A central theme of the research in our laboratory is the development of new methods and instrumentation in magnetic resonance spectroscopy targeted toward the elucidation of molecular structure and chemical dynamics in complex materials containing both electron and nuclear spins. Two broad areas of application dominate our research: the characterization of novel optical materials; and structural biology of proteins with metal and free radical centers - with a particular emphasis on the biochemistry of NO.
In the first application, we use magnetic resonance techniques to analyze the composition of new solid-state laser materials - primarily materials under development by local optics industry. Our approximate goal is to determine the identity, oxidation state, and incorporation sites of transition metal ion guests and defects in the materials. Our results provide a basis for refining synthesis techniques and for developing leads for new types of laser materials. On a fundamental level, we are studying the electron-transfer chemistry that occurs among redox active metal ions in insulators, with the goal of exploiting this chemistry to develop new materials with photon-modulated optical properties.
In pursuit of these goals, we have recently installed a novel, 95 GHz electron paramagnetic resonance (EPR) spectrometer, It is the only high-frequency EPR instrument in the west, and is arguably the most advanced and versatile of all instruments currently in operation in the United States. A key feature of this instrument is its capabilty for characterizing inherently small samples, such as optical fibers.
The second area embraces our long-term goal of establishing methods for the site-selective structural characterization of large, biological molecules. This work has featured studies of the catalytic active site in the G-protein, ras p21, by means electron-spin echo envelope modulation (ESEEM), and high-frequency EPR spectroscopy. Recently, we have initiated site-directed spin labeling (SDSL) of the ligand binding site in the formyl-peptide G-protein coupled receptor of human neutrophils. In our high-frequency EPR instrument, spin-label EPR experiments are feasible with as little as 10 picomoles of sample - a hundred-fold reduction as compared to conventional instruments.
A major thrust of our biophysical research involves the biological activity of NO. The production of nitric oxide is linked to a diverse set of biological activities, which span vascular, pulmonary, neural, and immunological domains, and intriguingly embrace both toxic and salutary effects. Our research in this area is focussed on the interplay between metal-centers and thiol effectors in evoking the biological activity of NO.
It has recently been discovered that human hemoglobin undergoes nitrosylation in vivo at both heme-iron and thiol (Cys93 in the ÃŸ-subunits) groups. Moreover, there appears to be a mutual allosteric modulation of dioxygen binding to the heme, and NO-group displacement from heme to thiol. This chemistry is conjectured to play a key role in regulation blood pressure and flow. Our group is using EPR spectroscopy in combination with other spectroscopic techniques - including UV/VIS, IR, and resonance Raman - to test and refine emerging models of the chemical dynamics of NO-hemoglobin interactions.