Composition of sugars

Part I. History, basic kinetics, and composition of sugar solutions, 23, 11-57... 

Although most of these forms of sugars have never been isolated, they can be detected in the n.m.r. spectra of the sugars, and their proportion in the equilibrium mixture can be measured. Before the advent of n.m.r. spectroscopy, only a rudimentary knowledge of the composition of sugars in solution was available, but, since 1961, an extensive collection of data has been built up, mainly by the use of n.m.r. spectroscopy. These data are the subject matter of this article. The composition of sugars in solution was reviewed3 in 1969, but since then, much new information has been accumulated. 

Knowledge of the composition of sugars in solution is fundamental to carbohydrate chemistry. The physical and chemical properties of the sugars in solution depend on the proportions of their various forms and their biological properties may also show such dependence. Enzymes that utilize these sugars as substrates may not be able to use each of the forms. Where only a single form is utilized, the other forms may either be converted into the reactive form or may function as inhibitors. The latter is especially important if the reactive form is present in very low proportion at equilibrium. It is possible that the substrate form is utilized faster than it is generated from the other forms the observed rate of the reaction is then that of the tautomeric interconversion.4... 

Dilute acids or bases have no noticeable effect on the composition of sugars in aqueous solution at high concentration, however, they alter it considerably. What is then observed is, in fact, not the equilibrium of the sugars themselves but that of their cations and anions, respectively, sugars being weak bases and weak acids. Thus, the a yj-pyranose ratio for D-glucose in 2,5 M DC1 was found90 to be 45 55 the same ratio was obtained when the solvent was formic acid. 

Water is the only solvent in which the composition of sugars has been systematically explored. Stevens1674 has determined the composition of several aldoses in pyridine-d5 by -n.m.r, spectroscopy at 300 MHz. There are scattered data on solutions in organic solvents (mainly pyridine, dimethyl sulfoxide, and N,N-dimethylformamide), but only rarely have four (or more) components of such solutions been quantitatively determined. The data that have been encountered are collected in Table VII undoubtedly, there are others that have been missed. 

Kuhn and Grassner168 were the first to realize that the solution composition of sugars may vary considerably with a change of solvent. They stated that D-fructose in N,N-dimethylformamide exists in furanose forms to the extent of 80%. (This value is probably too high compare with Table VII.)... 

The composition of sugars in solution varies considerably with changes in the temperature (see Section III,6). It is essential, therefore, to record the temperature at which the proportions have been determined. Ideally, all of the compositions should have been listed at the same temperature, but, unfortunately, different authors have used different temperatures for their measurements. In the Tables, therefore, the temperature at which the data were obtained is recorded where no such figure appears, it was not possible to ascertain this information from the published texts, In those cases where data at several temperatures were published, those recorded closest to 25° are listed. 

For GL-2, the composition of sugars has been determined. Glucose, mannose, xylose, and 3-O-methylfucose were detected,257 and the compound was shown to contain a free amino group and phosphorus, similarly147 to GL-3. 

The question of the detailed composition of sugar solutions in various solvents together with the chemistry of the mutarotation reaction has continued to attract attention through the years. In their classical review, Mutarotation of Sugars in Solution, completed in 1969, Isbell and Pig-man have cited references to more than 320 papers and books (5, 6). The appearance of this volume justifies Isbells faith that carbohydrate chemistry continues to have a significant impact on the development of new concepts permeating all branches of chemistry and biochemistry (7). ... 

During an investigation of the properties of furanoses, Serianni and coworkers6 studied the composition of sugars which cannot form pyranoses. Starting with the aldotetroses6 [p. 36], they studied the 5-deoxypentoses 9 some 5-0-substituted pentoses,9 29 and the 2-pentuloses.12 All these compounds will be discussed in this Section. 

History, Basic Kinetics, and Composition of Sugar Solutions... 

Composition of Sugar Solutions as Determined by Nuclear Magnetic Resonance Measurements ... 

In some instances, nuclear magnetic resonance techniques employing trimethylsilyl ethers have provided information on the composition of sugar solutions that could not be obtained by classical methods. Thus, the formation of D-galactofuranose during mutarotation was shown by gas chromatography of the trimethylsilyl derivatives of D-galactose (from the mutarotation mixture). The products were... 

Calculate the elementary composition of sugar (sucrose), 012 220,1 that is, calculate the percentage of each element in this substance. 

Table 1.2 Tautomeric composition of sugars in D2O according to Angyal (1984 1991) (reproduced with kind permission from Academic Press).

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