Alginate chemical structure

Figure 7.2 Schematic representation of alginate cross-linking with divalent cations and the chemical structure of the constituent repeat units, guluronate (G) and mannuronate (M). Carboxylate groups present along the backbone (largely from the G residues) interact with multivalent cations to yield metal ion cross-linked gels.

Alginates are linear co-polymers of randomly arranged P-D 1,4 mannuronic acid (M) and a-L 1,4 guluronic acid (G) blocks as represented in Fig. 5.3. Its chemical structure is similar to that of cellulose except that it has a carboxyUc group on the C5 position instead of a methylol group in the case of cellulose. 

The same procedure of catalyst synthesis applied to other polysaccharides, such as -carrageenan and chitosan, allowed data on the influence of the chemical structure of the support to be obtained. The differences in turnover numbers (moles of product per moles of Pd per hour), close to 500 for alginates, 190 for carrageenan, and only 40 for chitosan, indicated that the activities were correlated to the electrostatic properties of the support. Carrageenans only bear one sulfate group per two saccharide monomers, while alginate presents one carboxylic group... 

Alginate is also a naturally occurring linear polysaccharide extracted from seaweed, algae, and bacteria. The fundamental chemical structure of alginate is composed of (l )-b-o-mannuronic acid... 

FIGURE 31.5 Chemical structure of alginate showing the a-L-guluronic and P-D-mannuronic acids blocks. 

FIGURE 53.1 Chemical structure of alginates, where m and n stand for whole numhers signifying the number of monomers present in the polymeric form. 

Chemical structure Intermolecular interaction between hydroxyl group of BC and carboxyl group of alginate [23, 31,40,42]... 

It is known that sulfated polysaccharides, including natural and synthesized ones, had great blood-compatibility or even anticoagulant activity [34]. After sulfation of sodium alginate, its derivative contains both sulfate and carboxyl groups, whose chemical structure is analogous to the natural blood anticoagulant heparin. Fan et al. 

Fig. 2 Supramolecular natural polymeric hydrogels discussed in this chapter, (a) Chemical structure of the most-repeated sequence in collagen, forming the a-chain that folds in a three-stranded superhelix [135]. These superhelices bundle to fram the collagen fiber, (b) Representative chemical structure of fibroin and the antiparallel p-sheet formation connected by hydrophilic linkers, (c) Chemical structure of alginic acid, cross-linked by calcium ions (highlighted), (d) Left Top view of two a-helixes of keratin forming a coiled coll by hydrophobic interactions. Right Overview of subsequent formation of the fibril. The left part is adapted from [57] with permission of The Royal Society of Chemistry...

FIGURE 5.6 Chemical structure of alginic acid, genipin, and four diamines used for modification. 

The molecular structure of alginates may be considered from three different though interrelated points of view. There is the chemical structure which describes the nature and sequence of constituent units, the conformations which describe the arrangement in space and the intermolecular interactions. These are discussed in this section. 

Figure 6.3 Chemical structures of G-block, M-block, and alternating block in alginate. Reprinted with permission from Lee and Mooney (2012). Copyright 2012, Elsevier.

Figure 7.3 shows the chemical structures of p-o-mannuronic acid (M) and a-L-guluronic acid (G), which form the linear polymeric chains. These two monomers are stereochemically very different, as a result of their difference at C-5. As shown in Table 7.1, alginates extracted from different species of seaweed differ in M and... 

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