Complex carbohydrates acid hydrolysis

Fraction Fla was chosen for structural purposes due to its better solubility in water and the absence of Xyl. In order to remove noncovalently associated protein, fraction Flap was submitted to sequential shaking cycles with a mixture of chloroform-buthanol, as indicated by Sevag and described by Staub [17]. The fraction was also treated with trichloroacetic acid. In both procedures, coprecipitation of carbohydrate and protein was observed, suggesting strong linkages and a more complex structure. Fla as was submitted to mild acid hydrolysis yielding Flas and Flap (Table VI). 

A feasible way of introducing acid-stable linkages into carbohydrates is N-deacetylation. This can be achieved with hydrazine.59,70,71 The use of sodium hydroxide-sodium benzenethioxide in aqueous dimethyl sulfoxide for this purpose has also been described72 The difference in the acid hydrolysis of N-acetylhexosamine-con-taining carbohydrates before and after N-deacetylation was used in the study of complex glycoprotein saccharides from human erythrocyte membranes.73-75 Methylation analysis of the glycopeptides prepared... 

The reaction mechanism of a-amylases is referred to as retaining, which means that the stereochemistry at the cleaved bond of the carbohydrate is retained. Hydrolysis of the glycosidic bond is mediated by an acid hydrolysis mechanism, which is in turn mediated by Aspl97 and Glu233 in pig pancreatic amylase. These interactions have been identified from X-ray crystallography. The aspartate residue has been shown to form a covalent bond with the Cl position of the substrate in X-ray structure of a complex formed by a structurally related glucosyltransferase. " The glutamate residue is located in vicinity to the chloride ion and acts as the acidic catalyst in the reaction. The catalytic site of a-amylases is located in a V-shaped depression on the surface of the enzyme. 

PENTOSAN. A complex carbohydrate (hemicellulose) present with the cellulose in many woody plant tissues, particularly cereal straws and brans, characterized by hydrolysis to give five-carbon-atom sugars (pentoses). Thus the pentosan xylan yields the sugar xylose (HOH,C CHOH CHOH CHOH CHO) that is dehydrated with sulfuric acid to yield furfural (C5H4O2). 

Carbohydrates are classified as either simple or complex. Simple sugars, or monosaccharides, are carbohydrates such as glucose and fructose that can t be broken down into smaller molecules by hydrolysis with aqueous acid. Complex carbohydrates, or polysaccharides, are compounds such as cellulose and starch that are made of many simple sugars linked together. On hydrolysis, polysaccharides are cleaved to yield many molecules of simple sugars. 

The indium-mediated Barbier reaction has certainly become one of the most popular reactions for creating a carbon-carbon bond under aqueous conditions and has led to spectacular developments in recent years. Compared to other metals, indium is resistant to oxidation, hydrolysis, and has a very low first ionization potential (5.79 eV, in contrast to the second one which is quite normal) which confers on it a remarkable reactivity in Barbier-type reactions. In 1991, Li and co-workers reported the first allylation of aldehydes and ketones mediated by indium in water without any additives or special activation [133]. In particular, the use of indium allowed reactions with acid-sensitive compounds [134] or the preparation of complex carbohydrates such as deaminated... 

Sugars in ARP liquid exist only in oligomer form, i.e., xylo-oligosaccharides (XOS). After acid hydrolysis of the ARP liquor, large amount of xylose monomer appears. It proves that hemicellulose sugars in the ARP liquor is either in the form of XOS or lignin carbohydrate complex. Hemicellulose removal in ARP is proportional to the extent of lignin removal. The reason for this is unclear at this time. 

The cinerubins, although related to pyrromycin and the rhodomycins in their aglycon portion, are more complex antibiotics and yield three carbohydrate moieties on acid hydrolysis. " One of these is nitrogenous and is reported to be identical with, or closely related to, rhodosamine or de-sosamine. No further characterization of these sugars has yet been published. 

Wood contains from 8 to 10 per cent of a gum which is a mixture of complex carbohydrates. Wood gum yields xylose on hydrolysis and, like other substances which contain pentosans, is. converted into furfural on boiling with hydrochloric acid. The formation of furfural, it will be recalled, is a test for a pentose (365). 

The cellular tissue of many fruits contains cellulose associated with other substances of the nature of carbohydrates. Apples, pears, and other fruits contain a substance called pecto-cellulose, which is probably a chemical compound of cellulose and pectin, as it gives cellulose and pectic acid on hydrolysis with an alkali. Pectin, which is a complex carbohydrate present in certain fruits, is converted into pectic acid when heated with a solution of an alkali. The formation of jellies from fruits is brought about as the result of the hydrolysis of the pectin which they contain. The hydrolysis converts pectin into pectic acid, which forms calcium pectate with the calcium salts always... 

First, humus-like substances may be formed by the action of mineral acids upon hexose sugars, as has long been known. More complex carbohydrates are first broken down into their monose derivatives. After hydrolysis the transition products may undergo rapid condensation with a piling up of molecular weight to form insoluble humins . Attempts to identify these compounds or fractions of these mixtures were not successful. 

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