Intramolecular hydrogen bonding, helical

Figure 8.4 Cis,cis-bilirubin, showing intramolecular hydrogen bonds which produce a helical structure that is insoluble in water...

Huang B, Parquette JR. Effect of an internal anthranilamide turn unit on the structure and conformational stability of helically biased intramolecularly hydrogen-bonded dendrons. J Am Chem Soc 2001 123 2689-2690. 

Preston AJ, Fraenkel G, Chow A, Gallucci JC, Parquette JR. Dynamic helical chirahty of an intramolecularly hydrogen-bonded bisoxazoline. J Org Chem 2003 68 22-26. 

A single a-helical molecule is stabilized by the intramolecular hydrogen bonding between the ( ) and ( + 4) residue along the peptide backbone, allowing for the formation of a right-handed helix with 3.6 amino acids per mm. However, a lone helix is rare. Typically, the helix must be stabilized by interactions with other portions of the protein or, in the case of coiled coils, it may be stabilized by interactions with additional helices. 

The X-ray diffraction patterns obtained from potassium hyaluronate films prepared from solutions of pH 3.0-4.0 were representative of the patterns from Rb+, Cs+, and NH4 forms. At 90-98% r.h., the unit cell is tetragonal, with a = b = 1.714 nm, and c = 3.28 nm. Each chain is a 4(— 0.82) helix, and two such chains fonn an antiparallel-stranded double-helix. There are two double helices in the unit cell, and the space group is 14,22. There are no intramolecular hydrogen-bonds. 

Proteins occur as helices (alpha structures) and pleated sheets (beta structures). The alpha structures are dependent on intramolecular hydrogen bonds, whereas the beta structures are dependent on intermolecular hydrogen bonding. 

The a-keratins are composed of right-handed helical polypeptide chains in which all the peptide NH and carbonyl groups form intramolecular hydrogen bonds. When these helical coils interact, they form left-handed coiled coils. 

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