期刊
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
卷 22, 期 6, 页码 3643-3652出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/c9cp06201g
关键词
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资金
- National Science Foundation Division of Materials Research [DMR-1157490, 1644779]
- State of Florida
- NIH [P41 GM122698]
Nitroxide biradicals are common polarizing agents used to enhance the sensitivity of solid-state NMR experiments via Magic Angle Spinning Dynamic Nuclear Polarization (MAS-DNP). These biradicals are used to increase the polarization of protons through the cross-effect mechanism, which requires two unpaired electrons with a Larmor frequency difference greater than that of the protons. From their early conception, the relative orientation of the nitroxide rings has been identified as a critical factor determining their MAS-DNP performance. However, the MAS leads to a complex DNP mechanism with time dependent energy level anti-crossings making it difficult to pinpoint the role of relative g-tensor orientation. In this article, a single parameter called g-tensors' distance is introduced to characterize the relative orientation's impact on the MAS-DNP field profiles. It is demonstrated for the first time how the g-tensors' distance determines the nuclear hyperpolarization and depolarization properties of a given biradical. This provides a new critical parameter that paves the way for more efficient bis-nitroxides for MAS-DNP.
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