Fred Mentink-Vigier

Florida State Univeristy and the Maglab

Hosted by: Dr. Perras

Title:

How theory enables the design of better biradicals: the case of perdeuterated AsymPol and PyrroTriPol

Abstract:

Magic Angle Spinning Dynamic Nuclear Polarization (MAS-DNP) enables solid-state NMR experiments on chemical systems with low nuclear spin concentration. It commonly relies on organic biradicals to quickly generate high ¹H spin polarization and many research groups have develop better biradicals. As of today, more efficient and chemically stable biradicals are needed to expand the scope of MAS-DNP. In addition, the exact role of biradicals' protons in the DNP mechanism, and how they contribute to the spread of the hyperpolarization within the (ill-named) spin-diffusion barrier, remain debated in the community. To make better biradicals and understand those fundamental problems, the development of quantitative simulations using a large scale spin model is needed. In this talk we demonstrate the prediction of MAS-DNP performance on a series of biradicals dubbed bTureas when combined with DFT, Molecular Dynamics and multifrequency EPR. This approach is subsequently used to explain how the AsymPols biradicals can generate fast build up times and further used to explore the roles of the biradicals’ protons. Unlike other biradicals, the AsymPols directly hyperpolarize the surrounding solvent ¹H, which means that perdeuterated forms of AsymPol lead to higher hyperpolarization and unchanged T_b.

Finally, DFT and MD guided the design of a new hetero-biradical family, the PyrroTriPols, that are more efficient for high field MAS-DNP. The PyrroTriPol structure overcomes the low synthetic yield, moderate stabilities, and chemical bridge flexibility of other current hetero-biradicals. PyrroTriPol and PyrroTriPol-OMe, soluble in water and organic solvents respectively, demonstrated very high DNP efficiency at all fields tested. In addition, both radicals were found to work well with low microwave amplitudes, making them candidates for DNP with low-power microwaves sources.

Bio:

Frederic Mentink-Vigier obtained his master’s degree from the “Ecole National Superieure de Chimie ParisTech” in 2008 that covered both organic synthesis and material science. He earned his PhD in 2011 working at the condensed matter laboratory (Univ. Paris 6) working on semi-conductors for quantum computing, under the supervision of Pr. L. Binet and D. Gourier. He then worked as a post-doctoral fellow under the joint supervision of Pr. D. Goldfarb and S. Vega, at the Weizmann Institute of Science, where he became a worldwide expert in MAS-DNP. He joined the group of Dr. Gael De Paepe in 2014 to work on biradical design and MAS-DNP with helium spinning. Since 2016, he works at the National High Magnetic Field Laboratory and directs the MAS-DNP research program.