Glucose, crystalline structure

Historically, techniques such as the formation of osazones and the demonstration of fermentation have contributed significantly to the separation and identification of carbohydrates. Observation of the characteristic crystalline structure and melting point of the osazone derivative, prepared by reaction of the monosaccharide with phenylhydrazine, was used in identification. This method is not completely specific, however, because the reaction involves both carbon atoms 1 and 2 with the result that the three hexoses, glucose, fructose and mannose (Figure 9.19), will yield identical osazones owing to their common enediol form. 

Hemicelluloses are constituted of different hexoses and pentoses glucose, mannose, xylose, etc. Since these heteropolysaccharides are often branched polymers, they cannot constitute crystalline structures. However, their function in the constitution of natural fibres is crucial. Together with lignin, they constitute the bonding matrix of the cellulose microfibres. 

The Fischer projection formula for D-glucose (Example 2.3) is also known as the open- or straight-chain structure. This structure occurs only in solution. There are two crystalline forms of D-glucose, known as a and /3, which also have different optical activities when dissolved. X-ray diffraction studies have confirmed chemical evidence that a- and /3-D-glucose are structures containing a ring of five carbon atoms and one oxygen atom ... 

The crystalline structure of cellulose has been characterized by X-ray diffraction analysis and by methods based on the absorption of polarized infrared radiation. The unit cell of native cellulose (cellulose I) consists of four glucose residues (Figs. 3-6 and 3-7). In the chain direction (c), the repeating unit is a cellobiose residue (1.03 nm), and every glucose residue is accordingly displaced 180° with respect to its neighbors, giving cellulose a... 

Cellulose is a polymer composed of glucose units linked by J-l,4-glycosidic bonds (Fig. 1). Its linear structure is strengthened by hydrogen bonding and van der Waal s forces between chains, resulting in a crystalline structure [27],... 

Chemically, about 35-55% of the dry material is the glucose polymer cellulose, much of which is in a crystalline structure while another 25—35% is hemicellulose, an amorphous polymer. The remainder is mostly lignin plus less amounts of minerals, waxes, and other compounds [3]. Cellulose is formed by beta-[l, 4] glucosyl linkages in a linear backbone, whereas hemicelluloses are branched polymers composed of several monosaccharides [5]. Fig. 1 shows the schematic illustration of the cellulose chain, while Fig. 2 shows the schematic illustration of xylans from Gramineae [5, 6]. 

Cellulose is a homopolymer of 6-(l-4) D-glucose molecules linked in a linear chain, with alternating sub-units in the crystalline structure being rotated through 180°. Native cellulose I microfibrils are highly ordered crystals and evidence from... 

Figure 7.1 Typical chemical structure of celluloses. The structure of cellulose is composed of glucose monomers linked by (5-glycosidic bonds. Strong hydrogen bonds link glucose units between different polymer chains, leading to crystalline structures that are resistant to water.

Inverse Opal Sensors. Colloidal crystals are ordered crystalline structure obtained via the self-assembly of monodispersed colloidal particles. Dried colloidal crystals can be used to template the polymerization of infiltrated monomer precursors. After polymerization, the colloidal template is removed by chemical etching, yielding a bicontinuous polymer/solvent mesostructure, i.e., inverse opal. Because of its periodically ordered structure inherited from the colloidal crystal template, inverse opal also shows structural color as a result of light diffraction. This property has also been used to design optical glucose sensors (Scheme 10.5f). 

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