While most chemical research to this point has been devoted to the delineation and manipulation of intramolecular chemical bonding in a conventional sense, our research focuses on the chemistry beyond the molecule in a field now known as Supramolecular Chemistry. Our interests lie in characterization and manipulation of the intermolecular non-covalent interactions (i.e., hydrogen bonding, cation...p, charge-charge, hydrophobic-hydrophobic, charge transfer interactions, etc.) that are responsible for the complex molecular interplay mechanisms known to be prevalent in biological systems. Although most biologically based supramolecular systems are far too complex to be studied systematically in terms of separate interactions, a smaller synthetic system may be studied in significantly greater detail. It is in this context that our group synthesizes and examines a broad array of host-guest chemical systems (ex., liquid clathrates, macromolecular hosts) with one of our principal methods of characterization being single crystal X-ray structure determination.

A main theme of our research is associated with the link between the solid geometry principles of Plato and Archimedes and the chemical assembly of small building blocks into large supramolecular structures. Specifically, the discovery that members of the resorcin[4]arene family, 1, self-assemble to form the capsule shown below, 2, prompted my research group to examine the topologies of related spherical hosts with a view to understanding their structures on the basis of symmetry. In addition to providing a grounds for classification, it was anticipated that such an approach would allow one to identify similarities at the structural level, which, at the chemical level, may not seem obvious and may be used to design large, spherical host assemblies.

Our group has now described the results of this analysis which we regard as the development of a general strategy for the construction of spherical molecular hosts. In these reports we began by presenting the idea of self-assembly in the context of spherical hosts and then, after summarizing the Platonic and Archimedean solids, we provided examples of cubic symmetry-based hosts, from both the laboratory and nature, with structures that conform to these polyhedra.

The Platonic solids comprise a family of five convex uniform polyhedra (Table 1) which possess cubic symmetry and are made of the same regular polygons (equilateral triangle, square, pentagon) arranged in space such that the vertices, edges, and three coordinate directions of each solid are equivalent

That there is a finite number of such polyhedra is due to the fact that there exists a limited number of ways in which identical regular polygons may be adjoined to construct a convex corner. There are thus only five such isometric polyhedra, all of which are achiral.

In addition to the Platonic solids, there exists a family of 13 convex uniform polyhedra known as the Archimedean solids. Each member of this family is made up of at least two different regular polygons and may be derived from at least one Platonic solid through either truncation or twisting of faces (Table 2). In the case of the latter, two chiral members, the snub cube and the snub dodecahedron, are realized. The remaining Archimedean solids are achiral.

Our research is currently engaged in the use of the Platonic and Archimedean solids as models for supramolecular assemblies.

An important outgrowth of the work briefly described above was the discovery of a method of control of molecular architecture such that in one example a spherical assembly (a great rhombicuboctahedron, an Archimedean solid) was converted into a tubular structure. Amphiphilic polydedron-shaped p-sulfonatocalix[4]arene building blocks, 3, which have been previously shown to assemble into bilayers in an antiparallel fashion, have been assembled in a parallel alignment into spherical, 4, structures by the addition of pyridine N-oxide and lanthanide ions. Crystallographic studies revealed the manner in which metal ion coordination and substrate recognition direct the formation of these supramolecular assemblies. The addition of greater amounts of pyridine N-oxide changed the curvature of the the assembling surface and resulted in the formation of extended tubules.

The amount of 'chemical space' enclosed by 4 is about 1,000 ų. This space houses 30 water molecules and two sodium ions. However, the van der Waals volume of 3 is about 11,000 ų. 4 is differentiated from 2 by several factors. First, the supramolecular forces used to hold 2 together are hydrogen bonds, while a combination of van der Waals forces, p-stacking forces, and metal ion coordinate covalent bonds is employed for 4. Second, the surface which encloses the chemical space is essentially one atom thick for 2, while it is the thickness of the p-sulfonatocalix[4]arene building block in 4 (hence, the 11,000 ų volume of the assembly with only 1,000 ų of space within). Third, the contents of the capsule are rather completely ordered for 4 (by the hydrogen bonds from the enclosed water to the phenolic oxygen atom hydrogen bond acceptors at the base of the p-sulfonatocalix[4]arene), but the contents are completely disordered for 2 (because of the lack of any directional bonding force connecting the skeleton of the assembly to the contents therein).

We have very recently made significant breakthroughs in the enclosure of chemical space, as the figures below indicate. Visit this website again for the new information as it becomes available.

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