PyrroTriPol: a semi-rigid trityl-nitroxide for high field dynamic nuclear polarization
Résumé
A semi-rigid trityl-nitroxide polarizing agent is introduced for magic angle spinning (MAS) dynamic nuclear polarization (DNP), which significantly broadened the scope of solid-state NMR to study biomolecular systems and materials.
Magic angle spinning (MAS) dynamic nuclear polarization (DNP) has significantly broadened the scope of
solid-state NMR to study biomolecular systems and materials. In recent years, the advent of very high
field DNP combined with fast MAS has brought new challenges in the design of polarizing agents (PA)
used to enhance nuclear spin polarization. Here, we present a trityl-nitroxide PA family based on
a piperazine linker, named PyrroTriPol, for both aqueous and organic solutions. These new radicals have
similar properties to that of TEMTriPol-I and can be readily synthesized, and purified in large quantities
thereby ensuring widespread application. The family relies on a rigid bridge connecting the trityl and the
nitroxide offering a better control of the electron spin–spin interactions thus providing improved
performance across a broad range of magnetic fields and MAS frequencies while requiring reduced
microwave power compared to bis-nitroxides. We demonstrate the efficiency of the PyrroTriPol family
under a magnetic field of 9.4, 14.1 and 18.8 T with respect to TEMTriPol-I. In particular, the superiority of
PyrroTriPol was demonstrated on g-Al2O3 nanoparticles which enabled the acquisition of a high signalto-
noise surface-selective 27Al multiple-quantum MAS experiment at 18.8 T and 40 kHz MAS frequency.
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