Biomolecules functional groups

Thiols (R—S—H) and sulfides (R—S—R ) are sulfur analogs of alcohols and ethers, respectively. Both functional groups are found in various biomolecules, although not as commonly as their oxygen-containing relatives. 

Recent developments in DNA/RNA chemical synthesis have allowed us to attach some functional groups covalently to nucleic acids, thus permitting the introduction of a functionality or properties not normally present in the native biomolecule The use of non-nucleosidic linkers is probably the most popular approach for the 5 -terminal modification of chemically synthesized nucleic acid oligonucleotides and a number of such linkers are commercially available. The linker shown in Fig. 2 is designed as a phosphoramidate derivative so that it can be incorporated into the 5 -terminus of the sequence as the last... 

Important criteria for biomolecule immobilization are high functionality of the chip surface high immobilization capacity optimized density of functional groups stable linkage between the biomolecule and the solid support good accessibility for the interacting molecules low non-specific binding. 

The following sections briefly describe three cycloaddition reactions that can be used to form bioconjugates. These reactions represent highly specific reactant pairs that have a chemoselec-tive nature, meaning they mainly react with each other and not other functional groups, such as those found on biomolecules. For a complete discussion of chemoselective ligation reactions, see Chapter 17. 

The following sections discuss some of the more common biotinylation reagents available for modification of proteins and other biomolecules. Each biotin derivative contains a reactive portion (or can be made to contain a reactive group) that is specific for coupling to a particular functional group on another molecule. Careful choice of the correct biotinylation reagent can result in directed modification away from active centers or binding sites, and thus preserve the activity of the modified molecule. 

Many particle types contain functional groups that are built into the polymer backbone and displayed on their surface. The quantity of these groups can vary widely depending on the type and ratios of monomers used in the polymerization process or the degree of secondary surface modifications that have been done. Some common particle functionalities are shown in Figure 14.6. Many of these functionalized particles can be used to couple covalently biomolecules through the appropriate reaction conditions (Ilium and Jones, 1985 Arshady, 1993). For each type of particle, manufacturers may offer several different densities of functional groups for different applications. 

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