Polysaccharides periodic acid oxidation

There are two general methods for the determination of the character of the linkage of polysaccharides periodic acid oxidation (1,2) and methylation analysis (3). The present paper gives details of the possibilities for the utilization of the periodate oxidation. 

Information about irregularities in the polymer chain was gained by studying the total periodate oxidation of the polysaccharide. Periodic acid or its salts react with a-diols to give rise to two carbonyl groups and iodate. In case of three adjacent hydroxyl groups the initially formed a-hydroxy aldehyde undergoes further oxidation with formation of one equivalent of formic acid ... 

Carbohydrates. Mild oxidants such as chlorine, bromine, or iodine readily convert the aldehyde end groups in the wood polysaccharides to aldonic acid end groups. Nitrogen dioxide selectively converts the primary hydroxyl groups on C-6 in cellulose to carboxyl groups (J3). Periodic acid is a specific oxidant for vicinal diols and yields formaldehyde from primary hydroxyl groups and aldehydes from secondary. 

Vicinal diol functions are oxidized with a high degree of specificity using periodic acid. Dialdehyde polysaccharides are formed [111,112]. 

In polysaccharides oxidized with periodic acid, one molar proportion of each individual, oxidized monosaccharide reacts with only one mole of... 

In combination with other methods, use of the formazan reaction facilitates the study of polysaccharides of unknown structure and determination of the linkages in them. For example, if, from water-soluble polysaccharides, water-insoluble, highly nitrogenous formazans are prepared after oxidation with periodic acid, the estimation of the results of the periodate oxidation is greatly facilitated, since the precipitate is free from interfering, non-trans-formed byproducts. Similar favorable features were observed by Barry and Hirst - on isolating phenylhydrazones and other nitrogenous con-... 

The selective periodate oxidation can be actually used to fragment a polysaccharide as well as to provide aldehydic groups. A mild periodate oxidation of a-2,9-linked polysialic acids can result in fragmentation yielding dialdehydic fragments. Similarly, 1,5-phosphorylated ribitol in the Haemophilus influenzae polysaccharide can be oxidized with periodate to provide dialdehydic products. These dialdehydic products actually can be used to cross-link between modified proteins. 

DifiBculty is sometimes experienced in hydrolyzing periodate-oxidized polysaccharides with acid, because they contain stable, anhydro rings. If, however, the periodate-oxidized polysaccharide is first reduced to its corresponding polyalcohol, fragments characteristic of structural units in the parent polysaccharide may readily be obtained from the polyalcohol on hydrolysis with dilute acid. When this improved degradative... 

The halogens and their oxyacids probably are the most important oxidants used in the carbohydrate field. They are widely used as bleaching agents, but the mechanism of this action remains to be clarified. As reagents for preparatory purposes (particularly for aldonic acids and lactones) and for analytical procedures, they are very important. Periodic acid, discussed in a later section, has an important application for the elucidation of structures of carbohydrates. A number of valuable commercial products are made by treatment of polysaccharides with halogens, particularly chlorine or hypochlorous acid, but the nature of these actions, such as the modification of starch, has not been clarified. 

As shown in Figure 5.20, the oxidation of starch results in the addition of two aldehyde groups to individual glucose molecules within the polymer chain. The advantage of using periodic acid lies in the specificity of its oxidation. It facilitates the formation of aldehydes within the polysaccharide molecule. The extent of oxidation of the polysaccharide polymer can be controlled by, for example, the amount of oxidizer added, the duration of the oxidation process, and/or the temperature of the reaction. For example, the oxidation time needed for the oxidation of starch can be attained in about 24h. Specifically, at least about 15% of the hydroxyl groups are oxidized, and more specifically, about 35 to about 100% of the hydroxyl groups are oxidized [99]. 

Oxidation of polysaccharides using 10 mM or greater concentrations of sodium periodate at room temperature results in the cleavage of adjacent hydroxyl-containing carbon-carbon bonds on other sugars besides just sialic acid residues (Lotan et al., 1975). High concentrations... 

Figure 23.9 Reaction of adipic acid dihydrazide with (strept)avidin produces a hydrazide derivative that is highly reactive toward periodate-oxidized polysaccharides.

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