Helical chains/molecules/structures

Fibrous proteins can serve as structural materials for the same reason that other polymers do they are long-chain molecules. By cross-linking, interleaving and intertwining the proper combination of individual long-chain molecules, bulk properties are obtained that can serve many different functions. Fibrous proteins are usually divided in three different groups dependent on the secondary structure of the individual molecules coiled-coil a helices present in keratin and myosin, the triple helix in collagen, and P sheets in amyloid fibers and silks. 

Fig. 17 Section of the helical chain structure found in (C70)(o-carborane)(CTV)(l,2-dichloro-benzene) 34 with C70 guest molecules in each CTV molecular cavity [79]... 

A second form, ft-SO3, consists of polymeric molecules in helical chains made up of SO4 tetrahedra. The third form, a-S03, has the lowest vapor pressure and the highest melting point of the three forms. In this form, chains are present, but cross-linking produces a layered structure. 

The Pb—Br bond (2.696 A) has been shortened relative to the terminal bond (2.852 A) and the bridging (3.106 A) Pb—Br bonds in the parent Lewis acid, which adopts a helical chain structure . The molecule Ph2PbCl2 forms chains in which an octahedral Pb atom is linked by Cl bridges. 

---