Modification and conjugation

The most significant amino acids for modification and conjugation purposes are the ones containing ionizable side chains aspartic acid, glutamic acid, lysine, arginine, cysteine, histidine, and tyrosine (Figure 1.6). In their unprotonated state, each of these side chains can be potent nucleophiles to engage in addition reactions (see the discussion on nucleophilicity below). 

Cysteine sulfhydryls and cystine disulfides may undergo a variety of reactions, including alkylation to form stable thioether derivatives, acylation to form relatively unstable thioesters, and a number of oxidation and reduction processes (Figure 1.10). Derivatization of the side chain sulfhydryl of cysteine is one of the most important reactions of modification and conjugation techniques for proteins. 

This section describes the basic chemical attributes of carbohydrate molecules. Principal sites of reactivity on carbohydrates are discussed with the aim of developing a rational approach to using them in modification and conjugation procedures. 

In this section, the chemistry and structure of nucleic acids and oligonucleotides is discussed with a view to creating functional conjugates with detectable molecules. The corresponding strategies and protocols associated with DNA or RNA modification and conjugation can be found in Chapter 27. 

To maximize the modification of amines and minimize the effects of hydrolysis, maintain a high concentration of protein or other target molecule. By adjusting the molar ratio of crosslinker to target molecule(s), the level of modification and conjugation may be controlled to create an optimal product. 

Although there are a number of photo-sensitive coupling chemistries that have been used in modification and conjugation reactions (Chapter 2, Section 7), it has been primarily aryl azides... 

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