts for low-temperature oxidation into three groups [72], There are three possible active sites metal surfaces with metal oxide as a simple support metal oxide thin layer underneath of which metal particles are buried and the perimeter interfaces around noble metal particles. 

It is relevant that attention should now be drawn to the recent work, by Patterson, Pyke, Reid, Tilley, McAteer, et al. (12-16), who have examined several aspects of the structural and catalytic character of coprecipitated tin-antimony oxides. The structure characterization by Pyke, Reid, and Tilley (12) by X-ray diffraction techniques clearly showed that bulk equilibrium is difficult to establish in this system. This observation alone places some earlier data in a different perspective and implicitly demands a high degree of caution in the interpretation of physical and spectroscopic data recorded from these materials. The phase diagram (Fig. 1) defines the... 

Crystalline substances often form with water molecules located at specific sites in the crystal lattice, which are held in coordination complexes around lattice cations. This type of water is denoted as water of crystallization and is common for inorganic compounds. For example, nickel sulfate forms a well-defined hexahydrate, where the waters of hydration are bound directly to the Ni(II) ion. Extraneous inclusion of water molecules can occur if a coprecipitated cation carries solvation molecules with it. Water also can be incorporated into random pockets as a result of physical entrapment of the mother liquor. Well-defined multiple hydrate species can also form with organic molecules. For example, raffmose forms a pentahydrate. 

Most of the above examples followed the dissolution of arsenic in complex sediment systems amended with scorodite and cultures of iron- or arsenate-respiring bacteria. More work was needed with simpler, defined systems to unravel the biological mechanisms from the adsorptive chemical phenomena. Zobrist et al. (43) studied the reductive dissolution of ferrihydrite that was coprecipitated with arsenate. Sulfurospirillum barnesii was the organism of choice because it respires both Fe(III) and As(V). Washed cell suspensions of S. barnesii simultaneously reduced Fe(III) as well as As(V) (Fig. 9). However, As(III) still had a... 

Hydride generation increases the power of detection of atomic spectrometric methods for the determination of certain elements, and allows their matrix-free determination. However, the technique is prone to a number of systematic errors. First, the hydride-forming elements must be present as inorganic compounds in a well-defined valence state. This may require sample decom x>sition prior to analysis. In water analysis, treatment with H2SO4/H2O2 may be effective [106]. Traces of heavy metals such as Cu" may have a catalytic influence on the formation and dissociation of the hydrides, as investigated by Welz et al. [107] in atomic absorption with quartz cuvettes. These in-terferents can be masked by complexation with tartaric acid or coprecipitated with La(OH>3. Calibration by standard addition is advisable. 

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