Tan Kong Ooi, Yang Chen, Weber Ralph T, Mathies Guinevere, Griffin Robert G
Francis Bitter Magnet Laboratory and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Bruker BioSpin Corporation, Billerica, MA 01821, USA.
Sci Adv. 2019 Jan 18;5(1):eaav6909. doi: 10.1126/sciadv.aav6909. eCollection 2019 Jan.
Pulsed dynamic nuclear polarization (DNP) techniques can accomplish electron-nuclear polarization transfer efficiently with an enhancement factor that is independent of the Zeeman field. However, they often require large Rabi frequencies and, therefore, high-power microwave irradiation. Here, we propose a new low-power DNP sequence for static samples that is composed of a train of microwave pulses of length τ spaced with delays . A particularly robust DNP condition using a period τ = τ + set to ~1.25 times the Larmor period τ is investigated which is a time-optimized pulsed DNP sequence (TOP-DNP). At 0.35 T, we obtained an enhancement of ~200 using TOP-DNP compared to ~172 with nuclear spin orientation via electron spin locking (NOVEL), a commonly used pulsed DNP sequence, while using only ~7% microwave power required for NOVEL. Experimental data and simulations at higher fields suggest a field-independent enhancement factor, as predicted by the effective Hamiltonian.
脉冲动态核极化（DNP）技术能够以与塞曼场无关的增强因子高效地实现电子 - 核极化转移。然而，它们通常需要较大的拉比频率，因此需要高功率微波辐射。在此，我们提出一种用于静态样品的新型低功率DNP序列，该序列由一系列长度为τ且间隔为 的微波脉冲组成。研究了一种特别稳健的DNP条件，使用设置为拉莫尔周期τ的约1.25倍的周期τ = τ + ，这是一种时间优化的脉冲DNP序列（TOP - DNP）。在0.35 T时，与通过电子自旋锁定实现核自旋取向（NOVEL，一种常用的脉冲DNP序列）相比，使用TOP - DNP我们获得了约200的增强，而仅使用NOVEL所需微波功率的约7％。更高场强下的实验数据和模拟表明，如有效哈密顿量所预测的那样，增强因子与场强无关。
