Polyethylene glycol Fractionation

A prehminary study of the use of larch AGs in aqueous two-phase systems [394] revealed that this polysaccharide provides a low-cost alternative to fractionated dextrans for use in aqueous two-phase, two-polymer systems with polyethylene glycol (PEG). The narrow molecular-weight distribution (Mw/Mn of 1-2) and low viscosity at high concentration of AG can be exploited for reproducible separations of proteins under a variety of conditions. The AG/PEG systems were used with success for batch extractive bioconversions of cornstarch to cyclodextrin and glucose. 

Water-soluble polymers and polyelectrolytes (e.g., polyethylene glycol, polyethylene imine polyacrylic acid) have been used successfully in protein precipitations, and there has been some success in affinity precipitations wherein appropriate ligands attached to polymers can couple with the target proteins to enhance their aggregation. Protein precipitation can also be achieved by using pH at ustment, since proteins generally exhibit their lowest solubility at their isoelectric point. Temperature variations at constant salt concentration allow for fractional precipitation of proteins. 

Every peak was uniform with respect to m, but each one had a distribution in block length with respect to the PEO blocks (n). To identify fractions, they were collected and subjected to mass spectrometry. The first fraction contained polyethylene glycol and block oligomers with a degree of polymerization m(PO) 1-3. The second fraction was homogeneous with respect to PO and contained m(PO) 4, while fraction 3 resulted from m(PO) = 5. 

Some separation techniques rely on the physical removal of one of the fractions charcoal will strongly adsorb the free fraction allowing its ready removal by centrifugation the addition of dextran reduces the tendency of charcoal to strip bound antigen from the complex alternatively, the bound fraction may be precipitated by the addition of suitable concentrations of various protein precipitants such as alcohol, ammonium sulphate and polyethylene glycol (PEG). 

Under a protective nitrogen blanket, the step 1 product was coupled with methoxy polyethylene glycol prepolymers (Mn 1820 and 4740 Da) using 1,3-dicyclohexylcarbodiimide dissolved in 2 1 . The product was isolated after being purified by precipitation and fractionation from mixed solvents of chloroform/diethyl ether or methanol/diethyl ether. 

Other conventional methods of protein purification also have their place. Precipitation techniques, such as ammonium sulfate or polyethylene glycol fractionation, do not give a high degree of purity on their own but do concentrate the protein and in combination with other techniques, such as ion-exchange chromatography, can be very useful. Separation on the basis of size is not a high capacity technique but can be applicable in the purification of IgM, which,... 

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