Dextran solution properties

What is the minimum degree of polymerization necessary for dextran to exhibit properties characteristic of a typical polymer This question should be resolved by examining the molecular weight dependence of its solution properties, although this may be subject to the limitation that native dextran is not a linear polymer but a branched one. The optical rotation data in Figure 2 demonstrate the transition from oligomer to polymer aroxmd the... 

Amylopectins. — The effects of acrylamide graft copolymerization on the solution properties of amylopectin have been discussed. Amylopectin has been dyed with DyAmyl-L and used in this form as a substrate for the assay of a-amylase. Amylopectin has been treated with isocyanate derivatives of 4-amino-( 1,1-dimethyl ethyl)-3-(methylthio)-l,2,4-triazin-5(4/f)-one ( metribuzin ) or acid chloride derivatives of 2,4-dichlorophenoxyacetic acid ( 2,4-D ) and 2,2-dichloropropionic acid ( dalapon ), to produce controlled-release polymeric pesticide systems. The solvent system utilized for these reactions, a lithium chloride or bromide salt in AW-dimethylacetamide, allows dissolution of the reactant salt and facilitates analysis of the polymer product by such techniques as i.r., U.V., and n.m.r. spectroscopies and gel permeation chromatography. Derivatives of other naturally occurring polysaccharides, including amylopectin, cellulose, chitin, and dextran, were also prepared. 

The effects of acrylamide graft copolymerization on the solution properties of dextran have been described. 

To evaluate the lubricating properties of PLL-g-dex copolymer solutions and compare them with other standard aqueous solutions, including HEPES buffer solution, dextran solutions (dex(5.2)), as well as PLL(20)-g-PEG(5) solutions, coefficient of friction (fi) versus speed plots were acquired under both sliding and mixed sliding/rolling conditions using a pin-on-disk tribometer and MTM, respectively. 

BAS Basedow, A.M. and Ebert, K.H., Production, characterization, and solution properties of dextran fractions of narrow molecrrlar weight distributions, J. Polym. Sci. Polym. Symp., 66, 101, 1979. 

Kutsevol, N. Guenet, J.M. Melnyk, N. Sarazin, D. Rochas C. Solution Properties of Dextran-polyacrylamide Graft Copolymers. Polymer 2006, 47, 2061. 

Dextran, although no longer used as a food ingredient, is the base from which the Sephadex range of biochemical adsorbents is prepared. Dextran solutions can also be used as a plasma substitute, being very poorly antigenic and having the correct physical properties... 

Biopolymer Extraction. Research interests involving new techniques for separation of biochemicals from fermentation broth and cell culture media have increased as biotechnology has grown. Most separation methods are limited to small-scale appHcations but recendy solvent extraction has been studied as a potential technique for continuous and large-scale production and the use of two-phase aqueous systems has received increasing attention (259). A range of enzymes have favorable partition properties in a system based on a PGE—dextran—salt solution (97) ... 

Works where study the hydrodynamic properties of a biopolymers in aqueous solution at different temperatures are made by Guner (1999), and Guner Kibarer (2001) for dextran Ghen Tsaih (1998) and Kasaii (2008) for chitosan, Bohidar for gelatin (1998), and Monkos for serum proteins (1996,1997,1999, 2000, 2004 and 2005). 

D protein arrays based on biotin-streptavidin architectures are likely to be the system of choice due to their ease in handling, excellent signal-to-noise ratio and non-specific interactions. 3D surfaces based on porous gold, sol-gel materials, polymer brushes and dextran surfaces are widely used to mimic the properties of bulk solution and increase the immobilization capacity of proteins. 

Adsorbents for biomacromolecules such as proteins have special properties. First, they need to have large pore sizes. A ratio of pore radius to molecule radius larger than 5 is desirable to prevent excessive diffusional hindrance (see Intraparticle Mass Transfer in this section). Thus, for typical proteins, pore radii need to be in excess of 10-15 nm. Second, functional groups for interactions with the protein are usually attached to the adsorbent backbone via a spacer arm to provide accessibility. Third, adsorbents based on hydrophilic structures are preferred to limit nonspecific interactions with the adsorbent backbone and prevent global unfolding or denaturation of the protein. Thus, if hydrophobic supports are used, their surfaces are usually rendered hydrophilic by incorporating hydrophilic coatings such as dextran or polyvinyl alcohol. Finally, materials stable in sodium hydroxide solutions (used for clean-in-place) are... 

The formation of two aqueous phases can be exploited in the recovery of proteins using liquid-liquid extraction techniques. Many factors contribute to the distribution of a protein between the two phases. Smaller solutes, such as amino acids, partition almost equally between the two phases, whereas larger proteins are more unevenly distributed. This effect becomes more pronounced as protein size increases. Increasing the polymer molecular weight in one phase decreases partitioning of the protein to that phase. The variation in surface properties between different proteins can be exploited to improve selectivity and yield. The use of more hydrophobic polymer systems, such as fatty acid esters of PEG added to the PEG phase, favors the distribution of more hydrophobic proteins to this phase. In Fig. 10.13, partition coefficients for several proteins in a dextran-PEG system are given [27]. 

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