Covalent nitrene

The third class of compounds to be discussed in this chapter are those in which an RE group (E = S, Se, Te) is attached to a nitrogen centre. This category includes amines of the type (REfsN and the related radicals [(RE)2N] , as well as organochalcogen(ir) azides, REN3, and nitrenes REN (E = S, Se). Covalent azides of the type RTe(N3)3 and R2Te(N3)2, in which the chalcogen is in the +4 oxidation state, have also been characterized. 

A photoreactive nucleotide, 8-bromo-2 -deoxy-adenosine, was incorporated post-synthetically into a DNA sequence (35, Fig. 13) within the previously determined DNA contact site for the transcription factor. Upon irradiation the resulting nitrene cross-linked primarily to the 50-kDa subunit and covalently modified Lys-244. On the other hand, that amino acid residue appeared not... 

Fig. 5.8 Examples of polymers grafted from nanocarbons, (a) An ATRP initiator covalently attached to RGO via nitrene and carbodiimide chemistry was used for the growth of poly(2-(ethyl (phenyl)amino)ethyl-methacrylate). (b) A RAFT chain transfer agent is covalently attached to GO prior to polymerization of vinylcarbozole.

Accordingly, many reactions can be performed on the sidewalls of the CNTs, such as halogenation, hydrogenation, radical, electrophilic and nucleophilic additions, and so on [25, 37, 39, 42-44]. Exhaustively explored examples are the nitrene cycloaddition, the 1,3-dipolar cycloaddition reaction (with azomethinylides), radical additions using diazonium salts or radical addition of aromatic/phenyl primary amines. The aryl diazonium reduction can be performed by electrochemical means by forming a phenyl radical (by the extrusion of N2) that couples to a double bond [44]. Similarly, electrochemical oxidation of aromatic or aliphatic primary amines yields an amine radical that can be added to the double bond on the carbon surface. The direct covalent attachment of functional moieties to the sidewalls strongly enhances the solubility of the nanotubes in solvents and can also be tailored for different... 

Figure 16. Crosslinking reactions in bisarylazide-rubber resists. The primary photoevent is production of a nitrene which then undergoes a variety of reactions that result in covalent, polymer-polymer linkages. A schematic representation of crosslinking via nitrene insertion to form aziridine linkages is shown together with several other reaction modes available to the...

Specific examples of the classes of carbenes and nitrenes useful for pho-toaffinity labeling are given in Chapter 3. Covalent bonds to biological molecules have also been formed in reactions with free radicals and excited states. As these species are used more rarely their chemistry is outlined in this chapter only. 

The chemistry of covalent azides is primarily determined by the exceptional weakness of the RN—N2 bond they most readily decompose to yield N2 and RN (nitrenes). Table 7 records the bond... 

Arylation or alkylation are used for activation of support and linking of a protein ligand. In such reactions, the functional group on the carrier combines with an NH2 group of the protein (e.g., by 3-fluoro-4,6-dinitrophenyl group or 2-4 dichloro-5-triazine). In this approach, a chloro-5-triazine is coupled to an arylazide. The azide is converted to a nitrene, which upon activation by light reacts with a polymer carrier to form a covalent bond. The chlorotriazine then couples with the protein. 

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