Photocross-linking azide

Figure 32 Structures of three common photocross-linking moieties. Benzophenone is photoactivated to a reactive diradical that can relax back to the starting material. Aryl azides and diazirines both irreversibly lose N2 to react through nitrene and carbene species, respectively.

Figure 35 Glycan photocross-linking probes for fluorescent labeling. Photocross-linkers are shown in red and fluorophores are in blue, (a and b) Lactose molecules modified with a benzophenone cross-linker and a functional group that can react through click chemistry. After photocross-linking, the adducts are reacted with an azide or alkyne-functionalized fluorophore to fluorescently label the protein-binding partner, (c) Multivalent mannose or fucose (represented in green) probes bear a benzophenone cross-linker and a Cy3 or Cy5 fluorescent label.

Figure 36 Glycan photocross-linking probes with purification tags. Photocross-linkers are shown in red. (a) Glycan probe utilizing nitrophenyl azide and a digoxigenin tag. (b) Mannoside-based probe bearing a benzophenone and a biotin tag.

Figure 37 Bifunctional photocross-linking affinity purification reagents with cleavable linkers, (a) Diazirine-modified LacNAc probe with a biotin tag and a cleavable acylsulfonamide linker, (b) Aryl azide Le probe with a biotin tag that contains a cleavable disulfide linker.

Other groups that are photosensitive and therefore can be photocross-linked include azide (—N3), carbazide (—CON3), sulfonazide (—SO2N3), diazonium salts (R—N2X), and diazoketones with the group I. 

Most of these azide polymers photocross-link at a faster rate than does poly(vinyl cinnamate), when exposed to light of 260 pm. In addition, they responded well to photosensitization. Also, it was observed [50] that the 4-isomer of azidophthalate shows greater speed increase than does the 3-isomer. In general, the poly(vinyl alcohol) derivatives were reported to exhibit higher cross-linking speeds than do other azide functionalized polymers [176]. 

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