Melezitose dihydrate

The following description is taken from the comprehensive measurements of Wherry on melezitose dihydrate. 

Angle-table for Melezitose Dihydrate, CisHjiOu-2HjO System, rhombic, seemingly holohedral, but no doubt bisphenoidal Axes a bzc = 1.216 1 0.496 (Data of Wherry )... 

Most of the values reported for the specific rotation of melezitose lie between [qQd +88.1° and +88.8°, as reckoned for anhydrous melezitose by the observers. Richtmyer and the writer48 found [a]D20 +88.5° in water (c, 2) for melezitose monohydrate, CwHjjOu-HaO. Their experience showed that powdered melezitose dihydrate and anhydrous melezitose are transformed rapidly in the air to the stable monohydrate it thus seems doubtful whether the water content of the samples in the older studies was accurately known, and it now appears likely that the samples were essentially melezitose monohydrate. The value [oQn80 +88.5° for melezitose monohydrate corresponds to [a]o 0 +91.7° for anhydrous melezitose, and to [c ]d20 +85.6° for melezitose dihydrate. 

The older data as to the crystallography of the trisaccharide melezitose are not only incomplete but contradictory. Villiers described it as monoclinic, bounded by a prism, m, the base p, and the side pinacoid he obtained the angles g1-.m = 136° 38 and m p = 92° 40. On the other hand Alekhine8 found it to be rhombic, his crystals showing front and side pinacoids, o and a, prism, m, and front and side domes, od and ga, although he recorded no measurements at all. In both cases the dihydrate is supposed to have been represented, but no information has been available to indicate whether this was a case of dimorphism or whether the two authors were in fact not dealing with the same substance. 

CieHa Oiy, Melezitose monohydrate, 42B, 334 CieHasCiBr Planteose dihydrate, 38B, 446... 

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