MOLECULAR ENCAPSULATION AND ELECTRON TRANSFER

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The Organic and Macromolecular Chemistry Program in the Chemistry Division at the National Science Foundation supports Professor Angel E. Kaifer at the University of Miami, who will study the relationship and interplay between molecular structures and electron transfer reactions. This proposal is aimed at elucidating fundamental questions related to electron transfer (ET) reactions and how the ET rates are affected by a host in supramolecular systems. This is a major continuing effort of previous work to better understand electron transfer reactions that occur within noncovalent encapsulated redox centers. By using a redox active guest and a suitable host, the resulting inclusion complex is a structure in which the redox center is partially or completely encapsulated by the host cavity. It may be viewed as analogous to biological host-guest macromolecular systems. These experiments will seek to understand quantitative and qualitative changes in reactivity of encapsulated molecules, such as reorganization energy rates and related thermodynamic parameters. Specific objectives are to i) investigate ferrocene and its derivatives in various cucurbit[n]uril (CBn) and cavitand hosts via noncovalent binding interactions, ii) investigate mediated electron transfer between fully encapsulated ferrocence centers and electrode surfaces, iii) continue binding property studies of CBn hosts within a range of inclusion complexes, and iv) begin new research on the use of nitroxide spin labels to probe the interior space of molecular capsules to better understand the complex factors controlling self-assembly. Since CBn hosts surpass cyclodextrins, a similar class of cyclical-shaped oligosaccharides, in binding affinity and selectivity, these studies will generate meaningful information to better understand supramolecular assembly and molecular recognition of a valuable class of molecules. Cucurbiturils are efficient host molecules in molecular recognition and may find applications as supramolecular catalysts, drug delivery vehicles, play a role in information storage devices, or other materials science applications. Professor Kaifer will continue to actively engage women and underrepresented minorities from high school to post-doctoral levels in his research program. In addition to the excellent research being carried out, Professor Kaifer emphasizes student training beyond the boundaries of the traditional disciplines of chemistry. All group members are required to develop synthetic expertise and must perform their own electrochemical and spectroscopic experiments to characterize the electron transfer reactions, host-guest binding interactions, self-assembly and/or aggregation processes in which their target compounds may engage. The PI?s group has always bestowed a friendly and nurturing atmosphere for the development and training of underrepresented minorities as researchers. Several research components of this application are specifically designed for undergraduate students, since their research work often suffers from schedule limitations that do not affect graduate students and postdoctoral associates. In terms of measurable outcomes in minority training, Professor Kaifer makes the commitment that the research participants in this project will include: (a) a minority/female undergraduate every year, (b) a minority/female high school student every year, and (b) at least a minority/female postdoctoral associate or graduate student during the grant cycle.