Monosaccharide solutions

Curey TE, Goodey A, Tsao A, Lavigne J, Sohn Y, McDevitt JT, Anslyn EV, Neikirk D, Shear JB. Characterization of multicomponent monosaccharide solutions using an enzyme-based sensor array. Analytical Biochemistry 2001, 293, 178-184. 

Maltol 337 is one of the degradation products in monosaccharide solutions with amino acids forming Amadori compounds but not in the solution of monosaccharides alone. Heated solutions of monosaccharides yield 335, the logical precursor of 337, but not 337 itself. On the basis of the molecular mechanics calculation indicating that 335 adopts the conformation unfavorable for dehydration into 337, a possible route via the dehydrated product 336, an ortho-elimination product, has been postulated as a more favorable alternate reaction pathway [277]. 

Monosaccharide Solution pyranosc pyranose furanose furanose Reference... 

The internal standard and monosaccharide solutions are added to 2-ml ampoules in varying amounts as shown below ... 

Ampoule No. Internal standard solution OJ) Monosaccharide solution Oil) Mole ratio of each monosaccharide to the internal standards... 

Procedure To a dilute aqueous monosaccharide solution (2 ml) 1-naphthol solution (five drops) is added, and then several milliliters of cone, sulfuric acid are added carefully down the sides of the test tube. A violet or red color is formed on the surface of the sulfuric acid. After mixing, the liquid assumes a dark violet color and after dilution a blue-violet precipitate separates which is soluble in ether with a yellow color. A control experiment is carried out simultaneously without 1-naphthol, as a series of substances gives similar colors with sulfuric acid alone. 

The weights of other monosaccharides and reducing disaccharides which will reduce i ml. of this standard Fehling s solution are galactose, 0 00511 g- fructose. 0 00514 g.. mannose, 0 00431 g. lactose, 0 00678 g. maltose, 0 00807 g. 

Fructose—Dextrose Separation. Emctose—dextrose separation is an example of the appHcation of adsorption to nonhydrocarbon systems. An aqueous solution of the isomeric monosaccharide sugars, C H 2Dg, fmctose and dextrose (glucose), accompanied by minor quantities of polysaccharides, is produced commercially under the designation of "high" fmctose com symp by the enzymatic conversion of cornstarch. Because fmctose has about double the sweetness index of dextrose, the separation of fmctose from this mixture and the recycling of dextrose for further enzymatic conversion to fmctose is of commercial interest (see Sugar Sweeteners). 

Monosaccharides such as glucose and fmctose are the most suitable as starting materials. When starch is used, it is first hydrolyzed with oxahc acid or sulfuric acid into a monosaccharide, mainly glucose. It is then oxidized with nitric acid in an approximately 50% sulfuric acid solution at 63—85°C in the presence of a mixed catalyst of vanadium pentoxide and iron(III) sulfate. 

Sucralose is quite stable to heat over a wide range of pH. However, the pure white dry powder, when stored at high temperature, can discolor owing to release of small quantities of HCl. This can be remedied by blending it with maltodextrin (93) and other diluents. The commercial product can be a powder or a 25% concentrate in water, buffered at pH 4.4. The latter solution may be stored for up to one year at 40°C. At lower pH, there is minimal decomposition. For example, in a pH 3.0 cola carbonated soft drink stored at 40°C, there is less than 10% decomposition after six months. The degradation products are reported to be the respective chlorinated monosaccharides, 4-chloro-4-deoxy-galactose (13) and l,6-dichloro-l,6-dideoxy-fmctose (14) (94). 

The gel-like, bead nature of wet Sephadex enables small molecules such as inorganic salts to diffuse freely into it while, at the same time, protein molecules are unable to do so. Hence, passage through a Sephadex column can be used for complete removal of salts from protein solutions. Polysaccharides can be freed from monosaccharides and other small molecules because of their differential retardation. Similarly, amino acids can be separated from proteins and large peptides. 

In a similar manner, ketones can react with alcohols to form hemiketals. The analogous intramolecular reaction of a ketose sugar such as fructose yields a cyclic hemiketal (Figure 7.6). The five-membered ring thus formed is reminiscent of furan and is referred to as a furanose. The cyclic pyranose and fura-nose forms are the preferred structures for monosaccharides in aqueous solution. At equilibrium, the linear aldehyde or ketone structure is only a minor component of the mixture (generally much less than 1%). 

Some monosaccharides also exist in a five-mem be red cyclic hemiacetal form called a furanose form. D-Fructose, for instance, exists in water solution as 70% /Tpvranose, 2% a-pyranose, 0.7% open-chain, 23% /3-furanose, and 5% a-furanose. The pyranose form results from addition of the -OH at C6 to the carbonyl group, while the furanose form results from addition of the —OH at C5 to the carbonyl group (Figure 25.5). 

Deoxy sugars, as we saw in Section 25.7, have an oxygen atom "missing." That is, an —OH group is replaced by an -H. The most common deoxy sugar is 2-deoxyribose, a monosaccharide found in DNA (deoxyribonucleic acid). Note that 2-deoxyribose exists in water solution as a complex equilibrium mixture of both furanose and pyranose forms. 

The intermolecular interactions stabilise the helices and greatly influence the properties of exopolysaccharides in solution, ie solubility, viscosity and gel-formation. A strong interaction or good-fit between molecules will lead to insolubility, whereas poor interaction will lead to solubility of exopolysaccharides. The interactions between molecules is influenced by the presence of side-chains. For example, cellulose is insoluble but introduction of a three monosaccharide side-chain into the cellulose chain gives the soluble xanthan. Small changes in the structure of the side-chains can alter the molecular interactions and thus properties of the exopolysaccharide. 

The practice of including the conformation after the name of the parent monosaccharide should be used only with caution because not all conformations are known with certainty. In the case of furanose rings especially, conformations might differ between the crystalline and solution states. 

---