The overarching goal of this proposal is the development of new techniques for structure elucidation in the solid state. The PI proposes to accomplish this by exploiting dipolar couplings between nuclear spins. The strength of these couplings correlates with interatomic distances and thus provides structural information that is otherwise only accessible by diffraction techniques. The advantages of using nuclear magnetic resonance (NMR) over diffraction lie in the fact that single crystals are not required, and that the method is very sensitive to protons which are usually invisible in X-ray diffraction experiments. The PI pioneered this technique for nuclei with nuclear spin of 1/2 (such as H, C, F, P). In this proposal, the PI seeks to expand this technique to quadrupolar nuclei with a spin greater or equal than 1. In fact, most of the elements in the periodic table possess magnetically active isotopes only with quadrupolar spin. Many of these are extremely important for biological samples (Na, O) or materials research (Li, Cs, V, etc.) The PI proposes the design and construction of new NMR probes and their implementation in a series of new NMR experiments to achieve this goal.
Structure elucidation is one of the central questions in chemistry. The understanding of molecular structure helps to deduce relationships with molecular function. This knowledge is crucial for the development of new materials that enhance the quality of our lives or allow for the creation of new drugs. Structure elucidation of materials in their solid state using diffraction techniques usually requires the material to be present in their crystalline, or well-ordered, form. However, especially biological materials are often difficult to crystallize and thus tools like nuclear magnetic resonance (NMR) spectrocopy have been developed to aid in structure elucidation. NMR spectroscopy has other limitations, however, such as a much lower sensitivity, and generally, the inaccessibility of elements whose nuclei suffer from a non-spherical charge distribution. The majority of elements in the periodic table falls into this category, and includes elements of high biological relevance such as oxygen and sodium. The latter are inaccessible to atomic distance measurements by solid state NMR. Professor Gullion from West Virginia University plans to design, develop and build new instruments that will allow NMR measurements on these ubiquitous and important elements. Professor Gullion will engage the help of undergraduate, graduate, and postdoctoral students in this endeavor. He will share his technical know-how via video clips disseminated over the web, and free workshops in his laboratory. He will continue to entice our youngest generation about science through magic shows performed at the kindergarten level.
Magic-angle sample spinning nuclear magnetic resonance (MAS NMR) is an important tool for determining structures of molecules in the solid state. The structure of a molecule determines its properties, so one of the main goals of chemistry is to determine molecular structures. MAS NMR determines molecular structures through the measurement of the dipolar coupling between nuclei. We are designing MAS NMR hardware that will provide new methods to determine molecular structures via the dipolar coupling. During the course of the last grant period a prototype of a probe to measure internuclear distances was designed. MAS NMR experiments designed to measure the dipolar coupling usually apply a series of radio-frequency pulses to the sample synchronously with the sample rotation. Accordingly, control of the sample spinning speed is very important as well as is the proper orientation of the spinning sample. Other hardware developments include a novel way to control the sample spinning speed using heat and an optical lever system based on simple laser systems to monitor the angle between the sample spinning axis and magnetic field and to monitor the orientation of the probe in the bore of the magnet. Figure 1 illustrates the concept of using heat to control the sample spinning speed. The spinning speed of the sample rotor is measured and a feedback circuit adjusts the current to a heater wire to adjust the spinning speed to the desired value. MAS NMR determined the structure of cysteine, a naturally occurring amino acid, on gold nanoparticles. Because of the presumed inertness of gold there is interest in using gold nanoparticles in biological systems such as drug delivery. Cysteine is important because it is the only amino acid with a thiol group, which allows it to chemisorb to gold. It is possible, therefore, to attach peptides and proteins to gold nanoparticles by terminating them with cysteine. We determined that cysteine forms a novel bi-layer around gold nanoparticles. The inner layer is chemisorbed to gold via the thiol group. The outer layer is stabilized by hydrogen bonding to the inner layer in a tail-to-tail fashion. A stylized model of cysteine on gold nanoparticles is presented in Figure 2. The grant was used to support the research of two postdoctoral fellows, one graduate student and four undergraduate students. The postdoctoral fellows and graduate student developed new NMR hardware and determined the structure of cysteine on gold nanoparticles. The undergraduate researchers helped design new lab experiments for physical chemistry laboratories, synthesized samples, and performed physical characterization of samples (including differential scanning calorimetry and thermogravimetric analysis). A free NMR hardware workshop was presented during two summers. Approximately ten graduate students attended the workshops and received hands-on training in designing circuits relevant to NMR. A Children’s Chemistry Show was designed and presented as a service to the local community. The free chemistry show included chemical demonstrations and hands-on activities.
