Xylan sulfated

Xylan sulfates are mostly studied with regard to their biological activities. Usually, sulfuric acid, sulfur trioxide or chlorosulfonic acid are employed as sulfating agents alone or in combination with alcohols, amines or chlorinated hydrocarbons as reaction media (9). 

Biosorption is a rather complex process affected by several factors that include different binding mechanisms (Figure 10.4). Most of the functional groups responsible for metal binding are found in cell walls and include carboxyl, hydroxyl, sulfate, sulfhydryl, phosphate, amino, amide, imine, and imidazol moieties.4 90 The cell wall of plant biomass has proteins, lipids, carbohydrate polymers (cellulose, xylane, mannan, etc.), and inorganic ions of Ca(II), Mg(II), and so on. The carboxylic and phosphate groups in the cell wall are the main acidic functional groups that affect directly the adsorption capacity of the biomass.101... 

Most structural work on xylan has been done on that from esparto grass and the principal attack made by way of the methyl ether. Xylan can be methylated by heating with methyl iodide and silver oxide,92-93 but complete etherification is difficult and considerable degradation probably occurs. On the other hand, complete etherification is attained by methylation in two operations with potassium hydroxide and dimethyl sulfate to give a dimethylxylan in almost quantitative yield70 showing [< ]22d — 92° in chloroform. Methylation with potassium hydroxide appears to proceed more readily than with sodium hydroxide.70-92... 

Such enzymatic catalyzed polycondensations have allowed the synthesis of a number of natural polysaccharides, but has also allowed the production of nonnatural polysaccharides such as cellulose-xylan hybrids and functionalized hyaluronan, chondroitin sulfate, and chondroitin. Such work illustrates the ever-narrowing bridge between natural and synthetic polymers and polymer syntheses. 

Figure 2. Elution patterns of the ammonium sulfate-precivitated enzyme preparation from a DEAE-Sephadex A-50 column. (A) fi-glucosi-dase activity (3-hr incubation) of eluates diluted 60-fold, (A) xylan-saccharifying activity (3-hr incubation) of eluates diluted 60-fold, ( ) protein concentration measured in terms of the absorbance at 280 nm column 5.0 X 50 cm flow rate 20 mL/8 min one fraction 20 mL.

Figure 2.8 Summary of behavior of phenolic acid esters and free forms in the GIT and the liver. 5-O-CQA, 5-O-caffeoylquinic acid 5-O-FAAF, 5-O-feruloyl-L-arabinofura-nose C, conjugate (sulfate, glucuronide or methyl) CA, caffeic acid FA, ferulic acid FA-FA, dimer of ferulic acid FA-oligosac., ferulic acid esterified to an oligosaccharide FA-Xy, ferulic acid esterified to xylan R, alkyl group.

Among the plant polysaccharides there may be mentioned the hemi-celluloses the most common of these contain 4-O-methyl-D-glucuronic acid as branch units linked to a /3-D-xylan backbone.110 The commercially important gum arabic, a soluble polysaccharide produced by Acacia trees and widely used in foods and pharmaceuticals, also contains glucuronic units.111 D-Glucuronic acid has been found in sulfated complex polysaccharides from brown algae.112... 

FIGURE 1 Potential hydrolysis rates of six structurally distinct polysaccharides in seawater (A) and surface sediments (B) from Skagerrak and Svalbard. Pull = pullulan, lam = laminarin, xyl = xylan, fu = fucoidan, ara = arabinogalactan, chon = chondroitin sulfate. Note the differences in scale on the y axes for sediments and for seawater. [Skagerrak data from Arnosti (2000).]... 

Partially methylated and sulfated agaran—agarose hybrids (porphyrans) Sulfated xylomannans and neutral xylans Typical agars... 

Neutral xylans and sulfated galactans of die agar group Highly modified galactans of the agar group and DL-hybrids... 

A. I. Usov, K. S. Adamyants, S. V. Yarotsky, A. A. Anoshina, and N. K. Kochetkov, Polysaccharides of algae. 14. Isolation of sulfated mannan and neutral xylan from the red alga Nemalion vermiculare, Zh. Obshch. Khim., 44 (1974) 416 120 (in Russian). 

A. I. Usov and I. M. Dobkina, Polysaccharides of algae. 43. Neutral xylan and sulfated xylomannan from the red seaweed Liagora valida, Sov. J. Bioorg. Chem., 17 (1991) 596-603 (English translation from Bioorg. Khim., 17 (1991) 1051-1058). 

P. Mandal, C. A. Pujol, E. B. Damonte, T. Ghosh, and B. Ray, Xylans from Scinaia hater. Structural features, sulfation and anti-HSV activity, Int. J. Biol. Macromol., 46 (2010) 173-178. 

Schoettler has studied the alkali resistance of the xylan in pulps made from aspen wood. Verifying and extending previous work by March, he" observed a higher content of xylan resistant to 17.5% sodium hydroxide in aspen alkaline pulps (sulfate or soda process) than in aspen, chlorite holo-cellulose. Further chlorite treatment of an alkaline pulp did not reduce its xylan or resistant-xylan content. Alkaline (sulfate) cooking of the holo-cellulose did not increase the resistant-xylan content. These results are summarized in Table X. 

Bleached, soda pulp contained about the same amount of resistant xylan as bleached, sulfate pulp, and a bleached, sulfite pulp contained only a small amount (Table X). In this same study," it was observed that the resistant-xylan content was greater in an air-dried or oven-dried pulp than in the same pulp before drying (see Table XI). In agreement with the work of Meller," a reduction in resistant xylan resulted from mechanical beating or grinding. 

The recent studies of the Finnish group further emphasize the complexity of the xylan in wood cellulose. These workers have shown that the properties of the xylan in wood pulps depend not only on the method of pulping but also on the type of raw material. It was observed that, when pulps are prepared by the (acidic) sulfite process from the softwoods, pine and spruce, a substantial part of the xylan is of the acidic type (see Fig. 2, p. 303). Even when these sulfite pulps are refined further with hot alkali, some acidic xylan remains. However, when pulps are prepared from pine and spruce by the (alkaline) sulfate process, the acidic xylan is removed and only neutral xylan remains. 

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