The simple carbohydrates and the glucosides / by E. Frankland Armstrong.

  • Edward Frankland Armstrong
Date:
1910
Catalogue details

Licence: In copyright

Credit: The simple carbohydrates and the glucosides / by E. Frankland Armstrong. Source: Wellcome Collection.

    23/132 (page 7)
    The subject assumed a new aspect when it was shown by Tanret in 1806 that besides the anhydrous and hydrated forms of glucose other isomeric anhydrous modifications could be obtained. He described an a-glucose ([a]D + 110°), the initial rotatory power of which fell grad- ually to [a]D+ 52-5°; further, a /3-glucose1 of low initial rotatory power ([a]D+19°), increasing to [a]D+52‘5° in solution; and, lastly a 7-glucose ([«]„+ 52-5°) of unalterable rotatory power in solution. Ihe three supposed isomerides were isolated by allowing glucose solutions to crystallise under different conditions—a-glucose separated at or- dinary temperatures from solutions in 70 per cent, alcohol, and /9-glucose from aqueous solutions at temperatures above 98 C.; 7-glucose was obtained by precipitating a concentrated aqueous solution of glucose with alcohol, a-glucose hydrate crystallises from aqueous solutions at the ordinary temperature. When powdered anhydrous glucose is added to water, it immediately undergoes hy- dration before passing into solution. The behaviour of these isomeric forms does not fit in with the theory that the mutarotation is due to the conversion of an aldehyde into an aldehydrol; moreover, the increase in rotatory power from /3- to 7-glucose has also to be explained. Tanret, Lippmann and others suggested that some forms of glucose have a closed-ring structure, as proposed by Tollens, and that in solu- tion these are completely converted into the isomeric aldehyde. A more fruitful suggestion was made by Simon who drew atten- tion to the optical behaviour of a- and /3-glucose in relation to that of the isomeric methyl glucosides of which the structure was known [a]D 0]d a-Methyl- glucoside + 157° a-Glucose + 105° /3-Methyl- glucoside - 330 /3-Glucose + 220 He suggested that the a- and /3-glucoses are homologues of the a- and /3-methyl glucosides, and that both contain a closed oxygenated ring. Direct proof of the glucosidic structure of a- and /3-glucose was afforded by their preparation from the corresponding glucosides effected by the writer. Both glucosides are resolved into methyl alcohol and glucose by appropriate enzymes, and as the enzymes condition the hydrolysis more quickly than the glucose which is formed can undergo isomeric change, it is possible to determine the nature of the sugar which is formed initially. In practice, this is done by preparing a clear solution of glucoside and enzyme, allowing hydrolysis to proceed 1 Tanret actually termed the substance represented above as /8-glucose 7-glucose and designated y-glucose as /3-glucose. The terms have been altered to bring them into agree- ment with the nomenclature now adopted.