Polymers dextran

Homopolysaccharides are synthesised by relatively few spedfic enzymes and are not constructed from subunits. The commerdally important homo polymer dextran is synthesised extracellularly by the enzyme dextransucrase. In Leuconostoc mesenteroides the enzyme is induced by the substrate sucrose. This is deaved to release free fructose and link the glucose to the redudng end of the acceptor dextran chain, which is bound to the enzyme. The product from this bacterium is composed almost exdusively of... 

Brooks (32) has explained the increase in of normal RBCs in the presence of the neutral polymer dextran on the basis of a reduction in counterion screening. That is, counterions are excluded from the cell surface where a significant fluid volume is occupied by the dextran, thus leading to a reduction in the effective I and a decrease in. Thus, Equation 1 can be written as (33,34)... 

Garozzo et al. injected in a preparative SEC apparatus a polydisperse polymer (dextran) and analyzed the collected fractions by light scattering and by MALDI-TOF.Figure 10.6 shows the MALDI-TOF mass spectrum of two dextran samples obtained by this method. The analysis of the spectra yielded = 50000 for the sample on the left and = 90000 for the sample on the right, and these values compare well with the light scattering values (M = 50000 M = 94000). 

In addition, as a hydrophilic and ftmctionalizable polymer, dextrans are used extensively for surface modification in biosensor fabrication. Dextran layers on sensor chips can effectively minimize nonspecific adsorption of analyte and facilitate surface immobilization of ligand, subsequently increasing the sensitivity of biosensors. 

Monte Carlo simulations (Lai and Binder 1992). Figure 6.11 shows scanning force microscopy images of an end-grafted layer of a water-soluble polymer, dextran, which in water appears as a uniform layer, but, after the addition of a poor solvent, propanol, develops lateral structure (Frazier et al. 1997). As the grafting density is increased yet further the homogeneous, layer structure is expected once again to become stable. 

Figure 12 Chromatogram of non-ionic polymer (dextran with mass-average molecular mass of c. 10000) obtained on TSKgel GMPW (two 600 x 7.5 mm LD. columns) with distilled water at a flow rate of ImLmin and 25°C.

Separation by partition between two immiscible aqueous phases has been successfully applied to a large number of proteins, nucleic acids, and cellular particles such as mitochondria, chloroplasts, membrane vesicles, and whole cells. The phase systems are made up of two different water-soluble polymers, dextran and poly(ethylene glycol), dissolved in water and complemented with suitable buffers, salts, and sucrose. Highly selective adjustment of the distribution process is possible by linking an affinity... 

Fig. 7. Graft polymerization (%) versus reac tion time. Backbone polymer dextran Dl, M 9,000 D2, M 61,000 D3, M 196,000...

In a stirred ultrafiltration cell using a flat UF membrane, an aqueous solution of the polymer Dextran 20 was ultrafiltered. Data were gathered at different values of the water flux, and the solute rejection was measured. Dextran 20 is a linear polymer, and, as the solvent flux was increased, the rejection observed for Dextran 20 decreased. A plot of the solvent flux against the quantity (1 —Robs)/K>bs in a semilogarithmic plot (logarithmic on the abscissa for (1 ilobs)/fiobs) yielded a straight line with a positive slope and an intercept of 0.05 on the abscissa. 

Dogic, Z. Purdy, K. R. et al. (2004). "Isotropic-nematic phase transition in suspensions of filamentous virus and the neutral polymer Dextran." Phys Rev E Stat Nonlin Soft Matter Phys,69(5 Pt 1), 051702. 

Dextran polymers Dextran polymer systems have been designed to deliver colon-specific drugs. The intestinal bacterial population secretes an enzyme dextranase that exhibits high specificity to cleave the glycosidic linkages in dextran. This results in the release of the drug in the colon [68]. 

G. Biopolymere E biopolym res The term b. is used for all polymers occuring in living organisms, such as - proteins, - polysaccharides, nucleic acids or mostly biotechnologi-cally produced polymers (- microbial gums, - sucrose, biotransformation to biopolymers), that have structures and/or properties similar to natural polymers (- dextrans, - levans, - polyhydroxybutyric acid, - polylactic acid, - pullulan, -+xanthan). 

In experiments the double strands of the PEG-PEI diblock-copolymer chain, grafted on the water soluble polymer dextran, i.e. PEG-PEI-dex were encircled by y-CD to give supramolecular network, named double-axle intrusion complex. This network can modulate rheological properties in response to pH changes. The linear bifunctional PEG-PEI diblock copolymer was obtained via a cationic ring opening polymerization of 2-oxazoline, using PEG monotosylate as a macroinitiator. 

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