Supramolecular helix structure

Fig. 2.8. Scaffold formation/disruption assays based on supramolecular self-assemblies. In this scheme, a cyanine is helicogenic. Molecular self-assembly of cyanine upon linear chiral polymer such as CMA, CMC, or HA results in a conformation transition of the polymer to adopt a super-helix structure. Scaffold disrupting glycosidases (hyaluronidase, amylase, cellulase) trigger fluorescence attenuation by disruption of the helical scaffold...

DNA, with its special double helix structure, is a typical supramolecular system, and it plays the central role in the transcription, expression, and conservation of genetic information [62]. The biological function of DNA is closely related to the stability and the integrality of the double strands [63], and the mechanical stability of double-stranded DNA (dsDNA) strongly depends on the ambient conditions. Recently, Cui et al. investigated the important role of water in determining or stabilizing the supramolecular structure of DNA by SMFS [31, 32]. 

First described in the literature in 1814, the blue reaction of iodine with starch is the best-known example of a polymerization process induced by supramolecular stabilization. Structural studies indicate that amylose (the linear fraction of starch) forms a helix with six glucose residues per turn to include guest iodine molecules. Inside this helix, iodine molecules form a polymeric chain with a periodicity of 3.1 A, which is much shorter than the nonbonded distance between iodine atoms (4.3 A) but greater than the single I-I bond distance (2.7 A). The amylose-iodine reaction is widely used in analytical chemistry and was utilized for the solubilization and purification of carbon nanotubes. 

The x(r) graphs for the p relaxations (Figure 5.10a) demonstrate that there is deviation from the linear Arrhenius dependence Im=a/T+b because of certain cooperative motions characteristic for starch having the double-helix structure and more complex supramolecular structmes affected by water and silica nanoparticles. 

Non-covalent interactions play a leading role in controlling the secondary and tertiary structures of natural macromolecules such as peptides, polynucleotides and polysaccarides or, for example, to provide the double helix structure of DNA where the base pairing between guanine and cytosine takes place by means of a threefold H-bonding. However, it is only relatively recently that such interactions have been exploited in the molecular self-assembly of well-defined S5mthetic supramolecular structures and materials. 

We have tried to explore the gel structure at several microscopic scales the left handed helix conformation, the supramolecular structure, showing the kind of helix association (triple helices, fibers, aggregates,. ..), the role of the solvent. 

Supramolecular structure. The observation of the supramolecular structure is of a primary importance both for elucidating the mechanisms of helix growth and defining the parameters of the network. 

Mesophase with a helicoidal supramolecular structure of blocks of molecules with a local smectic C structure. The layer normal to the blocks rotates on a cone to create a helix-like director in the smectic C. The blocks are separated by plane boundaries perpendicular to the helical axis. At the boundary, the smectic order disappears but the nematic order is maintained. In the blocks the director rotates from one boundary to the other to allow the rotation of the blocks without any discontinuity in the thermomolecular orientation. 

Scheme 21 Coupling of Peptide Segments to a Bipyridyl Ligand and Fe2+ Induced Self-Assembly of a Three-Helix Supramolecular Structure 56-57 ...

The double-helical structure of DNA and the ability of the molecule to unravel in order to template the formation of copies of itself and transcribe RNA is clearly connected intimately with the supramolecular interactions that bind the two nucleotide strands together. It is the information encoded within the individual nucleobases that tells the molecule to form a double helix. This is an... 

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