Carbohydrates cross-linkers

The carbonyl-reactive functional group on these cross-linkers is a hydrazide group that can form hydrazone bonds with aldehyde residues. To utilize this functional group with carbohydrate-containing molecules, the sugars first must be mildly oxidized to contain aldehyde groups by treatment with sodium periodate. Oxidation with this compound will cleave adjacent carbon—carbon bonds that possess hydroxyl groups, as are abundant in polysaccharide molecules (Chapter 1, Sections 2 and 4.4). 

On the other end of the cross-linker, the hydrazide functional group can react with periodate-oxidized carbohydrate molecules to form hydrazone linkages (Chapter 1, Sections 2 and 4.5). Thus, glycoproteins can be targeted specifically at their polysaccharide chains, avoiding cross-linking at active sites which can lead to activity losses (Fig. 167). 

The ethylene diamine—dextran derivative may be used to couple with carboxylate-containing molecules by the carbodiimide reaction, to couple amine-reactive probes, or to further modify using heterobifunctional cross-linkers. The hydrazide—dextran derivative may be used to cross-link aldehyde-containing molecules, such as oxidized carbohydrates or glycoproteins. 

Specific groups involved in covalent immobilization of biomolecules to the surface are very often introduced into the structure of this molecule, especially in oligonucleotides and carbohydrates. Carboxylic and amino functionalities are the modifications most frequently used, although aldehyde, thiol, and oxyamino are useful alternatives. In some cases coupling molecules (cross-linkers) are necessary to increase the affinity (or reactivity) of the interacting groups. 

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