Interchain hydrogen bond

The copolymers are insoluble in water unless they are neutralized to some extent with base. They are soluble, however, in various ratios of alcohol and water, suggesting appHcations where deUvery from hydroalcohoHc solutions (149) but subsequent insolubiUty in water is desired, such as in low volatile organic compound (VOC) hair-fixative formulations or tablet coatings. Unneutralized, their Ts are higher than expected, indicating interchain hydrogen bonding (150). 

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. 

The DNA isolated from different cells and viruses characteristically consists of two polynucleotide strands wound together to form a long, slender, helical molecule, the DNA double helix. The strands run in opposite directions that is, they are antiparallel and are held together in the double helical structure through interchain hydrogen bonds (Eigure 11.19). These H bonds pair the bases of nucleotides in one chain to complementary bases in the other, a phenomenon called base pairing. 

Fig. 5.—Parallel packing arrangement of the 2-fold helices of chitin I (3). (a) Stereo view of two unit cells approximately normal to the hc-plane. The two comer chains (open bonds), separated by b, in the back are hydrogen bonded to the comer chains (tilled bonds) in the front, (b) Projection of the unit cell along the c-axis with a down and b across the page. The diagonal orientation of the sugar rings facilitates interchain hydrogen bonds involving the JV-acetyl moieties along the a-axis.

Fig. 21.—Structure of the 6-fold anhydrous curdlan III (19) helix, (a) Stereo view of a full turn of the parallel triple helix. The three strands are distinguished by thin bonds, open bonds, and filled bonds, respectively. In addition to intrachain hydrogen bonds, the triplex shows a triad of 2-OH - 0-2 interchain hydrogen bonds around the helix axis (vertical line) at intervals of 2.94 A. (b) A c-axis projection of the unit cell contents illustrates how the 6-0H - 0-4 hydrogen bonds between triple helices stabilize the crystalline lattice.

Fig. 24.—(a) Stereo view of slightly over a turn of the 3-fold double helix of i-carrageenan (23). The two chains are distinguished by open and filled bonds for clarity. The vertical line is the helix axis. Six interchain hydrogen bonds per turn among the galactose residues stabilize the double helix. The sulfate groups lined up near the periphery are crucial for intermolecular interactions. 

Collagen triple helices are stabilized by hydrogen bonds between residues in dijferent polypeptide chains. The hydroxyl groups of hydroxyprolyl residues also participate in interchain hydrogen bonding. Additional stability is provided by covalent cross-links formed between modified lysyl residues both within and between polypeptide chains. 

In cellulose II with a chain modulus of 88 GPa the likely shear planes are the 110 and 020 lattice planes, both with a spacing of dc=0.41 nm [26]. The periodic spacing of the force centres in the shear direction along the chain axis is the distance between the interchain hydrogen bonds p=c/2=0.51 nm (c chain axis). There are four monomers in the unit cell with a volume Vcen=68-10-30 m3. The activation energy for creep of rayon yarns has been determined by Halsey et al. [37]. They found at a relative humidity (RH) of 57% that Wa=86.6 kj mole-1, at an RH of 4% Wa =97.5 kj mole 1 and at an RH of <0.5% Wa= 102.5 kj mole-1. Extrapolation to an RH of 65% gives Wa=86 kj mole-1 (the molar volume of cellulose taken by Halsey in his model for creep is equal to the volume of the unit cell instead of one fourth thereof). 

Mitraki and colleagues also overview the other distinctive family of /3-fibrous folds, called the triple /3-spirals (Fig. 3D). The /3-spiral folds are more complicated than the solenoidal fold, with long central /3-strands that hold the trimer together through interchain hydrogen bonds, and... 

Figure 16 Interchain hydrogen bond network in collagen triple helix. The figure was generated using the UCSF Chimera package and coordinates from PDB structure 1QSU.

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