Dextran molecules

Classical gene transfer methods still in use today are diethylamino ethyl (DEAE)-dextran and calcium phosphate precipitation, electroporation, and microinjection. Introduced in 1965, DEAE-dextran transfection is one of the oldest gene transfer techniques [2]. It is based on the interaction of positive charges on the DEAE-dextran molecule with the negatively charged backbone of nucleic acids. The DNA-DEAE-dextran complexes appear to adsorb onto cell surfaces and be taken up by endocytosis. 

The most important adverse effect results from the antigenicity of dextrans, which may lead to an anaphylactoid reaction. Dextran antibodies can be intercepted without an immune response by injection of small dextran molecules (MW 1000), thus obviating any incompatibility reaction to subsequent infusion of the dextran plasma substitute solution. 

A series of manganese(II) chelates attached to polysaccharide molecules were synthesized and the Rj values were measured [72]. Ethylenediaminetetraacetic acid (Fig. 2) chelated to manganese(II) and attached to sucrose-epichlorohydrin copolymer and aminoethyldextran yielded Rj values of 19.2 mM s and 12.8 mM s , respectively, at 10 MHz and 37°C in a 1 2.13 glycerol-water mixture. Diethylenetriaminepentaacetic acid (Fig. 2) and triethylenetetraamine-hexaacetic acid (TTHA, Fig. 2) were both conjugated to dextran molecules. Chelating of manganese(II) ions resulted in complexes with Rj values at 10 MHz... 

This xerogel is a polymer of the polysaccharide dex-tran, a naturally derived polymer of glucose produced by cultures of a micro-organism, Leuconostoc mesen-teroides. The gel is formed when the dextran molecules comprising the disperse phase of the hydrocolloid are cross-linked by a chemical process utilizing epichloro-hydrin and sodium hydroxide. Dextranomer is available as beads or paste. The material requires a secondary dressing. 

Dextran injections are sterile solutions of dextran with weight average molecular weights of about 40 000-110 000. Dextrans with a molecular weight of about 50 000 or less are excreted in the urine within 48 hours of injection. Dextran molecules with higher molecular weights disappear more slowly from the bloodstream and are temporarily stored in the reticuloendothelial system. 

Measure the volume of eluent collected to completely remove the blue dextran from the column. This is the void volume of the column, because the blue dextran molecules are too large to be retained. 

Sephadex LH-20 (Pharmacia) is a support for gel chromatography and is widely used in isolation protocols for proanthocyanidins. It is composed of dextran molecules which are three-dimensionally cross-linked with hydroxypropyl groups [205]. Proanthocyanidins are separated by filtration (molecule sieve effect of the gel) and adsorption (hydrogen bonding). Retention increases primarely with increasing ( ) molecular weight and C4—>C6 linked procyanidins are more retarded than their C4—>C8 linked counterparts [206-207]. Sephadex LH-20 has first been used for sample clean up in the analysis of apple ciders by Lea and Timberlake [208]. So far, no pre-packed columns exist on the market. All methods described in the literature work with different column dimensions (see Tab. (6)). Standardization would help to make results more comparable. Some validation procedures have been performed for two protocols [185,209],... 

Cotton linters were swollen to an increasing extent by means of phosphoric acid of increasing concentration, Using a number of simple sugars plus a series of dextran molecules ranging in M.W. from 180 to 2,4 X 107 and diameter from 8 to 1600 A, it was possible to measure the pore volume and calculate the surface area within the swollen fibres accessible to all the molecules within this range. The substrates reacted with a commercial cellulose enzyme preparation, and the initial rate of reaction was compared with the accessibility of the substrate to molecules of various sizes. There was found to be a linear relationship between the initial reaction rate and the surface area within the cellulose gel which was accessible to a molecule of 40 A, diameter. 

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