L-guluronic acid units

Chitosan, a copolymer of 2-amino-2-deoxy-D-glucopyranose and 2-acetamido-2-deoxy-D-glucopyranose units, and alginate, a linear copolymer of b-(l,4)-linked D-mannuronic acid and a-(l,4)-linked L-guluronic acid units, have been spun into useful fibers. However, because of low mechanical properties they are mostly limited to medical and other non-load-bearing specialty applications [58]. Further information about chitosan fiber can be obtained elsewhere in this book. 

Because the 3,6-anhydrogalactopyranose unit has the L-configuration, it exists in the 1C conformation. This is similar to the 3,6-anhydro-o-galactopyranose units of the k- and i-carrageenans and of the L-guluronic acid units of alginic acid. 

It is a linear glycuronoglycan that consists mainly of p-l,4-linked D-mannuronic and L-guluronic acid units in the pyranose ring form, the relative proportions of which vary with the botanical source and state of maturation of the plant. 

Pneumococcus, polysaccharides from, 6-7 Poly(a-L-guluronic acid), 353, 355-356,415 Poly(P-D-mannuronic acid), 353-354,414 Polysaccharides, 311 -439 amino sugar derivatives, 166 chemical repeating units, 321, 324-325... 

Figure 8.5 D-Mannuronic and L-guluronic repeat units of alginic acid...

Alginates are composed of (1—>4)-linked (3-D-mannuronic acid (M units) and a-L-guluronic acid (G units) monomers (Figure 16.9), with different sequential distribution along the polymer chain [142]. The composition, sequence, and molecular weight generally determine the physical properties of alginate [143]. 

The conformation of acidic polysaccharides and their interactions with calcium ions was examined by molecular simulation, and the authors demonstrated the existence of specific calcium binding with poly-a-L-guluronate [56, 57], The mechanism of complex formation involves calcium interactions with different oxygen atoms of two adjacent guluronic acid units and with two inter-chain units, as visualized in the egg-box model (Fig. 24.7). The mechanism of gelation is a two-step process first step is a dimer formation, followed by precipitation for small chains, or gelation for long ones formed with different types of blocks. 

Alginic acid is a linear multiblock copolymer from blocks of jS-(l->4)-D-mannuronic acid and a-(1 4)-L-guluronic acid, as well as alternating copolymers from these two monomer units. In natural products, the molecular weights reach about 150,000 and with regenerated products 30,000-60,000. Alginates are the salts of alginic acid. 

Biodispersion Alteromonas sp. Alteromonas haloplanktis Alteromonas madeodii Heteropolysaccharide containing repeating tetrasaccharide units [L-Rha —> 2-acetamido —> 2-deoxy-D-Glu —> 3-0-[(R)-l-carboxyethyl]-D-Glu] [o-Gal —> 3-0-acetyl-2-acetamido-2-deoxy-DGIu —> 2-acetamido-2-deoxy-L-guluronic acid —> 3,6-dideoxy-3-(4-hydroxybutyramido)-D-Gal]... 

Algin is a copolymer containing blocks of the two types of residues [99] and segments that alternate in a fairly regular manner [100] (see Fig. 6.12A). X-ray diffraction studies have indicated that the D-mannuronic acid units are in the Cl C Cj) conformation, and the L-guluronic acid residues are in the 1C ( C ) conformation [101]. The combination of these conformational features is unusual and gives unique properties to the alginates. 

---