Exploitation of Primitive Molecular Recognition Effects in Electron Transfer Reactions

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Professor Hupp of Northwestern University will investigate the effects of molecular recognition on electron transfer rates with support from the Inorganic, Bioinorganic, and Organometallic Program. He plans to probe two fundamental aspects of electron transfer reactions, one being the molecular aspects of the solvation barrier, the other being the influence of the intervening medium on the donor/acceptor electronic coupling strength. He will conduct four classes of experiments to assess these issues. 1) Crown ethers in solution will bind to D/A complexes, and this binding will simulate the molecular aspects of solvation. 2) Donors and acceptors will be trapped inside hemicarcerands, and the influence on bimolecular electron transfer will likewise simulate the molecular aspects of solvation. 3) D/A complexes where the bridging ligand is a crown ether or related moiety will be examined vis-a-vis their binding of cations; this will give information on the effects on coupling strength. 4) D/A complexes will be examined as a function of the conformation of the bridging ligand;this will give information about gated electron transfer and it will help in the interpretation of the studies in part 3. The general outcome of these studies will be an enhanced understanding of how electron transfer over long distances is affected by the intervening and surrounding media. %%% One of the major types of chemical reaction is electron transfer from one atom to another. This can even occur over long distances, when the two atoms are separated because they reside in bulky molecules, or because they reside in remote sites within the same molecule. Under such circumstances the rates of electron transfer are quite sensitive to the intervening medium and also to the surrounding solvent. Experiments to gain a general understanding of these effects will be undertaken by examining electron transfer in molecules that have been designed specifically for this purpose. In particular, aspects of "molecular recognition" will be investigated. Molecular recognition means that the specific structural features of one molecule will cause it to bind to another molecule in a highly controlled way; this binding will then lead to effects on the rates that can be directly attributed to known aspects of the bound molecule.