Monosaccharides chemical properties

Carbohydrates Chiral Molecules Fischer Projections of Monosaccharides Haworth Structures of Monosaccharides Chemical Properties of Monosaccharides Disaccharides Polysaccharides... 

Structural elucidation of natural macromolecules is an important step in understanding the relationships between the chemical properties of a biomolecule and its biological function. The techniques used in organic structure determination (NMR, IR, UV, and MS) are quite useful when applied to biomolecules, but the unique nature of natural molecules also requires the application of specialized chemical techniques. Proteins, polysaccharides, and nucleic acids are polymeric materials, each composed of hundreds or sometimes thousands of monomeric units (amino acids, monosaccharides, and nucleotides, respectively). But there is only a limited number of these types of units from which the biomolecules are synthesized. For example, only 20 different amino acids are found in proteins but these different amino acids may appear several times in the same protein molecule. Therefore, the structure of... 

The chemical properties of monosaccharides are further complicated by the fact that they can exhibit tautomerism in aqueous basic solutions (Figure 1.15). This means that after a short time a basic aqueous solution of a monosaccharide will also contain a mixture of monosaccharides that will exhibit their characteristic chemical properties. For example, a solution of fructose will produce a silver mirror when treated with an ammoniacal solution of silver nitrate (Tol-len s reagent). This is because under basic conditions fructose undergoes tautomerism to glucose, whose structure contains an aldehyde group, which reduces Tollen s reagent to metallic silver. 

This chapter is exclusively devoted to the occurrence, significance, and physical and randomly selected chemical properties of various groups of sugars and their implications in synthetic applications of these specified classes of monosaccharides. 

The physical properties and many chemical properties of monosaccharides depend on the molecular shape. Equilibria of pyranoid compounds depend largely upon the axial-equatorial relationship between substituents on the rings. Thus, the alp ratio of pyranoses is governed to some extent by the tendency of the anomeric hydroxyl group to occupy the less hindered equatorial substituent orientation. 

Sucrose consists of two monosaccharides, glucose and fructose, joined by a glycosidic bond between carbon atom 1 of the glucose unit and carbon atom 2 of the fructose unit (O Fig. 3). Since it contains no free anomeric carbon atom (O Fig. i), it is a non-reducing sugar. Some basic chemical, physical, and physico-chemical properties of pure sucrose are listed in O Table 3. 

During the past ten years, the l,6-anhydro-/3-D-hexopyranoses have found wide application in the synthesis of hexoses and their derivatives, and of oligosaccharides, and for polymerization to polysaccharides. They can be used as model compounds in studying the physical and chemical properties of monosaccharides, as has been shown, for example, by nuclear magnetic resonance (n.m.r.) studies, and also by studies of (a) their chiroptical properties, (b) the partial reactivity of hydroxyl groups, and (c) their ability to form complexes. 

Searches for physical and chemical properties as well as links to useful biochemical and structural sites for these biomolecules can be made at ChemFinder (http //chemfinder.com). The three-dimensional models of biochemical compounds, including nucleotides, a-amino acids, monosaccharides and their derivatives, can be viewed at Klotho (http //www.biocheminfo.org/klotho/). (Figure 2.2)... 

KDO has chemical properties similar to those of neuraminic acid as it has a carboxylate group, a 3-deoxy group, and a similar biosynthesis (see Chapter 10). The monosaccharide composition, sequence, and linkages, along with the position of attachment of phosphate and ethanolamine pyrophosphate substituted onto the heptose residues of the core polysaccharide have been determined [53-58] and are shown in Fig. 9.16C. The fatty acids in the lipopolysaccharide participate in the formation of a lipid bilayer for the outer membrane. The carbohydrate is hydrophilic and is located on the outer faces of the lipid bilayer membrane. The O-antigen polysaccharides and other capsular polysaccharides are attached to position-4 of the next to last monosaccharide residue, a-D-glucopyranose of the core polysaccharide. 

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