Bridging DNP and MAS NMR dipolar recoupling -- from static single crystal to spinning powders

TL;DR

This paper introduces a formalism that simplifies the design of NMR experiments by translating static single-crystal optimizations to spinning powders, enabling broadband dipolar recoupling sequences across different NMR techniques.

Contribution

It demonstrates that static-sample optimizations can be effectively applied to spinning powders and pulse sequences can be exchanged between static and MAS NMR, advancing experimental design.

Findings

Designed broadband heteronuclear dipolar recoupling experiments

Implemented ultra-broadband 13C-15N and 2H-13C cross-polarization sequences

Validated the approach on various RF irradiation schemes

Abstract

Spin engineering of advanced pulse sequences has had a transformative impact on the development of nuclear magnetic resonance (NMR) spectroscopy, to an extending degree also electron paramagnetic resonance (EPR), and the hybrid between the two, dynamic nuclear polarization (DNP). Based on a simple formalism, we demonstrate that (i) single-crystal static-sample optimisations may tremendously ease design of experiments for rotating powders and (ii) pulse sequences may readily be exchanged between these distinct spectroscopies. Specifically, we design broadband heteronuclear solid-state NMR magic-angle-spinning (MAS) dipolar recoupling experiments based on the recently developed PLATO (PoLarizAtion Transfer via non-linear Optimization) microwave (MW) pulse sequence optimized on a single crystal for powder static-sample DNP. Using this concept, we demonstrate design of ultra-broadband 13C-15N and 2H-13C cross-polarization experiments, using PLATO on the 13C radio-frequency (RF) channel and square/ramped or RESPIRATION (Rotor Echo Short Pulse IRrAdiaTION) RF irradiation on the 15N and 2H RF channels, respectively.