Arborol structures

Arborol Dendrimers. The spherical topology of dendrimers resembles the size and shape of the Hartley model (1936) of a micellar aggregate formed by surfactant molecules (Fig. 11.2 Tomalia et al. 1990). Micellar stmctuies have a dynamic, spherical structure possessing a close-packed, solvent-incompatible core surrounded by an open, solvent-compatible layer. 

Figure 11.3 Chemical structures of the (a) arborol dendrimer and (b) water-soluble, allhydrocarbon dendrimer.

Figure 11.29 (a) Structure of Newkome s two-directional arboral molecule, (b) Negatively stained transmission electron micrograph of the arborol gel. (c) Schematic representation of the formation of a long fibrous rod structure via orthogonal stacking of the arboral molecules. Reprinted from Newkome et al. (1990). Copyright 1990 American Chemical Society. 

Figure 23. Structure of a compound made by a metal-complex core and appended organic arborols/ ...

Another approach to controlled molecular morphogenesis is provided by the generation of globular molecules such as the starburst dendrimers and the arborols , based on highly branched structures formed via cascade processes and growing from a central core [7.55-7.60]. Most such molecular scaffolding hase been produced by repetitive processes the use of sequences of different reactions is expected to give access to an even richer variety of non-repetitive branched architectures. 

Numerous metallomacrocycles self-assemble from their components giving species possessing various structures, for instance triangular shape [9.30,9.31] containing a cavity [9.32], which may include a guest molecule [9.33] square [9.34,9.35] or star like [9.36-9.39] shapes wheel-shaped or toroidal hexameric [9.40], octameric [9.41] or decameric [9.42,9.43] structures square [9.44,9.45] rectangular [9.46,9.47] or bent [9.48] boxes into which substrate molecules may bind [9.49,9.50] adaman-tanoid shape [9.51,9.52] with cation inclusion [9.51c], formally related to that of the spheroidal macrotricycle 21 catenane type [9.53]. Coordination species of dendri-mer or arborol nature have been constructed [7.61, 8.27, 9.54]. 

In addition to the repeat unit sequence, another area of current interest in polymer structural control (Fig. 1) may be the spatial or three-dimensional shapes of macromolecules. In fact, the recent development of star [181-184] and graft [185] polymers, as well as starburst dendrimers [126], arborols [186,187], and related multibranched or multiarmed polymers of unique and controlled topology, has been eliciting active interest among polymer scientists. In this section, let us consider the following macromolecules of unique topology for which living cationic polymerizations offers convenient synthetic methods that differ from the stepwise syntheses (polycondensation and polyaddition) [126,186,187]. 

Newkome, G. R. Moorefield, C. N. Baker, G. R. Johnson, A. L. Behera, R. K. Angew. Chem. 1991,102,1205-1207 Angew. Chem., Int. Ed. Engl. 1991,30,1176. Arborol is a synonym introduced by G. R. Newkome and resulting from merging Arbor (Latin tree) and alcohol. It is the expression for the treelike structures and the alcohol functionalities in these cascade molecules. 

Synthetic bolaphilic membranes can be tailored to provide binding sites for guests,1317 or other functionality can be incorporated, such as redox- and/or photoactive moieties.4 The repertoire of bolaam-phiphilic assemblies include gels formed by specific two-directional arborols,3 18-20 and rods and tubules formed by a-(L-lysine)-co-aminobo-laphiles.21 Inclusion of polymerizable functionalities, in either the head groups or within the lipophilic spacer, can provide convenient routes to extended covalently linked domains.9,22 23 Bolaphiles also provide synthetic chemists with tools to explore novel molecular architectures, as well as interactions between juxtaposed structural elements. Examples cited herein illustrate recently reported work in this field. 

In order to exploit the lipophilic core of the cylindrical aggregate, V,A, V",A "-tetrakis[2-hydroxy-1,1 -bis(hydroxymethyl)ethyl]hexadec-8-yne-l,l,16,16-tetracarboxamide was prepared this unsaturated ar-borol, possesses a centrally located alkyne moiety, and upon dissolution in water forms a gel comprised of a similar stacking motif to the saturated counterpart. The electron micrograph of this gel showed a unique aggregation pattern, in which bundles of intertwined aggregate columns were formed. The resultant, inherently helical pattern is in stark contrast to the needle-like structures formed by the related [9]-10-[9]-arborol. 

Vogtle s early work on cascade molecules was followed by the synthesis of highly branched polyols in the laboratory of Newcome (Fig. 3) [62], Since the first polyol structures reminded him of small trees, they were named arboroles (lat. arbor - tree). However, it has been the Greek-derived term dendrimer (8ev5pov - tree, pspcx - particle), which has become the most popular term for highly branched monodisperse molecules with fractal character, as first used in a patent... 

An interesting series of polynuclear species of large nuclearity, which because of their shape can be called "dendrimers" or "arborols", has been obtained using Ru(II) and/or Os(II) as metal centers, 2,3-dpp and/or 2,5-dpp as bridging ligands, and bpy or 2,2 -biquinoline (biq) as terminal ligands (Fig. 2).23-34 structure of a decanuclear complex of this family is... 

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