Nuclear Magnetic Resonance Spectroscopy
The Chemistry department houses three liquid-state NMR's and one solid-state NMR.
A Varian 400-MR which is a 400 MHz NMR with an autoswitchable probe setup for running 1H, 19F, 13C, and 31P experiments.
A 2-channel 400 MHz Varian VNMRS with an ATB automation probe for running 1H, 19F, 13C, 15N, and 31P experiments. This NMR is equipped with a FTS unit for variable temperature experiments.
A 3-channel 500 MHz Varian VNMRS with a wide variety of probes that allows for the acquisition of virtually any NMR active nucleus. This NMR is equipped with a FTS unit for variable temperature experiments.
Solid-state NMR is commonly used to study materials that are insoluble in available solvents or unstable in solution.
The SIL currently operates one solid-state NMR, a 2-channel 400 MHz Tecmag Discovery with a NMR Service GmbH MAS H-X broadband probe that can rotate samples up to 18 kHz. The Discovery system is capable of running CP/MAS experiments using a 4 mm rotor.
The chemical shift that a molecule has for a particular nucleus is a function of alignment of the molecule to the external magnetic field. In liquid-state NMR the rapid rotation of a molecule in solution averages out the chemical shift to a single value called the isotropic chemical shift. In a solid-state powder sample every orientation of the sample relative to the external magnetic field is present. This can lead to peaks that are extremely broad with linewidths greater than 1000 Hz. To overcome this problem the sample is spun at the magic angle, 54.74 degrees. This averages out the chemical shift anisotropy (and dipolar couplings) and gives a high-resolution spectrum.
To spin stably within a few Hz, at a high rate, 9000-18,000 Hz, two 200-gallon compressed air tanks are used.