Intertwined helices

Figure S.21 The hemaggiutinin moiecuie is formed from three subunits. Each of these subunits Is anchored In the membrane of the influenza vims. The globular heads contain the receptor sites that bind to sialic acid residues on the surface of eukaryotic cells. A major part of the subunit interface is formed by the three long intertwining helices, one from each subunit. (Adapted from I. Wilson et al.. Nature 289 366-373, 1981.)...

Figure 7.55 (a) The framework of )LU-10 viewed along the [ 100] direction. The [Co( dien) 213+ ions reside in the 12-membered-ring channels, (b) A space-filling diagram of two intertwined helices that enclose the 12-MR channel. Reproduced with permission from [110]. Copyright (2003) Wiley-VCH... 

F-F through-space couplings have been applied by Schwarz et who performed studies on the structural properties of perfluorinated linear alkanes. They proposed a molecular model in which delocalized p-electrons of the fluorines cover the entire surface of the molecule in two pairs of intertwined helices. 

Hirsch. K.A. Wilson. S.R. Moore, J.S. Crystallization of 3-cyanophenyl 4-cyanobenzoate with AgSbF6 A polar coordination network based on the crisscrossing of intertwined helices. Chem. Commun. 1998. 13-14. 

Stereo-complexation occurs not only in PLLA/PDLA blends, but also in PLA/ chirality systems, such as PDLA/peptides. Homo-stereo-complex of PLLA and PDLA consists of 3i-helix crystallites. Similarly, hetero-stereo-complex is composed of intertwined helices formed by PDLA blocks and peptides, which presents great interest for the sustained release of peptides. 

The melting points and heats of junction formation of curdlan gels depend on the concentration and DP of the polysaccharide [a (1 3)-P-D-glucan from Alcaligenes faecalis. The junction zones of the gels appear to form in regions of aggregation of intertwined helices. X-Ray diffraction studies have revealed that curdlan assumes a triple-helical structure. ... 

Although the field of double helical foldamers is yet to be fully explored, we believe that the creation of novel structures with unique and advanced functions such as circularly polarized luminescence and artificial transmembrane ion channels may stem from the double helical topology. As a result, the combinations of multiple chemical components present in the intertwined helices that form when two oligomers are instructed to self-assemble together provides a coherent platform on which supramolecular chemists will stand and lead an orchestra of secondary interactions. 

There have been a number of proposals of complex dye columns, including a recent study of the azo dye C. I. acid red 266, where the X-ray diffraction evidence strongly indicates columns with a cross sectional area six times larger than an individual molecule [53, 54]. Furthermore, there is a sharp 0.37 nm axial reflection. This is sufficiently far removed from the aromatic ring thickness of 0.34 nm to rule out a simple untilted columnar structure. A hollow chimney made up from a number of intertwined helical stacks appears to be the most likely structural unit (Fig. 11). Note that since the molecules in this case are non-chiral, a racemic mixture of right- and left-handed columns is probable. 

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