Polysaccharides oxidants and

From the formazan formation, it is possible to conclude the structure of the oxidized polysaccharides and their phenylhydrazones. 

X. Preparation and Use of the Tetrazolium and Carbothionic Acid Phenylhydrazide Derivatives of the Oxidized Polysaccharides and the Metal Complexes of Their Formazans... 

Formazans of Periodate-oxidized Polysaccharides and Their Derivatives... 

Much attention has been given to finding efficient procedures for the dismantling of oxidized polysaccharides, and also to methods for the separation and characterization of product mixtures. Of the fragmentation procedures employed (see Section VI. 1), that " in which the dialdehyde is reduced, and the polyol formed is subjected to total acid hydrolysis, is the most widely applied. (Although the procedure is sometimes referred to as the Smith degradation , this term is more commonly reserved for selective hydrolysis of the polyol under milder acidic conditions (see Section VI.4.) In one variation,the dialdehyde is methylated prior to reduction with borohydride, which differentiates free hydroxyl groups in the oxidized polymer from those formed upon reduction of the aldehydes. 

Universal calibration plot for polyethylene glycol, polyethylene oxide, polysaccharide, and polyacrylamide in 0.10 M sodium nitrate at 35 C. 

The anomeric configurations of the sugar residues were determined by chromium trioxide oxidation [14], Oxidation of the fully acetylated polysaccharide and subsequent monosaccharide analysis by GLC indicated that the D-Xyl units are P-linked (oxidized more rapidly) and that die D-GlcA are a-linked (Table II). 

A practical method of modification of polysaccharides by clean oxidation using H2O2 as oxidant and cheap iron phthalocyanine as catalyst has been developed. Since no acids, bases or buffers and no chlorinated compounds were used, a pure product can be recovered without additional treatment. Importantly, this flexible method provides materials with a wide range of DScho and DScooh just by an appropriate choice of the reaction conditions. Oxidized polysaccharides thus obtained possess various, tailormade hydrophihc/hydrophobic properties which have been tested successfully in cosmetic and other apphcations. 

A breaker an enzyme (at T<140°F), strong oxidizing agent, or an acid, is used to depolymerize polysaccharides and break crosslinks such that viscosity declines at a controlled rate so that the proppant may be deposited in the fracture. Too rapid proppant dropout would cause a premature "sand-out" which prevents future extension of the fracture. Peroxydisulfates are the most frequently used breakers. Less reactive organic peroxides may be preferred for high temperature formations (85). 

Injectivity can be reduced by bacterial slime which can grow on polysaccharides and other polymer deposits left in the wellbore and adjacent rock. Strong oxidizing agents such as hydrogen... 

Low-volatility natural organic material such as polysaccharides and higher molecular weight proteins sometimes produced low results. In the Hannaker and Buchanan method [82] these problems are overcome by using a solution-phase oxidant and enclosing the system in a sealed tube. In this way all of the constituents are fully contained and exposed to oxidation and, moreover, oxidation of the organic matter to carbon dioxide is complete for the greater majority of compounds. 

D-xylopyranose units. This structural concept is substantiated by estimation of the formic acid obtained when the xylan is oxidized by periodate ions. On hydrolysis of the fully oxidized xylan there is obtained a small amount of D-xylose which presumably occupied the branch points in the polysaccharide and consequently was protected from periodate oxidation by possessing no adjacent free hydroxyl groups. 

Metal ions of transition and other elements of variable valency, e.g. Ce, Co, Fe, V, Mn, etc., are known to oxidize polysaccharides rather selectively, producing macroradicals as intermediates which are capable of adding vinyl monomers and form graft copolymers. These initiators are redox systems which differ from those previously described by not producing free radicals of low molecular weight. Only macroradicals on the substrate are formed in the redox reaction. Some homopolymer may still be formed in the process, e.g. due to oxidation of monomer or other side reactions. ... 

Abiontic, involving free extracellular enzymes or solubilizing agents, enzymes bound to soil surfaces, enzymes within dead or non-proliferating cells, or enzymes associated with dead cell fragments. Extracellular enzymes are important in the initial stages of organic matter oxidation, in which polysaccharides and proteins are hydrolysed to soluble compounds that can be absorbed by microbial cells and further oxidized in biotic processes. 

Following comparison to sound wood (Figs. 5A and 5B), it was clearly evident that degraded wood had undergone oxidation. This oxidative process could take place on both polysaccharides and lignin (22,23), and could therefore represent a general degradation mechanism of the wood cell wall polymers. 

Here we report an overview of the different heterogeneously-catalyzed pathways designed for the selective conversion of carbohydrates. On the basis of these results, we shall try to determine the key parameters allowing a better control of the reaction selectivity. Water being commonly used as solvent in carbohydrate chemistry, we will also discuss the stability of solid catalysts in the aqueous phase. In this review, heterogeneously-catalyzed hydrolysis, dehydration, oxidation, esterification, and etherification of monosaccharides and polysaccharides are reported. 

Fig. 7 Maltotetraose hybrids with various carriers resulting in different chain architectures A poly(ethylene oxide) Ba and Bb poly(acrylic acid), amylose, cellulose, and other polysaccharides Ca cyclodextrin and multifunctional acids Cb amylopectin D crosslinked poly(acryl amide) [156] - Reproduced by permission of Wiley...

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