Dextran

Biopolymer homoglycans

Whitish odorless solid

Fixed

Soluble in water

• > 3000 mg · kg -1 ( LD50, rat, oral)
• > 12,000 mg · kg -1 ( LD50, mouse, oral)

Dextrans are high molecular weight, branched, neutral biopolysaccharides serve yeasts and bacteria as reserve materials. Since the polymers consist only of glucose units, they are among the homoglycans. Natural dextrans having molecular masses 10000-50000000 Da. They are produced from sucrose by bacteria of the genus Leuconostoc (L. mesenteroides and L. dextranicum ) by means of enzymes outside of the cells ( extracellular).

Properties and Structure

Dextrans are water soluble, the solubility depends on the molecular mass. Here, highly viscous, slimy liquids form. The colloid osmotic pressure of a six percent aqueous solution of dextrans with a molecular mass of about 75,000 Da corresponds to the blood, which is why it can be used as a blood plasma substitute. Low molecular weight dextrans act as platelet aggregation inhibitors.

Dextrans are highly branched polysaccharides. The glycosidic bond to the neighboring glucose molecules can about 1,6 -, 1,4 - or 1,3 -, rarely happen 1,2-linkage.

Use

Dextrans are used:

• 6- percent solution as a blood plasma substitute. Viscosity and colloid osmotic pressure of this solution correspond to that of blood serum.
• As a carrier in the affinity chromatography
• For the purification of mononuclear cells of the peripheral blood ( PBMC)
• During freeze -drying as a stabilizing additive
• In a modified form in the gel permeation chromatography

Furthermore, they are used in products such as:

• Paints
• Means for ground improvement
• Detergents
• Film
• Cosmetics
• Auxiliaries for the paper and textile manufacturing
• Adhesives and glues

For use in microsurgery

Low molecular weight dextrans used in the surgery, in order to minimize the risk of thrombosis in blood vessels. The antithrombotic effect of the dextrans is based on the increase of osmolarity and the consequent increase of the plasma volume, which reduces the viscosity and increases the flow of blood. Dextrans also reduce the activation of the factor VIII protein ( von Willebrand factor protein) that is necessary for blood clotting. They also have an inhibiting effect on the α2 -antiplasmin, thus activating plasminogen.

The residence time in the body depends on the molar mass. At 40,000 Da dextrans remaining two to four, 70,000 Da four to six hours in the bloodstream. Higher dextrans are paid very poorly by the kidney, which is why they stay much longer in the body. During this time, the thrombolytic properties remain.

Chromatography

Cross-linked dextrans were developed by Jerker Porath in 1957. They are used for gel permeation chromatography (GPC ) is used, since they are arranged with the cross-linking (e.g. with epichlorohydrin ) in a defined three-dimensional network, thereby forming pores. Molecules which are larger than the pores migrate when passing through such a column with the solvent, since they are not incorporated into the pores. Smaller molecules can interact with these and move accordingly slower. Thus, it is possible a separation by size and shape of molecules. Well suited for this is large biomolecules, which can be separated so easily. Further cross-linked dextran is used for immunoprecipitation and the stationary phase in affinity chromatography.

Different dextran derivatives are used in the ion exchange chromatography, such as diethyl aminoethyl dextran ( DEAE- dextran, an anion exchanger ), carboxymethyl -dextran (CM- dextran) and dextran sulphate.

Brand name

Cross-linked dextrans are also known under the trademark Sephadex from Pharmacia. Sephadex is an acronym of separation Pharmacia dextran. Are produced Sephadextypen for the hydrophilic and lipophilic gel chromatography.