Sugars hydrophobicity

Alternatively, enzymatic catalysis can proceed in a solventless mixture of substrates. As mentioned above, this method rehes on the esterification of hydrophobic sugar derivatives with fatty acids under solvent-free conditions to overcome the problem of poor solubility of the sugar [7,49,50]. Several methods have been proposed in the literature to overcome this, including acetalization [49,51], complexation of sugars and polyols to phenylboronic acid [52], and alkylation [50,53] of the sugar. Hydrophobization is particularly useful for disaccharides as these are difficult to solubilize in solvents that maintain enzyme activity. 

Breslow studied the dimerisation of cyclopentadiene and the reaction between substituted maleimides and 9-(hydroxymethyl)anthracene in alcohol-water mixtures. He successfully correlated the rate constant with the solubility of the starting materials for each Diels-Alder reaction. From these relations he estimated the change in solvent accessible surface between initial state and activated complex " . Again, Breslow completely neglects hydrogen bonding interactions, but since he only studied alcohol-water mixtures, the enforced hydrophobic interactions will dominate the behaviour. Recently, also Diels-Alder reactions in dilute salt solutions in aqueous ethanol have been studied and minor rate increases have been observed Lubineau has demonstrated that addition of sugars can induce an extra acceleration of the aqueous Diels-Alder reaction . Also the effect of surfactants on Diels-Alder reactions has been studied. This topic will be extensively reviewed in Chapter 4. 

Erodings of Slow-Releasing Core Tablets. The sustained-dose portion of a dmg is granulated with hydrophobic materials such as waxes, fatty acids, or fatty alcohols and compressed into a core. The initial dose is added to the core by a modified sugar coating process or by compression coating. Thus, a tablet within a tablet is created. The core erodes slowly to release the active ingredient. 

Lecithin (qv), a natural phosphoHpid possessing both hydrophilic and hydrophobic properties, is the most common emulsifier in the chocolate industry (5). The hydrophilic groups of the lecithin molecules attach themselves to the water, sugar, and cocoa soflds present in chocolate. The hydrophobic groups attach themselves to the cocoa butter and other fats such as milk fat. This reduces both the surface tension, between cocoa butter and the other materials present, and the viscosity. Less cocoa butter is then needed to adjust the final viscosity of the chocolate. 

The mechanism of the lysozyme reaction is shown in Figures 16.36 and 16.37. Studies using O-enriched water showed that the Ci—O bond is cleaved on the substrate between the D and E sites. Hydrolysis under these conditions incorporates into the Ci position of the sugar at the D site, not into the oxygen at C4 at the E site (Figure 16.36). Model building studies place the cleaved bond approximately between protein residues Glu and Asp. Glu is in a nonpolar or hydrophobic region of the protein, whereas Asp is located in a much more polar environment. Glu is protonated, but Asp is ionized... 

Later, surface-acting polyglucosides were created. These sugar-based detergents are easily broken down by microbes, leaving no traces in the environment. They consist of a pair of glucose molecules, with hydrocarbon side chains attached to act as the hydrophobic ends. They are milder than soaps, and they work in hard water. 

C-18 Sep Pak cartridges have become popular because of their ease of use and high efficiency for fractionating anthocyanins. In an aqueous phase, anthocyanins and other hydrophobic compounds are bound while more hydrophilic compounds such as acids and sugars can be washed away with water. The water can be slightly acidified with 0.01% HCl to stabilize the anthocyanins on the C18 resin. ... 

Figure 17.3 Anatomy of a redox enzyme representation of the X-ray crystallographic structure of Trametes versicolor laccase III (PDB file IKYA) [Bertrand et al., 2002]. The protein is represented in green lines and the Cu atoms are shown as gold spheres. Sugar moieties attached to the surface of the protein are shown in red. A molecule of 2,5-xyhdine that co-crystallized with the protein (shown in stick form in elemental colors) is thought to occupy the broad-specificity hydrophobic binding pocket where organic substrates ate oxidized by the enzyme. Electrons from substrate oxidation are passed to the mononuclear blue Cu center and then to the trinuclear Cu active site where O2 is reduced to H2O. (See color insert.)...

It is also becoming more common to combine IEC with other chromatographic methods to optimize glycoprotein characterization. Takahashi160 has developed a three-dimensional sugar mapping technique utilizing three different HPLC columns a DEAE column, a hydrophobic octadecylsilica... 

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