Carbohydrates solvent precipitation

Commercial lecithin is insoluble but infinitely dispersible in water. Treatment with water dissolves small amounts of its decomposition products and adsorbed or coacervated substances, eg, carbohydrates and salts, especially in the presence of ethanol. However, a small percentage of water dissolves or disperses in melted lecithin to form an imbibition. Lecithin forms imbibitions or absorbates with other solvents, eg, alcohols, glycols, esters, ketones, ethers, solutions of almost any organic and inorganic substance, and acetone. It is remarkable that the classic precipitant for phosphoHpids, eg, acetone, dissolves in melted lecithin readily to form a thin, uniform imbibition. Imbibition often is used to bring a reactant in intimate contact with lecithin in the preparation of lecithin derivatives. 

Polyphenols are ubiquitous in all plant organs where they are found as monomers or in polymerised forms (Schofield et al, 2001). In addition to the beneficial effect of poljq)henols, they also bind minerals and precipitate proteins and carbohydrates, in effect reducing the nutritive value of foods. Polyphenols have been classified for nutritional purposes into extractable and non-extractable types (Bravo, 1998). Extractable polyphenols are low-and intermediate-weight phenolics while non-extractable polyphenols have high molecular weight and are insoluble in normal solvents. 

For the synthesis of carbohydrate-substituted block copolymers, it might be expected that the addition of acid to the polymerization reactions would result in a rate increase. Indeed, the ROMP of saccharide-modified monomers, when conducted in the presence of para-toluene sulfonic acid under emulsion conditions, successfully yielded block copolymers [52]. A key to the success of these reactions was the isolation of the initiated species, which resulted in its separation from the dissociated phosphine. The initiated ruthenium complex was isolated by starting the polymerization in acidic organic solution, from which the reactive species precipitated. The solvent was removed, and the reactive species was washed with additional degassed solvent. The polymerization was completed under emulsion conditions (in water and DTAB), and additional blocks were generated by the sequential addition of the different monomers. This method of polymerization was successful for both the mannose/galactose polymer and for the mannose polymer with the intervening diol sequence (Fig. 16A,B). 

After precipitation, many adducts may be washed with ethanol, and allowed to dry at room temperature. However, consideration must be given to the fact that, if contact of the adduct with the washing solvent is unduly prolonged, washing with ethanol can lead to a reduction in the number of molecules of hydration and, possibly, to a change in the molar ratio of carbohydrate to salt. 

This procedure is often used when the extraction solvent chosen has been water alone, since in this case polar compounds such as salts and amino acids may contaminate the extract. Precipitation with an appropriate solvent, e.g., a mixture of acetate buffer/acetonitrile (22), is then required. Water-soluble macromolecules also interfere and may be removed to a considerable extent by simple precipitation with an organic solvent, for example, ethanol. Nevertheless this may be troublesome, since a proportion of the carbohydrates of interest may become absorbed to the precipitated material, which will be subsequently lost. On the other hand, the sugars must be sufficiently soluble in the solvent used to avoid its precipitation from the solution. 

A further method applicable to benzene-insoluble carbohydrates involves the addition of the compounds, in water, to triphenylboroxin8 (preferably in methanol23), and, under these conditions, some boronic esters have been found to precipitate. Otherwise, the reactants may be fused under vacuum7 (a procedure not in current use, and not recommended) or treated in such solvents as acetone,9,23,24 or 2-methoxyethanol.25,28 Particularly for the formation of nucleoside boronates, pyridine has often been used as the solvent, and the reactants have been heated at the boiling point, or in sealed tubes27-30 on occasion, N,N-dimethylformamide28,31 has been employed. A feature of the use of pyridine is the occasional isolation—not surprisingly—of the products as pyridine complexes.32... 

Several extraction techniques have been reported in the literature for the analysis of sulfonamides. Because of their polar nature, sulfonamides are readily extracted by organic solvents ° ° the most commonly used are acetonitrile.Other organic solvents used for analyte extraction and protein precipitation include dichloromethane, " acetone, ethanol, chloroform, and ethyl acetate, " which are often used either alone or in conjunction with one another. Other techniques used for protein precipitation include the use of acids such as perchloric or formic and the use of basic buffers such as potassium hydrogen phosphate and ammonium sulfate. In the case of honey, the use of acids such as trichloroacetic, " " hydrochloric, and phosphoric is necessary for hydrolysis, releasing carbohydrate-bound sulfonamide residues. Other extraction techniques reported in the literature include the use of pressurized liquid extractions, " matrix solid-phase dispersion, and magnetic molec-ularly imprinted polymers. Of additional note, several authors have observed that analyte recoveries were largely... 

Efficient enzymatic conversion can be achieved even though most of the reactants are present as solids, provided that there is a liquid phase in which the reaction can occur. This approach has been successfully used for carbohydrate ester synthesis with synthesis of glucose esters of fatty acids between C12 and C18 as typical examples [34]. It is important that the substrates dissolve during the reaction, and often the products precipitate as they are formed, which can be an advantage due to a favourable effect on the equilibrium position. Candida antarctica lipase B is an efficient catalyst in this system and solvents used (in moderate amounts) include ethyl methyl ketone, acetone or dioxane. In order to increase the ester yield, water formed in the reaction can be removed by azeotropic distillation and the solvent (e.g. ethyl metyl ketone) can after condensation be dried by pervaporation, giving a practically useful complete process [35]. 

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