Cellobiose structure

Cation (Section 1 2) Positively charged ion Cellobiose (Section 25 14) A disacchande in which two glu cose units are joined by a 3(1 4) linkage Cellobiose is oh tamed by the hydrolysis of cellulose Cellulose (Section 25 15) A polysaccharide in which thou sands of glucose units are joined by 3(1 4) linkages Center of symmetry (Section 7 3) A point in the center of a structure located so that a line drawn from it to any element of the structure when extended an equal distance in the op posite direction encounters an identical element Benzene for example has a center of symmetry Cham reaction (Section 4 17) Reaction mechanism m which a sequence of individual steps repeats itself many times usu ally because a reactive intermediate consumed m one step is regenerated m a subsequent step The halogenation of alkanes is a chain reaction proceeding via free radical intermediates... 

Study of the structure of cellulose (Figure 22.2) leads one to expect that the molecules would be essentially extended and linear and capable of existing in the crystalline state. This is confirmed by X-ray data which indicate that the cell repeating unit (10.25 A) corresponds to the cellobiose repeating unit of the molecule. 

Despite the similarities of their structures, cellobiose and maltose have dramatically different biological properties. Cellobiose can t be digested by humans and can t be fermented by yeast. Maltose, however, is digested without difficulty and is fermented readily. 

Cellulose consists of several thousand o-glucose units linked by l- 4-/3-glyco-side bonds like those in cellobiose. Different cellulose molecules then interact to form a large aggregate structure held together by hydrogen bonds. 

A monoclinic unit-cell with a = 8.2 A (820 pm), b(fiber axis) = 10.30 A (1.030 nm), c — 7.90 A (790 pm), and /3 = 83.3° is used. The distance between the terminal oxygen atoms in the cellobiose unit is taken to be 10.3912 A (1.03912 nm). A left-handed, helical structure, with seven cellobiose residues in a pitch of 72.1 A (7.21 nm) was proposed. The packing arrangement involves the central reversed and comer chains, and a relative shift between them of 0.25 repeat length along the b axis. 

A different kind of host consisting of a peptide-based bicyclic structure has been described.118 In this case, the chemical shifts changes were followed by HSQC spectra in deuterated acetic acid and in water, when titrated with cellobiose. In any case, a low but measurable binding affinity constant was found. 

The torsion angles predicted by conformational analysis agree closely with those of crystalline cellobiose as measured by X-ray diffraction, the conformation of which is restricted by two chain-stabilising intramolecular hydrogen bonds between 0(3 )-H and 0(5) and also between 0(2 )-H and 0(6) (Figure 4.3). These are also found in cellulose and they assist in maintaining the highly extended conformation which allows it to function as a structural polymer. 

Figure 4.19 The structures of the disaccharides maltose and cellobiose, derived from the hydrolysis of starch and cellulose, respectively.

Figure 9.15 Structure of disaccharides. Maltose and cellobiose are both disaccharides which contain only glucose units, the difference in their structures lying in the way the glucose units are joined. The glycosidic linkage in maltose is afl—>4), whereas that in cellobiose is (1—>4).

Figure 2.3 The molecular structure of /3-D-glucopyranose (a), cellobiose (b) and the glucopyranose backbone of cellulose (c), and (d) a schematic of the linear arrangement of the glucopyranose units.

Since the primary structure of a peptide determines the global fold of any protein, the amino acid sequence of a heme protein not only provides the ligands, but also establishes the heme environmental factors such as solvent and ion accessibility and local dielectric. The prevalent secondary structure element found in heme protein architectures is the a-helix however, it should be noted that p-sheet heme proteins are also known, such as the nitrophorin from Rhodnius prolixus (71) and flavocytochrome cellobiose dehydrogenase from Phanerochaete chrys-osporium (72). However, for the purpose of this review, we focus on the structures of cytochromes 6562 (73) and c (74) shown in Fig. 2, which are four-a-helix bundle protein architectures and lend themselves as resource structures for the development of de novo designs. 

Figure 1. Conformations of cellobiose with inter-residue intramolecular hydrogen bonding. (a,b) conformations with two inter-residue bonds, (c) hydrogen bonding observed in the crystal structure (18).

Figure 2. A contour diagram of the conformational energy of p-cellobiose computed from eqn. (6) holfing constant all variables except < ), v see ref. 5 for details. The rigid glucose residue geometry was taken from ref. 23, and the valence angle p at 04 was chosen as 116 in accordance with the results of pertinent crystal structure determinations. Contours are drawn at 2,4, 6, 8,10,25, and 50 kcal/mol above the absolute minimum located near ( ), v = -20 , -30 higher energy contours are omitted.

Figure 10. Relaxed (adiabatic) conformational energy map for p-maltose as computed by Brady and coworkers.i3 Contours are drawn at 2,4,6, 8, and 10 kcal/mol above the minimum near < ), y = -60°, -40°. The p-maltose structure may be derived from that of p-cellobiose in Fig. 1 by inversion of the stereochemical configuration at Cl.

A short presentation of the Consistent Force Field is given, with emphasis on parametrization and optimization of energy function parameters. For best possible calculation of structure, potential energy functions with parameter values optimized on both structural and other properties must be used. Results from optimization with the Consistent Force Field on alkanes and ethers are applied to glucose, gentiobiose, maltose and cellobiose. Comparison is made with earlier and with parallel work. The meaning and use of conformational maps is discussed shortly. 

Figure 2. The four starting models used for the study of cellobiose (lone pairs of electrons are not shown). Convention defines the R and C notation when the residue is in a conventional orientation and is viewed from above. The least energetic structure observed in this study is gtgtRR. This Figure and Figure 5 were drawn with CHEMX, developed and distributed by Chemical Design Ltd, Oxford, England.

---