Monosaccharides, acid degradation

Acetals, nomenclature, 123-124 cyclic, nomenclature, 121-122 Acid degradation, monosaccharides, 457-459 Acid hydrolysis... 

Mills depiction, cyclic monosaccharides, 63 Monosaccharides, see also Aldoses acid degradation, 457-459 alkaline degradation, 449-455 mechanisms, 451... 

Despite the general complexity of DOM, which has been illustrated and discussed at length in this review, several percent of DOM can be attributed directly to lignins, lipids, proteins, and sugars, which are found in freshwaters both as their chemically bound forms and as their free forms. Mostly, these constituents of DOM exist as chemically bound forms, from which their respective monomers (lignin-derived phenols, simple carboxylic acids, amino acids, and monosaccharides) can be liberated by vigorous hydrolytic and/or oxidative degradation. 

Organic matter deposited in sedimentary or wetland habitats is composed of a complex mixture of biopolymers. Some of these compounds, such as proteins, carbohydrates, and lipids are easily degraded by microorganisms (i.e., labile), while other compounds, such as lignin and hemiceUulose, are resistant to decomposition (i.e., recalcitrant). Biopolymers are degraded in a multistep process. First, microorganisms simplify polymers to monomers such as amino acids, fatty acids, and monosaccharides (Figure 4). The monomers are further mineralized to CO2, or to a combination of CO2 and CH4. 

Degradation of A -linked glycoproteins completely to amino acids and monosaccharides is necessary to avoid the storage diseases mentioned above that have severe consequences for cells and tissues. This catabolism has been determined to occur in two major parts [9, 10] ... 

There are various methods of degrading monosaccharides to the next lower member of the series. Wohl (1893) devised a method which is virtually the reverse of the cyanhydrin ascent since it consists in the removal of hydrocyanic acid from the acetylated nitrile (CXLI) formed on acetylation... 

There are a number of well-known colour tests for monosaccharides, such as condensation of the acid degradation products with phenolic substances. Perhaps the most frequently cited example of this is the Molisch test in which carbohydrates give a purple colour with a-naphthol in the presence of concentrated sulphuric acid. The presence of ketoses and of 3,6-anhydro-hexoses is often detected by the characteristic red colour rapidly developed with acid resorcinol (Seliwanoff test), and the presence of 2-deoxypentoses may be shown by the deep blue colour they yield with diphenylamine after degradation with acid to 5-hydroxy-levulinaldehyde. Before an individual sugar can be identified, however, it must be isolated as a pure substance in crystalline form or converted to a characteristic crystalline derivative. The derivative the author considers the best for the characterisation of the better known monosaccharides is given in Table I (p. 57). 

Much of the chemistry of monosaccharides is the familiar chemistry of alcohols and aldehydes/ketones. Thus, the hydroxyl groups of carbohydrates form esters and ethers. The carbonyl group of a monosaccharide can be reduced with NaBH4 to form an alditol, oxidized with aqueous Br2 to form an aldonic acid, oxidized with HNO3 to form an aldaric acid, oxidized enzymatically to form a uronic acid, or treated with an alcohol in the presence of acid to form a glycoside. Monosaccharides can also be chain-lengthened by the multistep Kiliani-Fischer synthesis and can be chain-shortened by the Wohl degradation. 

Stage 2 Fatty acids, monosaccharides, and amino acids are degraded in cells to yield acetyl CoA. 

Monosaccharide residues containing vicinal hydroxyl groups are oxidized by periodate, and are subsequently removed in the reduction-hydrolysis step. Therefore, the positions to which such monosaccharide residues are linked can be located by methylation analysis performed before, and after, Smith degradation. Alternatively,59 the oxidized and reduced sample is methylated, the ether hydrolyzed, and the product realkylated with CD3I or CH3CH2I. This kind of procedure can have advantages over that first described. For example, methylation before the hydrolysis step hinders the acetal protection of hydroxyl groups that can occur in acid hydrolysis.7... 

In addition to the common pathways, glycolysis and the TCA cycle, the liver is involved with the pentose phosphate pathway regulation of blood glucose concentration via glycogen turnover and gluconeogenesis interconversion of monosaccharides lipid syntheses lipoprotein formation ketogenesis bile acid and bile salt formation phase I and phase II reactions for detoxification of waste compounds haem synthesis and degradation synthesis of non-essential amino acids and urea synthesis. 

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