Dextran polymer gels

Equation 16.15 shows that, as expected, the gel phase diffusivity approaches zero as the solute radius approaches the mesh size. In a responsive gel, as sweUing increases in response to environmental changes gel phase diffusivity increases with increasing mesh size. Figure 16.16 shows the effect of competitor concentration on predicted gel phase diffusivity assuming a solute radius of 1.5 nm. Using this example and a dextran polymer gel, it is not possible to achieve a cross-link density sufficient to give a predicted mesh size sufficiently small to prevent gel phase diffusivity. However, as Equation 16.12 does not consider the steric effects of the immobilized receptor experimentally determined gel phase diffiisivities are likely to be lower. 

AA AAm Con A DSS DSS-gel LCST MAPTAC MBA MP MP-gel NIPA ONPG PVMA SSPG Tc TMED acrylic acid acrylamide concanavalin A dextran sulfate sodium gel containing Con A/DSS complex lower critical solution temperature [(methacrylamide)propyl]trimethylammonium chloride /V,/V -methylenebis(acrylamide) a-methyl-D-mannopyranoside gel containing Con A/MP complex /V-isopropylacrylamide O-nitrophenyl-P-D-galactopyranoside poly(vinyl methyl ether) stimulus-sensitive polymer gel transition temperature /V,/V,/V, /V -tetramethylethylenediamine... 

The most commonly used matrices for molecular exclusion chromatography are cross-linked polymer gels, such as agarose, dextran, and polyacrylamide. Since dextran and agarose are biodegradable, they should be stored in the presence of antimicrobial agents. 

However, for membrane applications, where the need to constrain physical dimensions and the mechanical properties required impose limits on the acceptable swelling ratio. Equation 16.1 can be used to predict equilibrium polymer concentration and swelling ratio for a gel with a known cross-link density. Figure 16.10 shows such a prediction for a dextran-based gel with an initial polymer fraction of 0.16 based on a dextran of 500 kDa. Other parameter values are given in Table 16.2. 

Belenkii et al. reported in 1975 (8) the SEC of PVP with unspecified molecular weight using Pharmacia Sephadex G-75 and G-lOO columns and a 0.3% sodium chloride solution as the mobile phase. Deviations from universal calibration behavior were noticed from PVP, dextran, polyethylene oxide (PEG), and polyvinyl alcohol. With the development of the important semirigid polymer gel, Toyo Soda TSK-PW columns for water-soluble polymers, Hashimoto et al. reported in 1978 (9) the SEC of PVP K-30 and K-90 using TSK-PW 3000 and two 5000 columns an 0.08 M Tris-HCl buffer (pH =... 

Kamath, K.R. and K Park, Study on the release of invertase from enzymatically degradable dextran hydrogels. Polymer Gels and Networks, 3 (1995) 243-254. 

Thermally-sensitive hydrogels were also used as dehydration reagents. In this case, the water absorption and desorption is led in the proximity of phase-transition temperature of used gels. Polymer gels based on N-isopropylacrylamide have been used for concentrating albumin, gelatine or dextrane solutions [135]. 

GEL FILTRATION (GEL PERMEATION). Exclusion chromatography, using a polymer gel layer. Gel filtration uses a Dextran-type gel to separate water-soluble species. Gel permeation uses a styrene-divinylbenzene-type gel to separate organic species. 

Schacht, E., Nobels, M., Vansteenkiste, S., Demeester, J., Franssen, J. and Lemahieu, A. (1993) Some Aspects of the Cross-Linking of Gelatin by Dextran Dialdhydes. Polym. Gels Networks, 1, 213-224. 

Fig. 4-2. Scanning electron micrograph of an agarose gel (2%). The while bars represent 500 nm. In Superdex SEC media, the voids surrounding the agarose network skeleton are occupied by covalently linked dextran polymer chains. (Preparation and photo A. Medin, Institute of Biochemistry, Uppsala University, Uppsala, Sweden.)...

Size exclusion was first noted in the late fifties when separations of proteins on columns packed with swollen maize starch were observed (Lindqvist and Storgards, 1955 Lathe and Ruthven, 1956). The run time was typically 48 hr. With the advent of a commercial material for size separation of molecules, a gel of cross-linked dextran, researchers were given a purposely made material for size exclusion, or gel filtration, of solutes as described in the classical work by Porath and Flodin (1959). The material, named Sephadex, was made available commercially by Pharmacia in 1959. This promoted a rapid development of the technique and it was soon applied to the separation of proteins and aqueous polymers. The work by Porath and Flodin promoted Moore (1964) to apply the technique to size separation, gel permeation chromatography of organic molecules on gels of lightly cross-linked polystyrene (i.e., Styragel). 

The GBR resin works well for nonionic and certain ionic polymers such as various native and derivatized starches, including sodium carboxymethylcel-lulose, methylcellulose, dextrans, carrageenans, hydroxypropyl methylcellu-lose, cellulose sulfate, and pullulans. GBR columns can be used in virtually any solvent or mixture of solvents from hexane to 1 M NaOH as long as they are miscible. Using sulfonated PDVB gels, mixtures of methanol and 0.1 M Na acetate will run many polar ionic-type polymers such as poly-2-acrylamido-2-methyl-l-propanesulfonic acid, polystyrene sulfonic acids, and poly aniline/ polystyrene sulfonic acid. Sulfonated columns can also be used with water glacial acetic acid mixtures, typically 90/10 (v/v). Polyacrylic acids run well on sulfonated gels in 0.2 M NaAc, pH 7.75. 

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