Trifunctional cross-linking reagents

The sol-gel synthesis of hybrid organic-inorganic compounds usually involves a mixture of di- or trifunctional organosilanes, which introduce Si-C bonds, with metal alkoxides, mainly Si(OR)4, as cross-linking reagents to build the inorganic network. 

Alley, S.C., Ishmael, F.T., Jones, A.D., and Benkovic, S.J. (2000) Mapping protein-protein interactions in the bacteriophage T4 DNA polymerase holoenzyme using a novel trifunctional photo-cross-linking and affinity reagent./. Am. Chem. Soc. 122, 6126-6127. 

One way of obtaining the more useful cross-linked polyurethanes is by using a trifunctional reagent. Thus either the TDI can react with a triol or the propylene oxide can be polymerized in the presence of a triol. Then the isocyanate-alcohol reaction would of course give a cross-linked urethane. 

Figure 193 The trifunctional reagent sulfo-SBED reacts with amine-containing molecules via its NHS ester side chain. Subsequent exposure to UV light can cause cross-link formation with a second interacting molecule. The biotin portion provides purification or labeling capability using avidin or streptavidin reagents. The disulfide bond on the NHS ester arm provides cleavability using disulfide reductants.

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