Carbohydrates hydrolytic reactions

Starch conversion refers to the process of converting starch into other products. It involves gelatinization, liquefaction, and saccharification. Liquefaction refers to the acid-or enzyme-catalyzed conversion of starch into maltodextrin. Starch, usually from wet milling of com, is pumped in a slurry to the conversion plant, where it undergoes one or more hydrolytic processes to yield mixtures of various carbohydrates in the form of syrups. The kind and amount of the various carbohydrates obtained depend upon the type of hydrolysis system used (acid, acid-enzyme, or enzyme-enzyme), the extent to which the hydrolytic reaction is allowed to proceed, and the type of enzyme(s) used. The fact that most starches consist of two different kinds of polymers... 

Hydrolytic Reactions. Probably the most important reactions, with regard to their impact on the properties of wood, involve some type of hydrolysis. Both carbohydrates and lignin are affected, and hydrolysis is encountered in almost every kind of wood processing. 

The presence of carbohydrate on protein molecules protects them from dena-turation. For example, bovine RNase A is more susceptible to heat denaturation than its glycosylated counterpart RNase B. Several other studies have shown that sugar-rich glycoproteins are relatively resistant to proteolysis (splitting of polypeptides by enzyme-catalyzed hydrolytic reactions). Because the carbohydrate is on the molecule s surface, it may shield the polypeptide chain from proteolytic enzymes. 

Metal-dependent hydrolases are critical in protein, carbohydrate, and nucleotide metabolism. In addition to the intellectual contributions, there is much interest in these hydrolases because many of them are potential targets for drug intervention. Hernick and Fierke detail the physical and chemical properties that make metals suitable for hydrolysis reactions including their Lewis acidity, electronic configuration, and exchange properties. Although a number of metal ions meet these criteria, zinc is most commonly found in metal-dependent hydrolases. Along with amino acid side chains that participate in proton transfer reaction and stabilize reaction intermediates, the presence of the metal ion facilitates the hydrolytic reaction. 

Carbohydrates and proteins may also play an important role in weathering of soils. As much as 30% of the DOC in soil solutions can occur as saccharides, although only a small portion has been accounted for as polysaccharides. Polysaccharides extracted from soil usually contain Al, Fe, and Si an indication of their ability to complex polyvalent ions. Amino acids, peptides, and proteins are also capable of forming complexes with metal ions. These substances have a strong affinity for binding to silicate minerals and are able to perturb the hydrolytic reactions of Al. 

This chapter, therefore, ends the monograph with a potpourri of reactions all of which occur without a change in oxidation state. In many cases, the reaction is one of nucleophilic attack at an electrophilic C-atom. The result is often hydrolytic bond cleavage (e.g., in carbohydrate conjugates, disubstitut-ed methylene and methine groups, imines, oximes, isocyanates, and nitriles, and various ring systems) or a nucleophilic substitution (e.g., hydrolytic de-halogenation of halocarbons and chloroplatin derivatives, and cyclization reactions). The formation of multiple bonds by dehydration is a special case to be discussed separately. 

Galbis et al. described a variety of carbohydrate-based linear polyesters 61 of the poly(alkylene dicarboxylate) type that were obtained by polycondensation reactions of the alditols 2,3,4-tri-(9-methyl-L-arabinitol (9) and 2,3,4-tri-O-methyl-xylitol (10), and the aldaric acids 2,3,4-tri-(9-methyl-L-arabinaric acid (26) and 2,3,4-tri-(9-methyl-xylaric acid (27), butanediol, and adipic acid were also used as comonomers [28]. Copolyesters of the poly(aIkylene-c )-arylene dicarboxylate) type were obtained using bisphenols as comonomers (Scheme 1). Chemical polycondensation reactions were conducted in bulk or in solution. Enzymatic polycondensation reactions of adipic acid with the above-mentioned alditols were carried out successfully using Lipozyme and Novozyme 435. The hydrolytic degradations of some of these polyesters were also described. 

Another carbanilate herbicide, 4-chloro-2-butynyl 3-chlorocarbanilate (barban), formed a water-soluble metabolic product in various plants. The metabolite could not be identified as any simple reaction-product, and it was tentatively proposed that the original herbicide might be associated with a plant component such as a flavonoid. 3-Chloroaniline could be distilled out after hydrolysis, and several hydrolytic fractions contained carbohydrates but no nitrogen.177... 

For the release of an unaltered base, the sugar moiety must be damaged. In principle, the base could already be released from a radical site at the sugar moiety, i.e. on the time-scale of the lifetime of the DNA radicals. The observation of 2-dRL incorporated into DNA as a product formed upon OH attack shows that a damage at C(l ) contributes to the release of an unaltered base. In the carbohydrate series, hydrolytic scission at the glycosidic linkage when this site contains a free-radical is a well-documented phenomenon, and it has been estimated that the rate of reaction must be faster than 35 s 1 (von Sonntag and Schuchmann 2001). As it stands, it cannot be excluded, that under certain conditions the base release from the C(l ) radical [reaction (38)] occurs in competition to its oxidation [reaction (2)]. In a cellular environment, there is also the reduction of DNA... 

Many of the reactions occurring in lipids are oxidative or hydrolytic and their products can further react with primary reaction products of the Maillard reaction occurring between amino acids and carbohydrates. 

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