Galactose specific rotation

Test the purity of the galactose prepared by determining the specific rotation with a polarimeter. An aqueous solution containing one gramme of substance in 10 c.c. should have a rotation of +845° in a decimetre tube. Hence [a] °° = + 81-50. 

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

P. A. Levene and F. B. LaForge, J. Biol. Chem., 20, 429 (1915). These workers give an [< ]d value of +0.80° —> +0.34° (c, 2 I, 0.5) for the phenylosazone from D-galactose the solvent being pyridine (2 parts) + ethanol (3 parts). However, it is obvious from the context of their article that these values refer to observed rotations and that the actual specific rotations [[Pg.134]

The myxomycete Physarium polycephalum produces hard-walled sclerotia (spherules) that contain 88% of 2-amino-2-deoxy-D-galactose. The positive, specific rotation, and the g.l.c. characterization of 1,5-di-... 

Like glucose, galactose mutarotates when it dissolves in water. The specific rotation of a-D-galactopyranose is +150.7°, and that of the 13 anomer is +52.8°. When either of the pure anomers dissolves in water, the specific rotation gradually changes to +80.2°. Determine the percentages of the two anomers present at equilibrium. 

An aqueous solution of D-galactose has an [a]o of +80.2° after standing for some hours. The specific rotations of pure a-D-galactose and -D-galactose are +150.7° and +52.8°, respectively. Calculate the proportions of a- and -D-galactose in the equilibrium mixture. 

The yields vary considerably, even for the same species. It should, however, be remembered that larch heartwood apparently contains much more arabinogalactan than does the sapwood, that the lower portion of the trunk is reported to yield more material than the upper, and that the content of arabinogalactan in the tree may well vary with the time of year. The ratio between galactose and arabinose residues also varies considerably, although there is no general difference as between the different species. It is evident that the wood is usually richer in arabinogalactan A than in B. Where no separation of these two components was undertaken, a molar ratio of galactose to arabinose of 5 to 6 1 is most common. The specific rotation is low and positive, with no evident difference between the two fractions. 

A summary of the yields obtained and the chemical properties of the arabinogalactans of this type so far investigated is presented in Table X. Even before purification, the yields, throughout, are very low. The ratio of D-galactose to L-arabinose varies widely, with no noticeable trend with respect to species, and the same is true of the specific rotations. 

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