Boyd Goodson
Research in the Goodson group will focus on the development of novel techniques in optical/nuclear double resonance (ONDR) spectroscopy, and the application of these techniques towards the study of structure, dynamics, and interactions of molecules and proteins. We are also greatly interested in exploiting the intrinsic advantages of ONDR to perform research of a more interdisciplinary nature, including: enhancing the NMR detection sensitivity and selectivity of materials surfaces and thin films (as well as living tissues, via MR Imaging); and “polarization-enhanced” NMR quantum computation.
Overview
Generally speaking, our research will be directed toward the development and application of new spectroscopic tools for studying the structure and dynamics of matter. Optical/nuclear double resonance techniques have enormous potential for probing a wide range of systems because they combine the high detection sensitivity of optical (laser-based) spectroscopies with the well-resolved spectral sensitivity to structure, dynamics, and morphology of nuclear magnetic resonance (NMR) spectroscopy.
Indeed, NMR has been established as one of the premiere analytical tools that scientists have at their disposal, permitting—for example—the detailed study of structure and dynamics of molecules in solution—including 3-D structural determination for proteins; the characterization of bulk and surface properties of materials; and the non-invasive (MRI) imaging of living tissues to elucidate pathology and function. These capabilities exploit key NMR observables that are both microscopic (e.g., chemical shifts, scalar couplings, and spin relaxation) and macroscopic (e.g. spin position, density, and velocity) in nature. However, conventional NMR methods suffer from a common drawback that in many circumstances, can limit their power and applicability—a notorious lack of sensitivity. This fundamental insensitivity originates from the miniscule size of nuclear magnetic moments, which typically results in an exceedingly weak nuclear spin polarization. Specifically, this low detection sensitivity can translate directly into a variety of critical limitations, including the attainable spatial and temporal resolution, the available information content in structural determination, and the amounts of substances and the relative surface areas of materials that can be studied.
In order to combat this sensitivity problem, we are interested in developing a number of ONDR techniques. One such approach—known as optically pumped nuclear magnetic resonance (OPNMR) spectroscopy—exploits the well-known phenomenon of optical pumping (OP) to directly enhance the detected NMR signals. For example, by applying resonant circularly-polarized laser light, angular momentum can be transferred from laser photons to the electronic spins of an alkali metal vapor (like rubidium)—and then subsequently transferred to the nuclear spins of noble gases (like xenon) via collisions—thereby temporarily enhancing their nuclear spin polarization by 10,000 to 100,000-fold. Because the detectable magnetization in NMR is directly proportional to the spin polarization, this enhancement translates directly into an improvement in detection sensitivity of four to five orders of magnitude for such “laser-polarized” gases.
Laser-polarized gases hold great potential for novel magnetic resonance applications across many disciplines, including physical, biophysical, and analytical chemistry, materials science, and medicine. For example, the high sensitivity of xenon's NMR parameters (e.g., chemical shift and spin relaxation)---combined with xenon's negligible chemical reactivity, lipophilicity (xenon is known to bind specifically to hydrophobic and amphiphilic regions of many proteins), and the bright NMR signal endowed by optical pumping—make laser-polarized xenon a powerful (but ultimately indirect) probe of cavities and surfaces of molecules and materials. Moreover, the use of both laser-polarized xenon and helium for imaging void spaces (e.g. lung space), tissues, and blood flow in vivo has attracted enormous interest in the biomedical community. Nevertheless, the power and general applicability of OPNMR can be vastly improved if the high nuclear spin polarization achieved in systems like xenon and helium can be efficiently transferred to the nuclear spins within substances of greater interest. Such magnetization transfer would not only provide a direct probe of the sample under study, but in principle, could vastly improve its NMR sensitivity as well.
Thus, one of our primary goals is to develop improved methods for transferring this enhanced magnetization to other systems, thereby allowing us to better “light up” the NMR of molecules, materials, and organisms. Specific applications of such polarization transfer include the study of organic inclusion complexes, probing the structure and dynamics of proteins and protein-ligand complexes, and so-called “density-matrix purification” to better enable NMR quantum computation. We are also interested in the development and application of other optical/magnetic resonance techniques, including microwave-induced optical nuclear polarization (MIONP)—whereby resonant laser and microwave radiation are combined to generate extraordinarily high polarization factors for the nuclear spins in doped organic crystals.
