Category Archives: Simulations

Instrumentation for solid-state dynamic nuclear polarization with magic angle spinning NMR

Rosay, M., M. Blank, and F. Engelke, Instrumentation for solid-state dynamic nuclear polarization with magic angle spinning NMR. J Magn Reson, 2016. 264: p. 88-98.

http://www.ncbi.nlm.nih.gov/pubmed/26920834

Advances in dynamic nuclear polarization (DNP) instrumentation and methodology have been key factors in the recent growth of solid-state DNP NMR applications. We review the current state of the art of solid-state DNP NMR instrumentation primarily based on available commercial platforms. We start with a general system overview, including options for microwave sources and DNP NMR probes, and then focus on specific developments for DNP at 100K with magic angle spinning (MAS). Gyrotron microwave sources, passive components to transmit microwaves, the DNP MAS probe, a cooling device for low-temperature MAS, and sample preparation procedures including radicals for DNP are considered.

Solid effect DNP polarization dynamics in a system of many spins

Wisniewski, D., et al., Solid effect DNP polarization dynamics in a system of many spins. J Magn Reson, 2016. 264: p. 30-8.

http://www.ncbi.nlm.nih.gov/pubmed/26920828

We discuss the polarization dynamics during solid effect dynamic nuclear polarization (DNP) in a central spin model that consists of an electron surrounded by many nuclei. To this end we use a recently developed formalism and validate first its performance by comparing its predictions to results obtained by solving the Liouville von Neumann master equation. The use of a Monte Carlo method in our formalism makes it possible to significantly increase the number of spins considered in the model system. We then analyse the dependence of the nuclear bulk polarization on the presence of nuclei in the vicinity of the electron and demonstrate that increasing the minimal distance between nuclei and electrons leads to a rise of the nuclear bulk polarization. These observations have implications for the design of radicals that can lead to improved values of nuclear spin polarization. Furthermore, we discuss the potential to extend our formalism to more complex spin systems such as cross effect DNP.

Frequency swept microwaves for hyperfine decoupling and time domain dynamic nuclear polarization

Hoff, D.E., et al., Frequency swept microwaves for hyperfine decoupling and time domain dynamic nuclear polarization. Solid State Nucl Magn Reson, 2015.

http://www.ncbi.nlm.nih.gov/pubmed/26482131

Hyperfine decoupling and pulsed dynamic nuclear polarization (DNP) are promising techniques to improve high field DNP NMR. We explore experimental and theoretical considerations to implement them with magic angle spinning (MAS). Microwave field simulations using the high frequency structural simulator (HFSS) software suite are performed to characterize the inhomogeneous phase independent microwave field throughout a 198GHz MAS DNP probe. Our calculations show that a microwave power input of 17W is required to generate an average EPR nutation frequency of 0.84MHz. We also present a detailed calculation of microwave heating from the HFSS parameters and find that 7.1% of the incident microwave power contributes to dielectric sample heating. Voltage tunable gyrotron oscillators are proposed as a class of frequency agile microwave sources to generate microwave frequency sweeps required for the frequency modulated cross effect, electron spin inversions, and hyperfine decoupling. Electron spin inversions of stable organic radicals are simulated with SPINEVOLUTION using the inhomogeneous microwave fields calculated by HFSS. We calculate an electron spin inversion efficiency of 56% at a spinning frequency of 5kHz. Finally, we demonstrate gyrotron acceleration potentials required to generate swept microwave frequency profiles for the frequency modulated cross effect and electron spin inversions.

Have a question?

If you have questions about our instrumentation or how we can help you, please contact us.