Mutarotation sugar solutions

These investigations all point very strongly to the need for placing greater emphasis on the equilibria present in mutarotating sugar solutions when these solutions represent the sugar source in reactions normally expected to require free carbonyls for their accomplishment. 

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). ... 

The course of the mutarotation reactions, the solubilities, and other properties of sugar solutions indicates that equilibrium solutions of... 

The absence of a substantial proportion of the aldehydrol in aqueous sugar solutions shows that the ring forms are far more stable than the aldehydrols. Formation of the aldehydrol requires introduction of a hydroxyl group from the solvent The observation that exchange of 0 is slower than the mutarotation reaction at low temperatures " shows that solvation of the acyclic form is slower than ring interconversion. 

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... 

Pigman, Ward, and Isbell, Horace S., Mutarotation of Sugars in Solution Part I. History, Basic Kinetics, and Composition of Sugar Solutions, 23, 11-57... 

Ferlin, A. S., Action of Lead Tetraacetate on the Sugars, 14, 9-61 Perlin, a. S [Obituary of] Clifford Bur-rough Purves, 23, 1-10 Phillips, G. O., Photochemistry of Carbohydrates, 18, 9-59 Phillips, G. O., Radiation Chemistry of Carbohydrates, 16, 13-58 Pigman, Ward, and Isbell, Horace S., Mutarotation of Sugars in Solution Part I. History, Basic Kinetics, and Composition of Sugar Solutions, 23, 11-57... 

The values given in the table are for the equilibrium mixture in the case of a sugar which undergoes mutarotation. For rapid attainment of equilibrium, add a trace of ammonia to the sugar solution. For practical details, reference shoiild be made to books of practical physical chemistry. 

Mutarotation of sugars in solution. Part I. History, basic kinetics, and composition of sugar solutions, W. W. Pigman and H. S. Isbell, Adv. Carbohydr. Chem., 23 (1968). 

However, the pattern is complicated by several factors. The sugar molecules to be hydrogenated mutarotate in aqueous solutions thus coexisting as acyclic aldehydes and ketoses and as cyclic pyranoses and furanoses and reaction kinetics are complicated and involve side reactions, such as isomerization, hydrolysis, and oxidative dehydrogenation reactions. Moreover, catalysts deactivate and external and internal mass transfer limitations interfere with the kinetics, particularly under industrial circumstances. 

Often, the sweetness of simple sugars is reported in the literature without any indication of anomeric specification, although the values recorded in some cases refer to an equilibrated solution. In other instances, they refer to some unstated, partially mutarotated solution. 

Hexokinase is of great biological interest since it would appear that not only in yeast cells but in most, if not all, plant and animal cells phosphorylation at C6 of the common hexoses D-glucose, D-fructose and D-mannose initiates sugar utilization. Since on solution in water the crystalline hexoses quickly undergo mutarotation, resulting in an equilibrium mixture of various tautomeric modifications, the fermentability... 

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