Dialysis, purification

Table 3 Recovery rates of the sodium cations with different analytical methods before and after dialysis purification...

After preparation, colloidal suspensions usually need to undergo purification procedures before detailed studies can be carried out. A common technique for charged particles (typically in aqueous suspension) is dialysis, to deal witli ionic impurities and small solutes. More extensive deionization can be achieved using ion exchange resins. 

Molecular Weight. Measurement of intrinsic viscosity in water is the most commonly used method to determine the molecular weight of poly(ethylene oxide) resins. However, there are several problems associated with these measurements (86,87). The dissolved polymer is susceptible to oxidative and shear degradation, which is accelerated by filtration or dialysis. If the solution is purified by centrifiigation, precipitation of the highest molecular weight polymers can occur and the presence of residual catalyst by-products, which remain as dispersed, insoluble soHds, further compHcates purification. 

Until the early 1960s, laboratory iavestigators rehed on dialysis for the separation, concentration, and purification of a wide variety of biologic fluids. Examples iaclude removal of a buffer from a proteia solution or concentrating a polypeptide with hyperosmotic dialysate. Speciali2ed fixtures were sometimes employed alternatively, dialysis tubes, ie, cylinders of membrane about the si2e of a test tube and sealed at both ends, were simply suspended ia a dialysate bath. In recent years, dialysis as a laboratory operation has been replaced largely by ultrafiltration and diafiltration. 

Water soluble protein with a relative molecular mass of ca. 32600, which particularly contains copper and zinc bound like chelate (ca. 4 gram atoms) and has superoxide-dismutase-activity. It is isolated from bovine liver or from hemolyzed, plasma free erythrocytes obtained from bovine blood. Purification by manyfold fractionated precipitation and solvolyse methods and definitive separation of the residual foreign proteins by denaturizing heating of the orgotein concentrate in buffer solution to ca. 65-70 C and gel filtration and/or dialysis. 

The protein was purified by a dialysis procedure, denatured and analysed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Western blotting indicated that the protein of interest consisted of two components, one of which increased in concentration as the purification proceeded. The authors initially suggested that this could be due to the presence of a number of species produced by modification of the amino acid side-chains, for example, by glyco-sylation, or by modification of the C- or N- terminus. 

Effect of dialysis Stem juice dialysed against distilled water for 16 hours. PG inhibitor activity was examined in the dialysate after 16 hours after removal of precipitate by centrifugation. Table 4 shows that the inhibitor is more or less non-dialysable although a part of its activity is lost during dialysis. Dialysis results in about 3 fold purification of the inhibitor. Dialysed inhibitor was used in subsquent studies. 

Purify the sulfhydryl-modified protein by dialysis against 50mM sodium phosphate, 1 mM EDTA, pH 7.5, or by gel filtration on a Sephadex G-25 column using the same buffer. Again, if a peptide of low molecular weight is being modified, use careful gel filtration for purification. 

Purify the modified protein from reaction by-products by dialysis or gel filtration using 50 mM sodium phosphate, 0.15 M NaCl, 10 mM EDTA, pH 7.2. Alternatively, centrifugal spin columns containing a desalting resin may be used for rapid purification (Thermo Fisher). 

Liposomes containing PE lipid components may be activated with these crosslinkers to contain iodoacetyl derivatives on their surface (Figure 22.29). The reaction conditions described in Chapter 5, Section 1.5 may be used, substituting a liposome suspension for the initial protein being modified in that protocol. The derivatives are stable enough in aqueous solution to allow purification of the modified vesicles from excess reagent (by dialysis or gel filtration) without... 

Van Koten and Frey used a hyperbranched poly(triallylsilane) as the support for palladium- pincer complexes.[63] The supported palladium-pincer complexes were applied in the catalytic aldol condensation of benzaldehyde and methyl isocyanate. Their activity was similar to that of single site Pd catalysts. According to the authors, the complex is suitable for continuous membrane applications, as demonstrated by their purification by means of dialysis. 

Pancreatic amylase is very labile and sensitive to its chemical environment. Its lability is accelerated by purification and by such factors as dilution of its aqueous solutions, dialysis of its aqueous solutions against water, unfavorable hydrogen ion activities and unfavorable temperatures.29-31, 36,33 The loss of amylase activity in solutions of pancreatic amylase increases with increasing temperature and is very rapid between 50° and 60°. The inactivation of pancreatic amylase in aqueous solution may be retarded by the addition of certain anions, of which the chloride ion is outstanding 37-39 by the addition of certain cations, of which... 

Purification is often required for the beads obtained by the techniques described above since undesired substances such as surfactants, coupling agents, etc. need to be removed. This is also valid for dye molecules noncovalently adsorbed on the surface of the beads since they usually have different properties (sensitivity, cross-talk to other analytes, leaching, etc.) compared to the molecules located in the core. The dye-doped beads can be purified by repeated precipitation which is achieved by adding salts (typically sodium chloride). In certain cases (typically for large beads) the addition of salts is not necessary so that the beads can be isolated by centrifugation. Washing with ethanol often helps remove lipophilic dye molecules adsorbed on the surface provided that the polymer is not swellable. Alternatively, dialysis can be useful especially if a hydrophilic water-soluble indicator is covalently coupled to the bead surface. 

---