Mannose specific rotation

Taxon Botanical name Species Yield D-Mannose to of gum D-galactose (%) ratio Specific rotation at 589 nm (degrees) Comments Refer- ences... 

D-Mannose to Specific rotation Specific rotation Refer-... 

Hess and coworkers53 have isolated mannose-containing polysaccharides from both ivory nuts and from pine wood pulp, and these mannans appeared to have identical properties. Both gave specific rotations of approximately —45° in N sodium hydroxide and +285° in cuprammonium (0.04 mole hexose anhydride, 0.10 mole copper, 10.0 moles ammonia per liter). The exact composition of these polysaccharides is not known Yundt54 has recently stated that mannan A from ivory nuts assayed only 50 percent mannose. The cuprammonium rotation data cannot be interpreted in terms of the fine structure until the composition of the mannans is known with certainty. 

D-Mannose exists entirely in pyranose forms. The specific rotation for the a-anomer is +29, and that for the /3-isomer is — 17. The rotation of the equilibrium mixture is +14. Calculate the percentages of each anomer in the equilibrium mixture. 

An apparently similar type of mannan is formed exocellularly by a certain Rhodotorula species. Rhodotorula glutinis mannan has a specific rotation of —78°, and consists of a linear chain of at least 90 units, which is overoxidized somewhat with periodate, consuming 0.61 mole of oxidant with formation of 0.07 mole of acid per mole of mannose residue after two days. Partial hydrolysis gives 4-0-)3-D-mannopyranosyl-D-mannose and 0-j8-D-mannopyranosyl-(1 3)-0-/8-D-mannopyranosyl-(1 4)-D-mannose, but a)8-D-(l- 4)-linked manno-triose is not detectable. Since 2-0-j8-D-mannopyranosyl-D-erythritol is obtained from the mannan by a Smith degradation, an alternating ar-... 

Thirty grams of a polysaccharide containing only n-mannose and D-glucose were acid hydrolyzed. The hydrolysate was diluted to lOOml. The observed rotation of the solution was +9.07 in a 10 cm polarimeter tube. Calculate the ratio of D-mannose/n-glucose in the polysaccharide. The specific rotations of a/j8-D-glucose and a/j8-D-mannose are +52.7 and + 14.5°, respectively. 

When a chloroform solution of hexaacetyl-4- 8-D-glucosyl-D-mannose methyl 1,2-orthoacetate was treated with hydrogen chloride, a rapid change in rotation occurred in that the initial specific rotation of —12.7 became constant in six minutes, [ajo -f29.8 . This change in rotation was similar to that observed with alcoholic solutions. On evaporation, the chloroform solution gave a dextro-rotatory heptaacetyl-4- 8-D-glu-cosyl-D-mannosyl chloride with the structure of the common type of acetylglycosyl halides. 

The nature of the hexose residues and inter-residue links is evident from the results of methylation studies, the preponderant sugars obtained after methylation and hydrolysis being 2,3,6-tri-O-methyl-D-glucose and 2,3,6-tri-O-methyl-D-mannose. The low specific rotation of the glucomannans indicates that the hexose residues occur in the jS-D modification. This is also clear from the nature of the above two disaccharides, as well as from... 

D-mannose residues, and D-mannosidic linkages are more readily hydrolyzed by acids than are D-glucosidic bonds. The high content of D-mannose reported in one study must have been caused by the isolation procedures used, because two other reports agree on the more usual ratio of l 2.5-3.0 for this polysaccharide. The average specific rotation in aqueous alkali is — 38 2°. 

Mannose has three species in equilibrium a-mannopyranose, the aldehyde form, and P-mannopyranose. The position of this equilibrium can be measured, so it is possible to determine the relative percentage of these three species. This discussion must begin with an assumption, however. Assume that the open-chain aldehyde form of mannose (21) accounts for less than 1% of the equilibrium (for most sugars in this chapter, it is about 0.1-0.5% or less) therefore, the pyranose forms are the major conformations. Because these are chiral compounds, one way to measure the equilibrium is to measure the specific rotation (see Chapter 9, Section 9.2). The experimentally measured specific rotation for a pure sample of a-d-mannopyranose (37) is -1-29.3°. The experimentally measured specific... 

The specific rotations for a-D-mannose and p-D-mannose are -1-29.3° and -17.0°, respectively. When either of these monosaccharides is dissolved in water, the rotation reaches an equilibrium value of -I-14.2. Calculate the percentage of the a-anomer present at equilibrium. Show your calculations. 

The a-furanose (0.6%) and p-furanose (0.3%) forms of o-mannose and the P-furanose form (0.14%) of D-glucose have been detected in aqueous solutions by taking advantage of the high resolving power of n.m.r. spectroscopy. The tautomeric forms adopted by ketoses and their biologically important phosphoric esters at equilibrium have also been discussed. The proportion of carbonyl form present in the equilibrium mixture of each of 23 aldoses and 10 ketoses has been estimated from the c.d. spectrum obtained with a highly sensitive circular dichro-meter. An attempt to calculate the probable specific rotations of a- and P-d-fructofuranose is mentioned in Chapter 21. ... 

The [a] of the aandP anomers of D-mannose are+20.3° and-17.0°, respectively. In water, mutarotation of D-mannose results in a specific rotation of+14.2. Disregarding the furanose forms present (<1%), calculate the percent of the... 

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