Glucosidic unit

Substrates. The principal use for reactive dyes is dyeing textiles ceUulosics constitute the largest use. Cotton is very nearly pure cellulose, and as such has three free hydroxyl groups per glucoside unit that act as dye sites for reactive dyes. 

Figure 30.5. Proposed oxidation mechanism of glucoside unit by iron phthalocyanine-H202 system.

Theoretical calculations demonstrated that the energy gap between HOMO and LUMO levels is not particularly affected by pH variations, but a systematic downshift is recorded with increasing pH. The energetic levels are not influenced by the substituent, which is usually a glucosidic unit, even though has been widely demonstrated that it increases dye stability [34]. 

Exercise 20-14 Explain how the /3-D-glucoside units of cellulose produce a polymer with a stronger, more compact physical structure than the a-D-glucose units of starch. Models will be helpful. 

Mono-altro-/ -CyD was selectively sulfonylated by 2-naphthalenesulfonyl chloride at the 2A-0H of the altrose residue. By using 1-naphthalenesulfonyl chloride as reactant, the 3G-OH of the neighboring glucose became available for selective sul-fonylation [95]. Secondary imidazole-appended fi-CyD, with a nondistorted cavity built of glucoside units synthesized from the novel intermediate 3-amino-) -CyD, exhibits much greater catalytic activity in ester hydrolysis than its isomer with the distorted cavity obtained from altroside units [96]. 

Fig. 22 a UV absorption spectra of the hexane layer after the treatment with aqueous layers containing different amounts of s-SPG and b Estimated percentages of PMDS extracted from the hexane layer into the aqueous one pathlength 5mm, 25 °C, [PMDS] = 0.431 mM (an original concentration in the hexane layers), [s-SPG] = 0.0-3.5mM (0.0-8.0eq., an original concentration in the aqueous layers) based on their repeating units (four glucoside units for SPG and one dimethylsUane unit for PMDS). Reprinted with permission from [118]... 

Structure analysis. Dextrans constitute a group of polysaccharides composed essentially of a(1- 6) linked glucoside units with a low proportion of branching (figure 1). they are produced by micro-organisms. Many different strains of bacteria exist which can enzymatically convert sucrose or starch to dextran. ... 

From this data it was calculated that the dextran used contains 10% irregularities. Moreover, from the close agreement between the observed periodate consumption and that calculated from the formic acid production, it may be concluded that these irregularities can be assigned as linked glucoside units. Khomyakov concluded from periodate oxidation studies on dextrans, synthetized by Leu-conostoc mesenteroides species, that in addition to a(l- 6) linkages a certain number of l->-3 and links were present. However... 

Due to its large availability and low cost, native starch has been used for a long time in the preparation of different end-products. To obtain specific properties, native starch has to be chemically or enzymatically modified. Because native starch is an insoluble, partially crystallized solid polymer, chemical modifications are difficult to achieve and require the use of soluble catalysts. We have achieved two catalytic modifications of native starch (i) selective oxidation to obtain carboxyl and carbonyl functions, thus making starch more hydrophilic (8), and (ii) telomerisation of butadiene with the hydroxyl groups of the glucoside units, thus providing more hydrophobic material (8,9). 

On hydrolysis, cellulose yields glucose exclusively, and w hen acetylated and hydrolysed simultaneously (acetolysis) it yields 50 per cent, of cellobiose (4-)S-gluco8ido-glucose), which indicates that cellulose is a chain of -glucosidic units. 

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