Polyuronides uronic acids

Polyuronide Uronic acid, fucose, galactose, mannose [44]... 

Norris and Resch determined furfural yields from uronic acids, under the conditions normally used for pentosan determination, and obtained about 37 to 44% of the theoretical yield of furfural. In later work, the effect of various furfural-yielding substances on one another was ascertained, and a standardized procedure was developed for analysis of the types of mixtures commonly met with in cell-wall chemistry. Apparently, the yield of furfural from uronic acids and polyuronides varies with the proportion of these substances present, and with their ratio to other sugars. From oxycellulose, TJnruh and Kenyon obtained furfural yields of 18 to 20 % of the theoretical on the basis of carboxyl content. Wise and Ratliff, however, in summative analysis of wood, used a correction based on the assumption that the uronic acids present evolve 35% of the theoretical amount of furfural. 

The carbohydrate analyses reported by Sundman, Saarnio and Gustafs-son for sulfate pulps are listed in Table XVII. These results were obtained by quantitative, paper chromatography on completely hydrolyzed samples. In another study,"" the uronic acid anhydride content of some wood pulps was determined. It was noted " that sulfate pulps prepared from hardwoods retain a considerable proportion of uronic acid, whereas sulfate pulps from softv oods may be entirely free from polyuronides. 

Polyuronides may be defined as polysaccharides that contain one or more uronic acid units in their molecular structures. They have a frequent and wide occurrence in nature. Much of the carbohydrate material in plants belongs to the group. It includes all pectic materials and plant gums and many plant mucilages, hemicelluloses and gel-forming substances and some microbial polysaccharides. These substances are to be looked for in water-soluble plant exudates and mucilages, as well as in water and alkaline extracts of most plant materials. This review will be limited to the polyuronides occurring in plants. 

If the plant compound gives the naphthoresorcinol test for a uronic acid and on hydrolysis with a hot dilute solution of a strong acid gives simple sugars and aldobionic or free uronic acids, it is a polyuronide. " ... 

The analytical determinations most often made on a polyuronide before it is hydrolyzed are those for uronic acid, pentosan, methyl-pentosan, methoxyl and ash. The percentage of hexosan is usually estimated by difference. When the polyuronide has been obtained as a free acid it can in many cases be titrated with a base. Such metals as sodium, potassium, magnesium, calcium and iron often occur and especially so in plant gums and mucilages. 

Pentosan and methylpentosan determinations are described in standard works. When these determinations are made on polyuronides, they are inaccurate and of restricted use in calculating the relative number of pentosan and methyl pentosan units per uronic acid unit. This is especially true when pentoses, methylpentoses and hexoses occur together in a polyuronide. 

Three types of carbon-oxygen linkages may occur in a polyuronide ester, ether and glycoside. The ester-linked methyl group of pectins is split by cold dilute alkali. It may also be removed by certain enzymes. Methyl groups which often occur ether-linked to the uronic acid especially in plant gums and hemicelluloses, resist hydrolysis by mineral acid solutions of 2 to 4% concentrations, even in the autoclave. Such groups survive hydrolytic conditions that are usually chosen. 

Three uronic acids occur in nature, D-galacturonic, D-glucuronic and D-mannuronic acids. No polyuronide is known that contains two different uronic acids. D-Glucuronic acid containing an ether-linked methyl group occurs in mesquite gum. It probably is the monomethyluronic acid that occurs in many hemicelluloses. - ... 

The identification of the uronic acid in a polyuronide is somewhat difficult because during hydrolysis a large part of it is destroyed, and the free acid finally obtained is contaminated with decomposition and reversion products as well as with low polymers resulting from incomplete... 

J. E. Scott and R. J. Harbinson, Periodate oxidation of acid polysaccharides. II. Rates of oxidation of uronic acids in polyuronides and acid mucopolysaccharides, Histochemie, 19... 

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