The Macromolecular, Supramolecular and Nanochemistry (MSN) Program of the Division of Chemistry supports the work of Professor Jerry L. Atwood in the area of nanocapsule design and synthesis. The objectives of this research include: (1) the synthesis of new capsules seamed by metal-ion coordination; (2) transport across capsule walls; (3) the synthesis of very large nanocapsules and (4) tube assemblies seamed by metal-ion coordination. The increased understanding of the self-assembly process involved in the nanocapsule assembly will have ramifications in other areas of metal-ion induced self-assembly. In addition, the development of capsules over a range of sizes will provide new containers for carrying out chemical reactions in constrained environments. The extension of the research from capsules to tubes involves a logical development of the self-assembly process which terminates with the formation of a capsule to that which extends essentially infinitely in one dimension.
In addition to providing new fundamental knowledge, this research on nanocapsules presents opportunities for practical applications such as targeted drug delivery and catalysis. Furthermore, this research contributes to the development of human resources in sciences. The undergraduate students, the graduate students, and the postdoctoral fellows involved in this program will be trained to carry the research forward with the understanding that such basic research is goal oriented.
Chemical reactions generally occur in solution. In order to understand a chemical reaction, the scientist usually needs to have picture of the chemical which is reacting. This is especially important in using pharmaceutical drugs to treat an illness. Our research has led to such pictures of biological mimics. Nanoassemblies of hydrogen-bonded and metal-seamed pyrogallol[4]arenes possess novel solution-phase geometries. It has been demonstrated that both guest encapsulation and structural rearrangements may be studied by solution-phase techniques such as small-angle neutron scattering (SANS) and diffusion NMR. Application of these techniques to pyrogallol[4]arene-based nanoassemblies has allowed differentiation among spherical, ellipsoidal, toroidal, and tubular structures in solution, determination of factors that control the preferred geometrical shape and size of the nanoassemblies; and detection of small variations in metric dimensions distinguishing similarly and differently shaped nanoassemblies in a given solution. The iron-seamed C-methylpyrogallol[4]arene nanoassembly was found to be tubular in solution and predicted to be tubular in the solid state, but was found to undergo a rearrangement from a tubular to spherical geometry in solution as a function of base concentration. The absence of metal within a tubular framework affects its stability in both solution and the solid state; however, this instability is not necessarily characteristic of hydrogen-bonded capsular entities. Even metal seaming of the capsules does not guarantee similar solid-state and solution-phase architectures.
