Heteronuclear cross-relaxation effect modulated by the dynamics of N-functional groups in the solid state under 15N DP-MAS DNP

Heeyong Park; Boran Uluca-Yazgi; Saskia Heumann; Robert Schlögl; Josef Granwehr; Henrike Heise; P Philipp M Schleker

doi:10.1016/j.jmr.2020.106688

Heteronuclear cross-relaxation effect modulated by the dynamics of N-functional groups in the solid state under ¹⁵N DP-MAS DNP

J Magn Reson. 2020 Mar:312:106688. doi: 10.1016/j.jmr.2020.106688. Epub 2020 Jan 16.

Authors

Heeyong Park¹, Boran Uluca-Yazgi², Saskia Heumann³, Robert Schlögl⁴, Josef Granwehr⁵, Henrike Heise², P Philipp M Schleker⁶

Affiliations

¹ Max Planck Institute for Chemical Energy Conversion, Department of Heterogeneous Reactions, 45470 Mülheim an der Ruhr, Germany; Forschungszentrum Jülich, IEK-9, 52425 Jülich, Germany; RWTH Aachen University, Institute of Technical and Macromolecular Chemistry, 52074 Aachen, Germany.
² Forschungszentrum Jülich, IBI-7 and JuStruct, 52425 Jülich, Germany; Heinrich Heine Universität Düsseldorf, Institute of Physical Biology, 40225 Düsseldorf, Germany.
³ Max Planck Institute for Chemical Energy Conversion, Department of Heterogeneous Reactions, 45470 Mülheim an der Ruhr, Germany.
⁴ Max Planck Institute for Chemical Energy Conversion, Department of Heterogeneous Reactions, 45470 Mülheim an der Ruhr, Germany; Fritz Haber Institute of the Max Planck Society, 14195 Berlin, Germany.
⁵ Forschungszentrum Jülich, IEK-9, 52425 Jülich, Germany; RWTH Aachen University, Institute of Technical and Macromolecular Chemistry, 52074 Aachen, Germany.
⁶ Max Planck Institute for Chemical Energy Conversion, Department of Heterogeneous Reactions, 45470 Mülheim an der Ruhr, Germany; Forschungszentrum Jülich, IEK-9, 52425 Jülich, Germany. Electronic address: philipp.schleker@cec.mpg.de.

PMID: 32004819
DOI: 10.1016/j.jmr.2020.106688

Abstract

In a typical magic-angle spinning (MAS) dynamic nuclear polarization (DNP) nuclear magnetic resonance (NMR) experiment, several mechanisms are simultaneously involved when transferring much larger polarization of electron spins to NMR active nuclei of interest. Recently, specific cross-relaxation enhancement by active motions under DNP (SCREAM-DNP) [Daube et al. JACS 2016] has been reported as one of these mechanisms. Thereby ¹³C enhancement with inverted sign was observed in a direct polarization (DP) MAS DNP experiment, caused by reorientation dynamics of methyl that was not frozen out at 100 K. Here, we report on the spontaneous polarization transfer from hyperpolarized ¹H to both primary amine and ammonium nitrogens, resulting in an additional positive signal enhancement in the ¹⁵N NMR spectra during ¹⁵N DP-MAS DNP. The cross-relaxation induced signal enhancement (CRE) for ¹⁵N is of opposite sign compared to that observed for ¹³C due to the negative sign of the gyromagnetic ratio of ¹⁵N. The influence on CRE efficiency caused by variation of the radical solution composition and by temperature was also investigated.

Keywords: CRE; Cross-relaxation; DNP; DNP-SENS; Dynamics; N-functional group; NMR; NOE; SCREAM.

Publication types

Research Support, Non-U.S. Gov't