Thermal and Photochemical Reactions of Transition Metal Complexes of the Nitrogen Oxides and other Small Molecules

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This award in the Inorganic, Bioinorganic and Organometallic Chemistry program of the National Science Foundation supports continuing investigations by Prof. Peter C. Ford at the University of California, Santa Barbara into two aspects of nitrogen oxide chemistry involving transition metal complexes. In the first, Prof. Ford and his students are studying the synthesis and photochemical properties of complex compounds for which one part contains a precursor of nitric oxide (NO) that can release this NO to a target upon excitation with light. The second part of the complex is a strongly absorbing antenna, which will serve to gather light and transfer that energy to the NO precursor. Such NO donors have potential applications in mammalian biology given the importance of NO as a regulator of various biochemical functions. Moreover, the fundamental principles in elucidating the photochemical properties of such materials can be extended to the potential delivery of other small molecule bioregulators. Along these lines, the Ford group has initiated a new project investigating the preparation and fundamental photophysical behavior of nanomaterials in which the light absorbing antenna is a semiconductor quantum dot (QD) with diameter of 2-5 nm. Quantum dots have tunable optical properties, and we have now demonstrated that excitation of QDs leads to reactions from NO precursors at the surface. Ongoing studies prepare new materials and will employ state-of-the-art photophysical techniques to elucidate the mechanisms by which these antennas transfer energy to the reactive center and to probe whether the non-linear optical properties of QDs can be exploited to enhance their effectiveness as antennas. The other technical aspect of this project is concerned with the reactions of various nitrogen oxides (NOx) with metals such as iron and copper in appropriate ligand environments relevant to the mammalian biochemistry of the nitrogen oxides. Ongoing studies are using low temperature isolation and spectroscopy to elucidate the NOx--metal bonding modes and simple reactions under carefully controlled delivery of reactants and variation of temperatures. Related studies of the reactivity in solutions allow characterizing the dynamics of reactions such as oxygen atom transfer reactions from coordinated NOx species to various organic molecules. For example, there is increasing interest in the role of nitrite ion in physiology, and the present bioinorganic studies of this species are directed toward providing a better understanding of the fundamental chemical processes that are involved. The research performed under this award also serves as a template for the training of UCSB undergraduate and graduate students and for the further education of postdoctoral scholars in the nuances of creative scholarship. A continuing collaboration with Prof. Alexei Iretskii at Lake Superior State University (MI) also provides research opportunities for Dr. Iretskii and undergraduate LSSU students. Members of the Ford group have participated actively with other UCBS personnel in scientific outreach programs to local K-12 schools. Undergraduates leaving the group have entered graduate and medical school programs and the Ph.D. and postdoctoral graduates (including several underrepresented minorities) have moved on to independent industrial, government and faculty positions, enhancing the US scientific talent pool.