Molecular cylinders

Table 1. Dimensions of Cone-Shaped Molecular Cylinders of Cyclodextrins...

Fig. 7. a Cross sectional profile of an ultrathin film of dendrimer 23 on HOPG along x-x as indicated in (b). The height difference between adjacent terraces has the dimension of a monolayer [Ah = 4.3 ( 0.2) nm]. Large scale (2.4 x2.4 pm2) SFM image of monomolecular terraces, c Schematic model of closely packed molecular cylinders in thin films of 23 on HOPG... 

Brushes with long side chains can be synthesized by polymerization of macromonomers [117-119] or by grafting of the side chains to [16-20] or from [21] a main chain. In contrast to globular dendrimers, these molecules have an anisotropic primary structure and experience bending or coiling of the molecular contour. Depending on the relative stiffness of the main and side chains, one may distinguish four types of molecular cylinders (Fig. 20). 

M and M are alternatively characterized by the radius of gyration (J ), which is visualized as the radius of a thin circle transversely excised from an imaginary molecular cylinder, having a proximal end fixed at the center and a distal end traveling randomly along the circumference. The mass density is highest at the proximal end (Tanford, 1961). Random-walk theory indicates that the distal end will eventually maintain an equilibrium distance in the vicinity of the proximal end. 

Bonar-Law and Saunders have demonstrated that cyclocholates (see 27 Figure 3.5) reversibly self-assemble in organic solvents to form short, molecular cylinders... 

Figure 3.5 Reversible self-assembly of a short molecular cylinder through dimerisation of the cyclic chloric derivative 27 ...

Apart from the parent CDs, fully synthetic CD analogs may have some advantages in the construction of mechanically-interlocked systems. Thus, o/L-altemating cyclic oligosaccharides designed and synthesized in our laboratories have Sn symmetry and so behave as molecular cylinders rather than as molecular lampshades. 

Carbon nanotubes (CNT) consist of molecular cylinders of pure, hexag-onally-arranged carbon atoms with a diameter of a few nanometres and a length of many microns. They occur in two main forms the single-wall carbon nanotube (SWNT) composed of a single lattice cylinder of carbon, and the multi-wall nanotube (MWNT) version, consisting of concentric lattice cylinders of carbon they resemble one cylinder within another. The ends of the tubes are usually closed off by a carbon end-cap, also in lattice form. 

Fig. 1. Design of a dendronized pol5Tner whose dendritic layer is so densely packed around the backbone that it is stretched out and a molecular cylinder with a surface is generated.

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