Supramolecular rods

Hydrogen bonded dimers of 4-RF-substituted benzoic acids [119, 120, 122, 126], /rcyclohexane carboxylic acids [120], and hydrogen bonded complexes of benzoic acids with 4,4 -bipyridine and stilbazole [166, 243-246] can be regarded as supramolecular rod-like mesogens with two fluorinated chains. Figures 33 and 34 show comparisons of selected benzoic acid dimers and their bipyridine and stilbazole complexes. Comparison of the benzoic acid dimers 122 and 123 with -alkyl chains and F-terminated -alkyl chains, respectively, indicates that a single F-atom at the end of the alkyl chain reduces the mesophase stability... 

Fig. 34 Examples of supramolecular rod-like mesogens formed by self assembly of branched fluorinated benzoic acid into dimers and their 4,4 -bipyridine complexes (77° C) [166]...

Utilization of the single hydrogen bond between pyridine and benzoic acids in SLCP s has been a source of inspiration for other groups in the development of main-chain supramolecular polymers based on diacids and dipyridines.53-56 Supramolecular rod-coil polymers have been developed by assembly of 4,4 -bipyridines and telechelic polypropylene oxide with benzoic acid end-groups, which show highly ordered liquid crystalline phases.57 The use of tartaric acid derivatives in combination with bipyridine units resulted in the formation of hydrogen-bonded, chiral main-chain LCP s, as has been shown by circular dichroism measurements, optical microscopy, and X-ray data.58,59... 

Choi and Park226 have modified surfaces with cyclodextrins to assist in the electroformation of PAn nanowires. Others have utilized the concept of molecular templates to form PAn supramolecular rods with electrical conductivity improved by two orders of magnitude.227... 

The lowering of the viscosity is associated with the formation of supramole-cular rod-like structures created by aggregation of the solubilized protein chains. Figure 12.9 shows a simple model of isotropic fibroin coils, dissolved in water and arranged into orientationally ordered supramolecular rods. 

Figure 9.18 Schematic representation of the formation of supramolecular rod-coil polymer, leading to the generation of micelles. (Reproduced with permission from Reference [90]. Copyright Wiley-VCH Verlag GmbH.)...

On the other hand, it has also become clear that a materials-oriented synthesis of conjugated poly(phenylene)s cannot narrow its attention to properties of molecules only in solution, but has to include aspects of processing and supramolecu-lar ordering as well. The rigid-rod character of PPPs therefore suggests the use of chain stiffness as a structure-forming principle in the design of supramolecular motifs. 

Another key point is selective chemical functionalization at one or both ends, or inside the chain (see scheme 2).m Thus, thiolo functions can serve as clips to create contact with metal surfaces or particles. Quantitative end functionalization of the rigid-rod on one end is a key step toward rod-coil copolymer synthesis (see scheme 3),131 and such a covalent coupling of incompatible polymer blocks is relevant for supramolecular organization.141... 

Inoue et al. (2003) found that silk proteins will form rodlike structures and that those structure will assemble into comblike or fabric-like superstructure. The scale differences between the rods (nanometers) and the superstructure (micrometers) would suggest that the rod formation is governed by amyloid fibril formation and that the supramolecular arrangement is governed by the properties of the rod (Oroudjev et al., 2002 Putthanarat et al., 2000), namely surface interaction and hydration. Three levels of association could be considered (i) within the proteins internal /1-strands will organize to form intra /1-sheet structures, (ii) /1-sheets from neighboring molecules will associate to form fibril subunits, and (iii) the fibril subunits will further associate to form larger fibrils or rods. 

Controlling the size, shape and ordering of synthetic organic materials at the macromolecular and supramolecular levels is an important objective in chemistry. Such control may be used to improve specific advanced material properties. Initial efforts to control dendrimer shapes involved the use of appropriately shaped core templates upon which to amplify dendritic shells to produce either dendrimer spheroids or cylinders (rods). The first examples of covalent dendrimer rods were reported by Tomalia et al. [43] and Schluter et al. [44], These examples involved the reiterative growth of dendritic shells around a preformed linear polymeric backbone or the polymerization of a dendronized monomer to produce cylinders possessing substantial aspect ratios (i.e. 15-100) as observed by TEM and AFM. These architectural copolymers consisting of linear random... 

The rod and cone cells found in the retina of the eye are functional supramolecular devices involved in information processing. Rod cells function in dim light and are black and white receptors while cones are colour receptors. 

Kotera M, Lehn JM, Vigneron JP. Design and synthesis of complementary components for the formation of self-assembled supramolecular rigid rods. Tetrahedron 1995 51 1953-1972. 

Morphologically diverse supramolecular assemblies have been formed from long-chain chiral aldonamides [370-378]. Typical compounds include 28 30. Formation of 200- and 300-A-diameter rods and helical rope-like structures in aqueous n-octyl- and n-dodecyl-D-gluconamide (D-28-8 and D-28-12) gpls has been recognized for some time [379]. In a subsequent work, helical double-... 

Hairy rigid rod polymers, in which flexible side chains are attached to a rigid core, present attractive properties [9.155]. A supramolecular version of such materials may be the triple helical supramolecular species described above (Figure 41), which presents the features of a hairy cylinder. Similarly, the components 176 and 177 bearing long R chains yield self-assembled, supramolecular hairy rigid rods. 

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