Heteronuclear Cross-Relaxation under Solid-State Dynamic Nuclear Polarization

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• 作者：Diane Daube ; Victoria Aladin ; Jörg Heiliger ; Johannes J. Wittmann ; Dominic Barthelmes ; Christian Bengs ; Harald Schwalbe ; Björn Corzilius
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：December 28, 2016
• 年：2016
• 卷：138
• 期：51
• 页码：16572-16575
• 全文大小：364K
• ISSN：1520-5126

文摘

We report on the spontaneous polarization transfer from dynamically hyperpolarized ¹H to ¹³C during magic-angle spinning dynamic nuclear polarization (DNP) at temperatures around 100 K. The transfer is mediated by ¹H–¹³C cross-relaxation within methyl groups due to reorientation dynamics, and results in an inverted ¹³C NMR signal of enhanced amplitude. Further spreading of transferred polarization can then occur via ¹³C–¹³C spin-diffusion. The resulting process is equal to the nuclear Overhauser effect (NOE) where typically continuous saturation of ¹H by radio frequency irradiation is employed. Here, hyperpolarization by irradiation with microwaves in the presence of typical bis-nitroxide polarizing agents is utilized for steady-state displacement of ¹H polarization from thermal equilibrium and perpetual spin-lattice relaxation. An effective ¹³C enhancement factor of up to −15 has been measured. Presence of Gd(III) furthermore amplifies the effect likely by accelerated relaxation of ¹H. We provide experimental evidence for the proposed mechanism and show that DNP-induced cross-relaxation is a robust feature within proteins and single amino acids and discuss potential applications.