D-mannuronic acid units

The molecular weight of the sodium salt of alginic acid has been determined by measurements of osmotic pressure in sodium chloride solution.88 The n/C versus C curve was found to be independent of salt concentration for values between 0.2 N and 0.5 JV, and the slope of the curve was the same for a series of seven fractions with values of molecular weight between 48,000 and 186,000 (220-860 D-mannuronic acid units). Intrinsic viscosity measurements showed the coefficient a in the modified Staudinger s equation88 to be 1.0 and the approximate value of Km to be 15(10)-4. 

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. 

Some investigators claim that alginic acid is unique in that D-mannuronic acid units seem to make up its entire structure whereas others believe that the less than theoretical yields of carbon dioxide obtained by the hot acid decarboxylation of alginic acid indicates the presence of a small proportion... 

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... 

D-mannuronic acid residues joined by /3-1,4-gIycosidic linkages,84 and to have a chain length of about 100 hexuronic acid units.86... 

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]. 

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. 

Polyuronides macromolecular compounds found in plants, consisting of units of uronic acids in the pyr-anose form (see Carbohydrates). The main components are o-glucuronic acid, o-galacturonic acid and D-mannuronic acid. P. contain free carboxyl groups and are consequently more strongly hydrated than polysaccharides formed from neutral monosaccharides. Examples are pectins, alginic acid and plant mucilages. 

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. 

Another polyuronide is alginic acid, present in marine algae and formed of chains of about one hundred units of D-mannuronic acid, joined together by l 4-j8-glucoside linkages. 

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