New Redox Tags For Bioorganometallic Chemistry and Electrode Modification

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With support from the Chemical Measurement and Imaging (CMI) Program the Chemical Structure, Dynamics and Mechanisms (CSDM) Program in the Division of Chemistry, Professor William Geiger and his group at the University of Vermont are seeking to identify new directions in the application of organometallic redox tags to medical imaging and to surface science. It takes advantage of the one-electron oxidation of strongly IR-active "piano-stool" tags bonded to molecular substrates or to conducting surfaces through their cyclopentadienyl (Cp) or cyclobutadiene (Cb) rings. Before or after tagging, one or more carbonyl ligands can be substituted by donor ligands using "redox switching" to manipulate both the chemical and physical effects of the tag, including E1/2 potential, IR frequency, lipophilicity, and topology. A key goal is to provide to the chemical and biological communities a molecularly broadened toolbox of organometallic redox tags having a dramatic IR spectroscopic signature, allowing redox and IR imaging even at the cellular level. Anodic oxidative studies will be carried out for compounds in which MCp(CO)3 (M = Mn, Re) groups are tagged to tamoxifen as a model to allow, for the first time, imaging of both the location and redox state of organometallic tags in biological systems. Covalent attachment of piano-stools to electrodes will also be carried out for the purpose of providing entry to a molecularly diverse set of strongly IR-active organometallic monolayers. Piano-stool compounds anchored via cycloadditon click attachment to carbon will be characterized using advanced surface analysis methods in collaboration with the Energy Materials Center at Cornell University. Unprecedented studies of CO-substitution rates, ion-pairing effects, and monomer/dimer equilibria in organometallic monolayers will be carried out, increasing our understanding of the reactivities of surface-bound organometallics. Success in the proposed research could lead to the basis of a new approach to cell imaging, one in which the redox state of a molecular tag can be followed as a function of time and place. The proposed innovative organometallic electro-grafting methods will broaden the molecular possibilities for chemically-modified conducting surfaces, and the ways in which they may be applied to needs in catalysis, corrosion, composite materials, sensors, and energy. Strong collaborations with ENS Paris and with Prof. Jannie Swarts and other students and faculty at the University of the Free State in South Africa will provide an aspect of international outreach to the program. Expansion of the pool of underrepresented groups will be addressed through Project SEED internships at the University of Vermont (UVM) and by inclusion of African-American or Hispanic summer research interns at UVM recruited from either Chicago State University or the University of New Mexico.