The Mutarotation of Fructose and the Invertase Hydrolysis of Sucrose

Observation of the keto tautomer of d-fructose in D2O using 1H NMR spectroscopy

“…The pyranose to pyranose transformation is slow, occurring between two stable chair conformations, 1,4,6,7,29 while the transformation between pyranose and furanose is rapid 4 and the furanose-to-furanose transformation is very rapid, occurring essentially instantaneously between relatively high-energy envelope and twist forms. 1,9,12,22,24 Nonetheless, the mutarotation of fructose can often be approximated as a simple first-order process, 4,12 and it has been demonstrated that the kinetics can be represented by the conversion of β-pyranose to the furanose forms. 30 …”

“…Using the tautomeric composition determined by 1 H NMR spectroscopy (discussed further in the following section), the ratio of β-furanose to α-furanose of 4.1:1 was determined to be constant between 5 °C and 50 °C, in close agreement to values in the literature. 12 Consequently, it was possible to use this peak to establish the concentration of furanose forms relative to the total concentration of fructose. The relative concentration of the furanose forms over the course of the mutarotation was plotted and found to rise exponentially, confirming the validity of using first-order kinetics.…”

“…As the free sugar, fructose is an example of a simple reducing sugar that has a complex 1 H NMR spectrum as a result of it existing in at least five tautomers in solution (Figure 1). 4,12–14 At equilibrium in water β-D-fructopyranose (β-pyr) is the preponderant tautomers, followed by β-D-fructofuranose (β-fur), and then α-D-fructofuranose (α-fur). These tautomers have previously been determined to account for 69.6%, 21.1% and 5.7% of the solubilised sugar at room temperature, respectively.…”

“…14 The minor tautomers of fructose are α-D-fructopyranose (α-pyr) and the linear keto form of fructose. 12–16 The keto form of fructose has not been previously identified using 1 H NMR spectroscopy in D 2 O. 11,15,17–19 The α-pyranose tautomer has also been difficult to identify using 1 H NMR spectroscopy in aqueous solution, only being observed in experiments measuring the anomeric hydroxyl group conducted on samples equilibrated in water, flash frozen, and then melted into DMSO- d 6 .…”

Investigating the performance of in situ quantitative nuclear magnetic resonance analysis and applying the method to determine the distribution of saccharides in various parts of carrot roots (Daucus carota L.)

“…All NMR spectra were recorded at 18 1C to avoid changes in the mutarotation equilibrium [54]. For each spectrum, 32 scans of 32 K data points were acquired with a spectral width of 6 Hz, an acquisition time of 5.3 s, and a recycle delay of 25 s per scan to allow complete relaxation and absolute quantification [49]; the pulse angle was 901.…”