Wili Nino, Nielsen Anders Bodholt, Völker Laura Alicia, Schreder Lukas, Nielsen Niels Chr, Jeschke Gunnar, Tan Kong Ooi
Department of Chemistry and Applied Biosciences, Laboratory of Physical Chemistry, ETH Zurich, Vladimir-Prelog-Weg 2, 8093 Zurich, Switzerland.
Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, DK-8000 Aarhus C, Denmark.
Sci Adv. 2022 Jul 15;8(28):eabq0536. doi: 10.1126/sciadv.abq0536.
Dynamic nuclear polarization (DNP) is a nuclear magnetic resonance (NMR) hyperpolarization technique that mediates polarization transfer from unpaired electrons with large thermal polarization to NMR-active nuclei via microwave (mw) irradiation. The ability to generate arbitrarily shaped mw pulses using arbitrary waveform generators allows for remarkable improvement of the robustness and versatility of DNP. We present here novel design principles based on single-spin vector effective Hamiltonian theory to develop new broadband DNP pulse sequences, namely, an adiabatic version of XiX (X-inverse X)-DNP and a broadband excitation by amplitude modulation (BEAM)-DNP experiment. We demonstrate that the adiabatic BEAM-DNP pulse sequence may achieve a H enhancement factor of ∼360, which is better than ramped-amplitude NOVEL (nuclear spin orientation via electron spin locking) at ∼0.35 T and 80 K in static solids doped with trityl radicals. In addition, the bandwidth of the BEAM-DNP experiments (~50 MHz) is about three times the H Larmor frequency. The generality of our theoretical approach will be helpful in the development of new pulsed DNP sequences.
动态核极化（DNP）是一种核磁共振（NMR）超极化技术，它通过微波（mw）辐射介导未配对电子的极化转移，这些未配对电子具有大的热极化，转移至具有NMR活性的原子核。使用任意波形发生器生成任意形状的mw脉冲的能力，使得DNP的稳健性和通用性得到显著提高。我们在此基于单自旋矢量有效哈密顿理论提出新颖的设计原则，以开发新的宽带DNP脉冲序列，即绝热版的XiX（X逆X）-DNP和幅度调制宽带激发（BEAM）-DNP实验。我们证明，绝热BEAM-DNP脉冲序列可实现约360的H增强因子，这在掺杂三苯甲基自由基的静态固体中，于约0.35 T和80 K时优于斜坡幅度NOVEL（通过电子自旋锁定实现核自旋取向）。此外，BEAM-DNP实验的带宽（约50 MHz）约为H拉莫尔频率的三倍。我们理论方法的通用性将有助于新型脉冲DNP序列的开发。
