Mutarotation and gas-liquid chromatography

By application of first-order, kinetic equations, B. Anderson and Degn claimed that an equilibrated (25°) aqueous solution of D-fructose contains 31.56% of jS-D-fructofuranose and 68.44% of -D-fructopyranose. N.m.r. studies, however, showed that, at equilibrium, a solution of D-fructose contains /3-D-fructopyranose, -D-fructofuranose, a-D-fructofuranose, and a trace of a-D-fructopyranose the distribution of these isomers was shown by gas-liquid chromatography to be 76,19.5, and 4%, respectively. Based on Anderson and Degn s result, Shallenberger reasoned that, as 0.68 X 1.8 = 1.22 (which approximates the reported sweetness of mutarotated D-fructose ), the furanose form(s) must possess very little sweetness. 

The original publication by Sweeley and coworkers5 was concerned with the separation of a wide range of carbohydrates, from mono- to tetra-saccharides. Most of the subsequent publications have considered the quantitative analysis of mixtures of varied complexity, although two studies have demonstrated the separation of the protium from the deuterium fonns of monosaccharides.200,201 The study of mutarotational equilibria by gas-liquid chromatography has been discussed in Section IV (see p. 38). 

In a further quantitative check of the validity of the calculated free-energy values, the predicted a,p anomeric equilibria of the aldopyranoses in aqueous solution were found to be in reasonable agreement with those determined experimentally by studies of their mutarotation, oxidation by bromine, and n.m.r. spectra. In addition, the position of the equilibria between aldohexopyranoses (and 3-deoxy-aIdohexopyranoses) and their 1,6-anhydrides, and between heptuloses and their 2,7-anhydrides, as determined by gas-liquid chromatography, were in good agreement with data estimated from conformational interaction-energies. 

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