Ribbon-type structures

The syntheses of the first sulfonio-bridged, p-phenylene ladder oligomers (44) that have a planar ribbon-type structure have also been reported (60). 

In the past five years, extensive research efforts have focused on the synthesis of ribbon-type structures consisting of an alternating series of fused six- and five-... 

Percec and coworkers [184] utilized a similar strategy for the conversion of perfluorinated alkylene functionalized 3,4,5-trihydroxy benzoic acid-type dendrons into methyl methacrylate functionalized dendritic macromonomers. Characterization of the resulting linear-dendritic architectural copolymers involved DSC, x-ray diffraction, and thermal optical polarized microscopy. It was concluded that the self-assembly of the pendant dendritic mesogens forced the linear backbone into a tilted, helical ribbon-type structure. The self-assembly behavior was largely controlled by the multiplicity, composition, and molecular weights of the pendant dendritic mesogens. 

Figure 20 Ribbon representationsof structures of the type IV collagen NCI trimer (PDB accession number 1M3D) (a) down the pseudo-three-fold axis and hexamer (b) down the two-fold NCS axis. The figure was generated using the UCSF Chimera package.

Figure 4.11. Graphic representations of protein 3D structure. Three-dimensional graphics of hen s egg-white lysozyme as visualized with RasMol (first and second rows, ILYZ.pdb) and Cn3D (third row, ILYZ.val) are shown from left to right (color type) in wireframe (atom), spacefill (atom), dots (residue), backbone (residue), ribbons (secondary structure), strands (secondary structure), secondary structure (secondary structure), ball-and-stick (residue), and tubular (domain) representations.

S. Abele, P. Seiler, D. Seebach, Synthesis, Crystal Structures, and Modelling of P-Oligopeptides Consisting of l-(Aminomethyl)cyclopropanecarboxylic Acid Ribbon-Type Arrangement of Eight-Membered H-Bonded Rings , Helv. Chim. Acta 1999, 82, 1559 - 1571. 

Many types of amphiphile can form these supramolecular structures (see Fig. 4.52). Most of these have the abiUty to form hydrogen bonds - hydrogen bond formation significantly increases the stabihty of a supramolecular assembly. The presence of a chiral center sometimes leads to the formation of ribbon-Uke structure and twisted fibers. 

The following example describes the first successful synthesis of a soluble and structurally defined ladder polymer by the stepwise route. It illustrates the synthetic potential of the classical route to ribbon-type macromolecules. 

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