Dextran, Molecular Weight 60,000-90,000

Dextran is a high molecular weight polymer of anhydroglucose. It is composed of approximately 95% α-D-(1-->6) linkages. The remaining a(1-->3) linkages account for the branching of dextran. Conflicting data on the branch lengths implies that the average branch length is less than three glucose units. However, other methods indicate branches of greater than 50 glucose units exist. Native dextran has been found to have a molecular weight in the range of 9 million to 500 million. Lower molecular weight dextrans will exhibit slightly less branching and have a more narrow range of molecular weight distribution. The molecular weight of dextran is measured by one or more of the following methods: low angle laser light scattering, size exclusion chromatography copper-complexation and anthrone reagent colormetric reducing-end sugar determination and/or viscosity. During preparation, fractionation can be accomplished by size exclusion chromatography or ethanol fractionation in which the largest molecular weight dextrans precipitate first.

Dextran solutions have been used as plasma extenders. A 6% dextran (MW ~70,000) solution exerts a colloidal osmotic pressure similar to that of plasma proteins. Dextrans with molecular weights greater than 50,000 tend to slowly diffuse across the capillary wall and are slowly metabolized to glucose. Approximately 50% of infused dextran (MW ~70,000) is excreted unchanged in the urine in 24 hours. Dextran can be used to enhance the precipitation and sensitivity of antibody-antigen complexes in immuno-diffusion applications. Dextran (MW ~80,000) was infused into an immunoelectrophoresis gel at a maximum of 80 mg/mL. Use of dextrans as long and hydrophilic spacer arms improves the performance of immobilized proteins acting on macromolecules.