Dextran, crosslinked

In order to minimize the reduction of porosity of polyacrylamide during activation the copolymers of agarose and polyacrylamide are produced. This support combines the advantages of each individual polymer, whilst extending the potential range of derivatisation procedures by virtue of the availability of both amide and hydroxyl groups of activation [81]. Copolymers are produced by LKB-Produkter AB (Bromma, Sweden). A support of similar properties, dextran crosslinked with iV,fV -methylene-bisacrylamide [82], is produced by Pharmacia (Uppsala, Sweden, under the trademark Sephacryl). 

A suitable degree of esterification of dextran with butyric or palmitic acid is achieved by CDI in formamide or DMSO. In the absence of carboxylic acids dextran can be converted by CDI into a crosslinked product with intrachain as well as interchain carbonate links. Such carbonate links permit drugs containing hydroxyl groups to be coupled to the dextran.[174]... 

Addition of an aqueous solution of PEG to a saturated aqueous solution of a-CD at room temperature did not lead to complex formation unless the average molecular weight of PEG exceeded 200 [46]. Moreover, carbohydrate polymers such as dextran and pullulan failed to precipitate complexes with PEG, and the same was true for amylose, glucose, methyl glucose, maltose, maltotriose, cyclodextrin derivatives, such as glucosyl-a-CD and maltosyl-a-CD, and water-soluble polymers of a-CD crosslinked by epichlorohydrin. These facts suggested to Harada et al. the direction for further research. 

A second method of immunotoxin preparation by reductive amination involves the use a polysaccharide spacer. Soluble dextran may be oxidized with periodate to form a multifunctional crosslinking polymer. Reaction with antibodies and cytotoxic molecules in the presence of a reducing agent forms multivalent immunotoxin conjugates. The following sections discuss these options. 

Figure 25.13 Polyaldehyde dextran may be used as a multifunctional crosslinking agent for the coupling of amine-containing molecules. Reductive amination creates secondary amine or tertiary amine linkages.

Dextran derivatives containing carboxyl- or amine-terminal spacer arms may be prepared by a number of techniques. These derivatives are useful for coupling amine- or carboxylate-containing molecules through a carbodiimide-mediated reaction to form an amide bond (Chapter 3, Section 1). Amine-terminal spacers also can be used to create secondary reactive groups by modification with a heterobifunctional crosslinking agent (Chapter 5). 

This type of modification process has been used to form sulfhydryl-reactive dextran polymers by coupling amine spacers with crosslinkers containing an amine reactive end and a thiol-reactive end (Brunswick et al., 1988 Noguchi et al., 1992). The result was a multivalent sulfhydryl-reactive dextran derivative that could couple numerous sulfhydryl-containing molecules per polymer chain. 

The ethylene diamine-dextran derivative may be used for the coupling of carboxylate-contain-ing molecules by the carbodiimide reaction, for the coupling of amine-reactive probes, or to modify further using heterobifunctional crosslinkers. The hydrazide-dextran derivative may be used to crosslink aldehyde-containing molecules, such as oxidized carbohydrates or glycoproteins. 

The crosslinking of polymers in a binary membrane complex via covalent binding is a traditional method for improving the impact resistance of materials. Generally, high molecular crosslinkers have been successful (e.g., dextran dialdehyde... 

The separation of macromolecules on the insoluble, crosslinked porous media was attempted by several researchers just after the World War II. However, the first successful separation of proteins on the crosslinked dextran in aqueous eluents was reported by Porath and Flodin [89] as late as in 1959. Independently, Moore [90] separated the dissolved polystyrenes according to their molar masses on the porous crosslinked polystyrene beads, the raw material for the ion exchangers, in 1964. Above researchers are considered the founders of SEC. 

Sephadex, which can also be obtained in a variety of ion-exchange forms (see Table 15) consists of beads of a crosslinked dextran gel which swells in water and aqueous salt solutions. The smaller the bead size the higher the resolution that is possible but the slower the flow rate. Typical applications of Sephadex gels are the fractionation of mixtures of polypeptides, proteins, nucleic acids, polysaccharides and for desalting solutions. 

Antigens and their corresponding antibodies precipitate by cross-linking to form an insoluble network. Polysaccharides have multiple, repetitive immunodeterminants and virtually none have demonstrable tertiary structure in solution (except, perhaps, under viscous stress). The number of these immunodeterminant groupings on each macromolecule is large. In the case of dextran, for instance, there are several thousand of them (if the dextran has a molecular weight of several million), even if the determinant involves the hep-tasaccharide. There is, thus, ample opportunity to form a precipitating, crosslinked complex with divalent (or polyvalent) antibody molecules. 

B. Preparations after crosslinking the surface proteins with dextran aminophenyldiazotate... 

Dextran gels used as molecular sieves are formed by crosslinking dextrans with epichlorhydrin to give a semisynthetic polysaccharide with a well-defined pore size (Sephadex ). 

Crosslinking or entrapment Entrapment in dextran matrix, polyacrylamide or DNA crosslinked by using some agents such as glutar aldehyde [43] ... 

We have found that crosslinked dextran gel spheres (9) provide a useful model system with which to study agglutination. 

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