Publisher Summary This chapter discusses the composition of reducing sugars in solution. Reducing sugars differ from most other organic compounds in one characteristic property. When a pure organic compound that is not a reducing sugar is dissolved in a solvent, it is certain that the solution will usually contain only one compound; but when a reducing sugar, above an aldotetrose or a 2-pentulose, is dissolved in water, a solution is obtained that always contains at least six compounds: two pyranoses, two furanoses, and an acyclic (open-chain) carbonyl form and its hydrate. There are also minute proportions of septanoses and dimers. Very few of these many compounds that are present in the equilibrium solutions of sugars have ever been isolated. The only method for separating them from the equilibrium mixture is by crystallization and that depends on the fortuitous presence of seed crystals. The chapter details about the pyranose form, the furanose form, and the septanose form. It also discusses the composition of aldoses, ketoses, and substituted and derived sugars in aqueous solution.

The composition of reducing sugars in solution

Publisher Summary The chapter focuses on the methods for determination of conformation of sugars and their derivatives The study of the conformations of organic molecules pointed out that six membered ring-systems can exist free from bond-angle strain, in two puckered forms, the flexible or asymmetric form, and the rigid or symmetric (chair) form Boat or skew conformations are considered possible if the nonbonded interactions between the substituents in the chair conformation are too large The conformational analysis of saturated five and six-membered heterocycles, presenting data relevant to the carbohydrate field, is also presented The various techniques discussed in the chapter are X-ray crystallography andspectroscopic methods—namely infrared spectroscopy, microwave spectroscopy, and nuclear magnetic resonance spectroscopy Methods based on optical activity and those that involve formation of complexes in cuprammonia, and dipole moments are also discussed Several theoretical studies on the conformations of the aldopyranoses are also reported By calculating the extent of atomic (Van der Waals) overlap of non-bonded atoms, the relative stabilities of the chair conformations of the aldopyranoses are estimated The chapter also describes methods for conformations of acyclic sugars and their derivatives, pyranoid sugar derivatives, and furanoid sugar derivatives, in their crystalline state and in solution The chapter also discusses anomeric effect and empirical approaches to predict favorable conformation

Conformational Analysis of Sugars and Their Derivatives

Twenty-five sugars have been compared as inhibitors of l-sorbose or d-xylose transport by the constitutive, monosaccharide transport system in bakers' yeast. d-Glucose showed the highest activity (i.e., apparent K(i) = 5 mm). Since all sugars except 2-deoxyglucose showed a decrease in activity relative to glucose (i.e., apparent K(i) = 25 - >2,000 mm), an attempt was made to relate the activity of each sugar with the way its structure differs from that of d-glucose. Assuming that the inhibition was the result of sugar-carrier complex formation, the analysis showed that the transport system has a rather broad specificity for pyranoses. Single changes at each of the five carbons of d-glucose (except for the 2-deoxy derivative) result in variable decreases in activity depending upon the carbon number and the alteration. The largest decrease in activity effected by a single change is the methylation or glucosylation of the anomeric hydroxyl. The combination of two or more changes leads to a decrease which is greater than the decrease in activity resulting from the individual changes occurring alone.

Relationship between sugar structure and competition for the sugar transport system in Bakers' yeast.

An additive all-atom empirical force field for aldopentofuranoses, methyl-aldopentofuranosides (Me-aldopentofuranosides), and fructofuranose carbohydrates, compatible with existing CHARMM carbohydrate parameters, is presented. Building on existing parameters transferred from cyclic ethers and hexopyranoses, parameters were further developed using target data for complete furanose carbohydrates as well as O-methyl tetrahydrofuran. The bond and angle equilibrium parameters were adjusted to reproduce target geometries from a survey of furanose crystal structures, and dihedral parameters were fit to over 1700 quantum mechanical (QM) MP2/cc-pVTZ//MP2/6-31G(d) conformational energies. The conformational energies were for a variety of complete furanose monosaccharides and included two-dimensional ring pucker energy surfaces. Bonded parameter optimization led to the correct description of the ring pucker for a large set of furanose compounds, while furanose−water interaction energies and distances reproduced QM H...

/pdf/charmm-additive-all-atom-force-field-for-aldopentofuranoses-1o5j8v6v22.pdf

CHARMM additive all-atom force field for aldopentofuranoses, methyl-aldopentofuranosides, and fructofuranose.

Publisher Summary This chapter explains that many developments have taken place in the applications of gas–liquid chromatography to carbohydrates. The chapter discusses a classical paper on the application of trimethylsilyl derivatives of carbohydrates in gas–liquid chromatography. The discovery that these derivatives are readily formed and that they are volatile revolutionized the separation and analysis of carbohydrate mixtures. The chapter reviews the determination of carbohydrates in biological materials by gas–liquid chromatography and the use of this method in the analysis of plant materials. In examining the structure of a polysaccharide, it is convenient to consider the methods involved under the three main headings: (1) quantitative analysis, ( 2 ) methylation, and (3) periodate oxidation. Each of these aspects of polysaccharide chemistry may be aided by the application of gas–liquid chromatography, either qualitative or quantitative, or both. Thus, separations impossible by other techniques may often be achieved, and analytical data obtained in a fraction of the time demanded by other methods.

Applications of Gas-Liquid Chromatography to Carbohydrates :Part I°

Sugars possessing the arabino (2,3,4-trans,cis) configuration exist as furanoses to a greater extent in dimethyl sulfoxide than in water. Their 2,3-di-O-methyl derivatives show an even stronger pre...

W. Mackie

Papers

Pyranose–furanose and anomeric equilibria: influence of solvent and of partial methylation