Cellulose intrachain hydrogen bonds

FIGURE 7.27 The structure of cellulose, showing the hydrogen bonds (blue) between the sheets, which strengthen the structure. Intrachain hydrogen bonds are in red and interchain hydrogen bonds are in green. 

Cellulose II, derived by mercerization of cotton, crystallizes in a monoclinic unit-cell, with a = 0.802 nm, b = 0.899 nm, c = 1.036 nm, and y = 116.6°. The space group is P2,. Two chains, each with a 2(0.518) confonnation, are packed in the unit-cell, with antiparallel polarity. In addition to the OH-3—0-5 (0.269 nm), intrachain hydrogen-bond, an OH-2 —0-6 (0.272 nm), intrachain hydrogen-bond is possible only for the center down chain. This is due to the g+ orientation of the C-6-0-6 bonds in the corner chains and t orientation in... 

The cellulose II structure is more complex to unravel, since it involves two symmetry-independent chains. Polymer chain structures have been proposed that involve six different intrachain hydrogen-bond arrangements [344] ... 

Cellulose is the major wall constituent in the supporting tissues of mature plant cells. The paracrystalline structure of cellulose, that results from energy minimization by the formation of inter- and intrachain hydrogen bonds, makes it mechanically the strongest known organic molecule on density basis (Niklas 1992). It is natural then that cellulose is the primary determinant of strength in structural tissues. 

Fig. 1 Schematics of a single cellulose chain repeat unit, showing the directionality of the 1-4 linkage and intrachain hydrogen bonding dotted line) (Moon et al. 2011)...

No critical discussion of biosynthesis can be attempted without consideration of the information available on the structure of native cellulose. As for studies on biosynthesis, much controversy has existed in the field of structural analyses of cellulose. There seem to be only two points on which all workers are in agreement, namely, that (a) native cellulose is a composite of linearly extended chains of (l->4)-j6-D-glu-can (1), and (b) strong intrachain and interchain hydrogen-bonding between D-glucosyl residues occurs in such a way as to create a highly insoluble, and partially crystalline, fibrillar structure. 

The orderly and repetitive arrangement of hydrogen bonds in polymers determines their shape. The extended structures of cellulose and of peptides in a j8-sheet allow for the formation of strong fibers through intrachain H bonding. 

Figure 4 shows the chain conformations of cellulose I ("bent") and of cellulose II ("bent and twisted") proposed in our previous work (28) on the crystal structure of cellulose II. These models of cellulose I and II have one and two kinds of Intrachain (03 -05) hydrogen bond, respectively. The number of 0-H stretching peaks in... 

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