Alginic acid structure

Figure 22.11. Cellulose is a structural and rather chemically inert component of terrestrial plants. Alginic acid is synthesized by marine algae and has medicinal properties. Some polysaccharides contain nitrogen in the form of amino sugars. The primary example of this is chitin, which composes the exoskeletons of Crustacea. An amino sugar contains an amine in place of a hydroxyl group. In other polysaccharides, sugars combine with lipids and proteins. These form glycoUpids and glycoproteins, respectively.

Algin occurs in all members of the class Phaeophyceae> brown seaweed, as a structural component of the cell walls in the form of the insoluble mixed calcium, magnesium, sodium, and potassium salt of alginic acid. 

Formation of L-guluronic acid, a component of the alginic acid-like polysaccharide produced by P. aeruginosa and Azotobacter vinelandii, requires special comment. In this case, a polymer built from /3-(l- 4)-linked D-mannosyluronic acid residues serves as an intermediate in the biosynthesis.204,205 Part of the D-mannosyluronic acid residues in the polymer is subjected to an epimerization at C-5 catalyzed by an exocellular enzyme of the micro-organism,205-207 producing a polysaccharide composed of structural blocks that contain only D-mannosyluronic acid or only l-gulosyluronic acid residues, as well %s some having both. The mechanism of the epimerization remains unclear. 

The adsorption of albumin from aqueous solution onto copper and nickel films and the adsorption of B-lactoglobulin, gum arabic, and alginic acid onto germanium were studied. Thin metallic films (3-4 nm) were deposited onto germanium internal reflection elements by physical vapor deposition. Transmission electron microscopy studies indicated that the deposits were full density. Substrate temperature strongly Influenced the surface structure of the metal deposits. Protein and/or polysaccharide were adsorbed onto the solid substrates from flowing... 

Proof of the structure of the uronic acid was obtained by Hirst, Jones and Jones,46 who isolated the methyl glycoside methyl ester by methyla-tion of the products from the graded methanolysis of alginic acid. The tri-O-methyl-D-mannuronic acid was converted to the diamide of 2,3,4-tri-O-methyl-D-mannaric acid, which had previously been prepared from... 

Investigations by X-ray methods have indicated that alginic acid possesses a fiber structure analogous to that of cellulose.86 An estimate of the molecular weight was obtained by Heen87 from a study of the viscosity of solutions of the acid in 2 JV sodium hydroxide. The values found, (14,100-15,400), corresponded to a degree of polymerization of about 80, but these were considered to be approximations only, as it was uncertain whether or not Staudinger s formula could be applied. 

From the evidence yet available it is not possible to determine definitely whether alginic acid possesses a linear or a slightly branched structure. 

Figure 14.33. Structures of guluronic acid and mannuronic acid and the 100-MHz l3C spectrum of alginic acid. (From ref. 8. Reprinted with permission of Elsevier Science S.A.)...

A. I. Usov, Alginic acids and alginates Analytical methods used for their estimation and characterization of composition and primary structure, Russ. Chem. Rev., 68 (1999) 957-966 (translated from, Uspekhi Khimii, 68 (1999) 1051-1061). 

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