Tolylene-2,4-diisocyanate TDIC

11) is a homobifunctional reagent, the two isocyanate groups of which have different reactivities due to the presence of the methyl group. Thus, this reagent can be used both in one-step and two-step procedures (Modesto and Pesce, 1973). 

Other homobifmctional reagents The reagent 4,4 -difluoro-3,3 -dinitrophenyl sulfone (FNPS), represented in Fig. 11.11, 

Diazonium compounds, which are formed from aromatic amines with nitrous acid, may react with proteins by electrophilic substitution of the aromatic amino acid residues. Among these, bis-diazotized benzidine (BDB), o-dianisidine, benzidine-(2,2 or 3,3 )-disulphonic acid have been used extensively for protein conjugation (Kennedy et al., 1976a), but they may inactivate the enzyme or the antibody (coupling occurs mainly via the histidyl and tyrosyl residues). 

Extensive lists of other reagents used for protein-protein coupling have been compiled by Kennedy et al. (1976a). Although for some of these reagents the potential for EIA remains to be established, most are of limited value. 

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Fig. 7. Hydrolysis resistant nucleoside linkages. Fig. 1. The TDIC linkage based on tolylene-2,6-diisocyanate (32). Fig. 2 A ribonucleotide linked to LCAA-CPG via a secondary amino group (35) Fig 3. Nucleoside attachment via a 1,6-bis-methylaminohexane linker (36),...

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