Monomers sugar

The complete elimination of functional groups is often an undesirable side reaction in organic synthesis, but on the other hand it is a possibility for the recycling of environmentally harmful compounds, for example phenols and haloarenes such as polychlorinated dibenzodioxins (PCDDs or dioxins ). For example, aryl chlorides can be effectively dechlorinated with Pd(0) NPs in tetra-butylammonium salts with almost quantitative conversions also after 19 runs (entry H, Table 1.4) [96]. On the other hand, a C-0 bond cleavage reaction also seems suitable for the fragmentation of sugar-based biomass such as cellulose or cello-biose in that way, sugar monomers and bioalcohol can be derived from renewable resources (entry F, Table 1.4) [164]. 

Figure 12.3 Structures of the nine natural mammalian sugar monomers.

Figure 47 Some of the sugar monomers which make up the hemicellulose polymers.

Monomers and polymers of carbohydrates, (a) The most common carbohydrates are the simple six-carbon (hexose) and five-carbon (pentose) sugars. In aqueous solution, these sugar monomers form ring structures, (b) Polysaccharides are usually composed of hexose monosaccharides covalently linked together by glycosidic bonds to form long straight-chain or branched-chain structures. 

Polymers are large molecules formed by the repetitive bonding together of many smaller molecules, called monomers. As we ll see in the next chapter, biological polymers occur throughout nature. Cellulose and starch are polymers built from small sugar monomers, proteins are polymers built from amino acid monomers, and nucleic acids are polymers built from nucleotide monomers. The basic idea is the same, but synthetic polymers are much less complex than biopolymers because the starting monomer units are usually smaller and simpler. 

T. Uryu, K. Kitano, and K. Matsuzaki, Ring-opening polymerization of 5,6-anhydro-glucose and 5,6-anhydro-allose derivatives. Effect of substitution or configurational difference at the position of sugar monomers on polymerization behavior, J. Polym. Sci., Part A Polym. Chem., 20 (1982) 2181-2194. 

The polysaccharides in the raw materials need to be hydrolyzed before the sugar monomers canbe fermented to ethanol. Today, enzymatic hydrolysis is regarded as a method with great potential. One major obstacle to overcome is the high cost of cellulolytic enzymes. In 2001, the United States Department of Energy formed a contract with two commercial producers of cellulolytic enzymes in an attempt to achieve a 10-fold decrease in the cost of the cellulolytic enzymes (www.ott.doe.gov/ biofuels/research partnerships.html). 

Furthermore, enzymatic hydrolysis of the corn stover treated under optimal AFEX conditions showed almost 98% glucan conversion and 80% xylan conversion vs 29 and 16% for untreated com stover, respectively (at an enzyme loading of 60 FPU/g of glucan). Unlike acidic pretreatments, AFEX does not generate sugar monomers. The cellulase mixture in our study was developed for hydrolysis of acid-pretreated materials and has about 1% by weight xylanase activity (J. Cherry, personal communication, Nov. 2002). Enzyme cocktails with enhanced xylanase activity would presumably completely hydrolyze AFEX-treated xylans. 

Determination of Degree of Inhibition Caused by Sugar Monomers... 

Chromatographic Analysis of Wood Sugars. This analysis requires acid hydrolysis of the polysaccharide to yield a solution mixture of the five wood sugar monomers, i.e., glucose, xylose, galactose, arabinose, and mannose. The solution is neutralized, filtered. 

There is an anomeric carbon, resulting from the equilibrium between the acychc form and the four cyclic forms of a sugar monomer in solution. These cychc forms are comprised of a five-membered furanose ring and the generally more abundant six-membered pyranose ring. Mutorotation around the anomeric centre converts the a-form into the P-form. 

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