Hydrazide Functional Groups

Hydrazide-containing reagents can be used for probing or conjugation of carbonyl-containing compounds, including macromolecules possessing aldehydes and ketones. 

The creation of hydrazide probes most often is based on the derivatization of a detectable molecule with a fcr s-hydrazide compound. Although hydrazine itself (in the form of hydrazine hydrate) can be used in a methanolic solution to modify activated carboxylate molecules forming hydrazides, the availability of the bifunctional hy-drazides provides a built-in spacer to accommodate greater steric accessibility. 

The following protocols make use of the compounds adipic acid dihydrazide and carbohydrazide to derivatize molecules containing aldehydes, carboxylates, and al-kylphosphates. The protocols are applicable for the modification of proteins, including enzymes, soluble polymers such as dextrans and poly-amino acids, and insoluble polymers used as microcarriers or chromatographic supports. 

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On the other end of the cross-linker, the hydrazide functional group can react with periodate-oxidized carbohydrate molecules to form hydrazone linkages (Chapter 1, Sections 2 and 4.5). Thus, glycoproteins can be targeted specifically at their polysaccharide chains, avoiding cross-linking at active sites which can lead to activity losses (Fig. 167). 

BODIPY 530/550 C3 hydrazide is 4,4-difluoro-5,7-diphenyl-4-bora-3a,4a-diaza-s-indacene-3-propionyl hydrazide, a derivative of the basic BODIPY structure, which contains two phenyl rings off the No. 5 and 7 carbon atoms and a propionic acid hydrazide group on the No. 3 carbon atom (Molecular Probes). The hydrazide functional group reacts with aldehyde- or ketone-containing molecules to form hydrazone linkages (Fig. 229). The compound may be used to label glycoproteins or other carbohydrate-containing molecules after oxidation of their polysaccharide portions with sodium periodate to yield aldehyde residues. 

Hydrazide functional groups can react with carbonyl groups to form stable hydrazone linkages. Derivatives of proteins formed from the reaction of their carboxylate side chains with adipic acid dihydrazide (Chapter 4, Section 8.1) and the water soluble carbodiimide EDC (Chapter 3, Section 1.1) create activated proteins that can covalently bind to formyl residues. Hydrazide-modified enzymes prepared in this manner can specifically bind to aldehyde groups formed by mild periodate oxidation of carbohydrates (Chapter 1, Section 4.4). These reagents can be used in assay systems to detect or measure glycoproteins in cells, tissue sections, or blots (Gershoni et al., 1985). 

Schiff base cross-linking involves the reaction between macromolecules containing alcoholic, aminic, or hydrazide functional group with aldehydes to obtain a hydrogel... 

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