Carbohydrates, estimation reactions

The aromatic nature of lignin contrasts with the aliphatic stmcture of the carbohydrates and permits the selective use of electrophilic substitution reactions, eg, chlorination, sulfonation, or nitration. A portion of the phenoUc hydroxyl units, which are estimated to comprise 30 wt % of softwood lignin, are unsubstituted. In alkaline systems the ionized hydroxyl group is highly susceptible to oxidative reactions. 

Add to the solution a 50-fold molar excess of BAP over the estimated amount of carbohydrate present in the reaction mixture. 

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... 

Carbohydrates, whose continental and marine productions have been estimated at nearly 1011 and 10 t/year respectively (42), have qualified for recognition as a possible carbon source. Indeed, the treatment of carbohydrate with hydrogen sulfide at a temperature as low as 100 °C is reported to result in S-heterocycle formation (43). Recently, glucose has been treated with hydrogen sulfide at 40 °C then pyrolyzed in the course of product analysis. Although S-heterocycles were found in the pyrolysate (44), the conditions to which the carbohydrates were subjected may result in their conversion to the proximate carbon source, which only then is sufficiently reactive enough to combine with hydrogen sulfide. Thus, the role assumed of carbohydrates as proximate carbon source molecules in low-temperature reactions is presently not readily appraised. 

The structured model is consistent with features of lytic enzyme action and yeast structure reported in the literature. The sequential removal of the two wall layers, followed by protoplast rupture, accurately describes the early lag in protein and carbohydrate release. The presence of residual solids at long reaction times was accounted for stabilization of protoplasts by substances released from lysed cells. The structured model can be used to estimate the effects of several process alternatives, as shown in a simulation of a process for recovery of site-linked enzymes from yeast. 

Similarly the estimation of pentoses with phloroglucinol is unreliable when the hexose to pentose ratio is >10 1 (Selvendran et al., 1979), and hexuronic acids also contribute to the color yield (Jermyn and Isherwood, 1949 Selvendran and DuPont, 1984). It is possible to correct for such interfering reactions but this requires a prior knowledge of the carbohydrate composition of the material. 

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