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Low Cost, Versatile NMR Instrumentation Development
A basic NMR probe is a resonance circuit used to deliver radio-power to a sample and to detect the resulting radiofrequency signal. Transmission-line NMR probes (panel a, left) represent a low-cost design that can be constructed from materials that are mostly available at a hardware stores. However, they suffer from a similar drawback to many commercial probes: they are built to handle only a limited set of nuclei in a specific magnetic field. To overcome this difficulty, our lab is designing a "universal NMR probe kit" which will allow the assembly of a probe of arbitrary frequency capabilities from a set of short, screw-together segments (panel a, right). Where an arbitrary frequency capability using commercially available products would require multiple probes, each costing >$200,000, the universal probe kit will allow a laboratory to perform NMR with essentially any combination of nuclei in in essentially any magnetic field for <$10,000. Students will design NMR probes (a basic probe circuit is illustrated in panel b of the figure), test their radiofrequency (RF) properties, and perform a wide range of NMR experiments using them. In biological applications, this means moving beyond the ¹H, ¹³C, and ¹⁵N traditionally used for NMR. In inorganic applications, it will allow us to study a wide range of different samples without having to purchase expensive instrumentation.
NMR Simulation Methods
Simulations in NMR serve both to predict the outcome of what may be a lengthy experiment and to assist with interpretation of data that has already been collected. This boils down to solving the Liouville-von-Neumann Equation (panel a, top) for the density matrix, a differential equation describing the evolution of the density matrix, a matrix containing the information about the orientation of the spins in the sample. We are developing methods to accelerate NMR simulations by investigating improved numerical solutions to differential equations and numerical integration of Euler angles (panel a, bottom). We use PYTHON and MATLAB to perform numerical simulations of NMR phenomena, as well as the commercial spin package SPINEVOLUTION. Panel b of the figure illustrates a couple of examples. On the right is a simulation of ¹³C spectra of an amino acid at various MAS frequencies calculated in PYTHON. On the right are spectra of amorphous Al₂O₃ simulated using SPINEVOLUTION. The blue trace was simulated as being under 25 kHz MAS in 13.85T field, while the orange was simulated without MAS at 47.00 T. The numbers above each resonance indicate the varying coordination number of the Al sites. Students will learn and develop NMR simulation, computer programming, and numerical problem-solving methods.
Metallothionein Structures
Metallothioneins are a class of proteins that serve a variety of functions throughout the body. These include chelation of heavy metals, regulation of zinc and copper levels in the body, and controlling the permeability of the mitochondrial inner membrane, among others. This range of functions is facilitated by the ability of metallothioneins to bind a wide range of different metal centers including Cd, Zn, Cu, Se, Hg, Ag, As, Pb. All of these have NMR active isotopes, many of wich are more sensitive and abundant than the more commonly used ¹⁵N nucleus. We will use these metal centers to obtain high resolutions structural information about the metallothioneins in the vicinity of the metal binding sites. The two PDB structures shown in the figure are the only two human metallothionein structures in the PDB. They are the α (a) and ß (b) domains of metallothionein-2 bound to cadmium. With 4 different human metallothioneins and a wide range of different metal centers, there is significant room for expanding the PDB structures available. Students will learn protein structrual determination methods using solid-state NMR.
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