Polysaccharides dialdehyde derivatives, preparation

There are multiple mechanisms of depolymerization, since many of the dialdehyde derivatives are highly susceptible to alkah-catalyzed -elimination, even at moderate temperatures and pH values. Moreover, the degradation of polysaccharide chains caused by free radicals may occur [22, 23]. Periodate itself is unstable and decomposes over time to form radicals, especially in the presence of light. Oxidations are therefore preferentially carried out in the dark and in the absence of oxygen, using freshly prepared periodate solutions. Also, small amounts of trace metals should be removed as they can also catalyse the formation of free radicals. It has been demonstrated that presence of free radical scavenges such as 1-propanol reduces the extent of depolymerization, and it has therefore been routinely added during oxidation, typically at concentrations around 10 % (v/v) [16]. 

The discussion of this somewhat heterogeneous collection of free and substituted dicarbonyl carbohydrates will be divided into (a) dialdehyde compounds, (b) keto-aldehyde compoimds having free or substituted carbonyl groups, and (c) the diketo compounds. Each Section (except the last one, containing only a few members) will be divided into (a) an introduction consisting of a general discussion concerning formation and preparation, (b) a description of individual compounds, and (c) a discussion of properties and reactions. A short discussion on oxidized polysaccharides is included before the Tables of dicarbonyl carbohydrates and their derivatives. 

The second furan derivative which can be prepared from the appropriate C6 polysaccharides or sugars is hydroxymethylfuraldehyde (HMF). The mechanism of its formation from hexoses is entirely similar to that of F, but difficulties associated with the recovery of the product have delayed its industrial production, despite, again, the ubiquitous character of its natural precursors. A very substantial effort has been devoted in recent years to investigate and optimize novel processes and/or catalysts [36] and the ensuing results suggest that HMF will be a commercial commodity very soon. Interestingly, because of its relative fragility, some of these approaches consider the in situ conversion of HMF into its very stable dialdehyde (FCDA) or diacid (FDCA) derivatives. 

Preparations of pancreatic ribonuclease, ribonuclease from Actinomyces rimosus, and the nuclease from Serratia marcescens have been covalently bound to 4 3-hydroxyethylsulphonylanisole-, 4j3-hydroxyethylsulphonylaniline, and 3-Cl-2-hydroxypropyl derivatives of dextran and dialdehyde-dextran and to the 4-aminobenzyloxymethyl ester of dextran.The yield and thermal stability of the modified nucleases depends both on the amount and the character of the functional groups activating the polysaccharide. 

The effect of the use of cell-wall-degrading-enzyme preparations during the mechanical extraction process of virgin olive oil on the phenolic compoimds and polysaccharides have been investigated. The use of the enzyme preparations increased the concentration of phenolic compoimds in olive oil. Especially, the contents of secoiridoid derivatives such as the dialdehydic form of elenolic acid linked to 3, 4-dihydroxyphenylethanol (3, 4-DHPEA-EDA)... 

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