Glucose, <7 anomer

Figure 1. Gas chromatography of the TMSi derivatives of the glucose anomers.

When samples of a pure glucose anomer were dissolved in water and a sample removed for silylation within about 30 seconds, only one major peak was obtained, and the chromatogram was indistinguishable from that obtained by treatment of the solid anomer with the standard silylation reagent. Occasionally, minor peaks were present, preceding the peak of the a anomer these may have represented partial trimethyl-silyl derivatives (28). 

The glucose anomers have interesting taste characteristics. As mentioned before, by their behavior in solution, one could conclude that either the < -d or the / -D-anomer is sweeter. What this information... 

Hill, J. B., Mutarotase and Glucose Anomers, Parts I and II, Biochem. 

An ab initio calculation with a minimal basis set of both a- and 0-glucopyranose as well as p-maltose results in the correct prediction of the energetical order of the two glucose anomers as well as the two conformations of p-maltose [80], But the less favored conformer contains an energy which is higher by a factor of approximately 6 compared to the results of the FF300 calculation (cf. below). 

Figure 1.13 The mutarotation of glucose anomers. The specific rotation of the aqueous equilibrium mixture is +52°...

Figure 9.4 Chair forms of glucose anomers. Note that the -OH group on the anomeric carbon (carbon 1) is axial (less stable) in a-D-glucopyranose, whereas it is equatorial in (3-D-glucopyranose. Mutarotation therefore favors the latter.

In Table 7.11, we list the results of four computational studies that address the glucose anomer population in solution. All four studies use a number of conformers of each anomer and treat the solvent with either SM or PCM. As with their prediction for gas-phase populations, these four methods are generally in good agreement the MP2 results again appear to overestimate the a population. 

Hydrolysis of maltose forms two molecules of glucose. The Cl - O bond is cleaved in this process, and a mixture of glucose anomers forms. The mechanism for this hydrolysis is exactly the same as the mechanism for glycoside hydrolysis in Section 27.7B. 

Draw a stepwise mechanism for the acid-catalyzed interconversion of two glucose anomers by mutarotation. 

Figure 20. C-NMR spectra from a perfused mouse liver at SS C. (c) C natural abundance background of this liver, accumulated before the substrate was added. The substrate, 8 mM [3- C]alanine and 20 mM unlabelled ethanol, was then added at 0 minutes and again at 120 minutes, and a series of C-NMR spectra were taken, (b) Spectrum measured during the period 150-180 minutes (a) C-NMR spectrum of the perfusate after the perfusion was terminated, at 240 minutes this spectrum consisted of 5000 scans. The pulse repetition times were 0.5 seconds for b and c and 2 seconds for a. Abbreviations pci, oCl, ]9C3.5, aC4, pC6, aC6, PC2, C2.5 and aC3, the carbons of the glucose anomers Glu C2, glutamate C-2 Gin C2, glutamine C-2 Asp C2, aspartate C-2 Ala C2, alanine C-2 LacC3, lactate C-3 CB, cell background peak W, X, Y and Z, unknowns AA Ca, acetoacetate CHj and / -HB Ca, -hydroxybutyrate CHj (from [31]).

ATP-dependent hexokinase (HK, EC 2.7.1.1) converts both glucose anomers. Its Km for glucose is 10 mmol/1. The tetrameric protein (MW 100 000) contains eight SH-groups per molecule, of which four are essential for the enzyme s function. Owing to the high specificity of HK, glucose determination by means of this enzyme has become the inter-... 

The modeled transition-state structures for hydrolysis by the a-glucosi-dase and the glucoamylase show significant oxocarbonium ion character with the D-glucosyl unit of each having a flattened 4C conformation consistent with a C-l-O-5 bond order of 1.92, even though opposite o-glucose anomers are formed from the substrate. The transition-state structures show modest differences but they do not predict the stereochemical outcome of the catalyzed reactions.157... 

This study shows that 2-D NMR analysis of intact EC can provide structural information, such as confirming the presence of cellulose ethoxylated at the C3 position, but does not readily yield quantitative information such as positional DS. 2-D NMR analysis of TFA-hydrolyzed EC confirms formation of a complex mixture of ethoxylated a and p- glucose anomers. A combination of HMQC and HMBC analyses was used to confirm the assignments used for quantitative 1-D C NMR analysis without reference to external standards. Because of improved spectral resolution, HOHAHA analysis of hydrolyzed EC afforded relative positional DS that agreed well with values determined by GC-... 

The D-glucose anomer can form a hydrogen bond between CH2OH group and the equatorial anomeric hydroxyl group, which is not possible with the a anomer. Consequently, the optical activity of jS-D-glucose ([of] = 18.7) is smaller than that of a-D-glucose ([a]f = 112.2). 

Structures 4 and 5 for the glucose anomers are called Haworth formulas and, although they do not give an accurate picture of the shape of the six-membered ring, they have many practical uses. Figure 22.4 demonstrates how the representation of each chirality center of the open-chain form can be correlated with its representation in the Haworth formula. 

Are a-D-glucose and /3-D-glucose anomers Explain. Are they enantiomers Explain. 

At equilibrium, the (3 anomer of D-glucose predominates, because the —OH group of the anomeric carbon is in the more stable equatorial position of the more stable chair conformation. In a-D-glucose, the —OH group on the anomeric carbon is axial. When remembering the names of D-glucose anomers, some students find it helpful to remember the phrase alpha is axial. 

The following are the more stable anomers of the pyranose forms of D glucose D mannose and D galactose... 

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