Optimal efficiency of dissolution dynamic nuclear polarization (DNP) is essential to provide the required high sensitivity enhancements for in vitro and in vivo hyperpolarized ¹³C nuclear magnetic resonance (NMR) spectroscopy and imaging (MRI). At the nexus of the DNP process are the free electrons, which provide the high spin alignment that is transferred to the nuclear spins. Without changing DNP instrumental conditions, one way to improve ¹³C DNP efficiency is by adding trace amounts of paramagnetic additives such as lanthanide (e.g., Gd³⁺, Ho³⁺, Dy³⁺, Tb³⁺) complexes to the DNP sample, which has been observed to increase solid-state ¹³C DNP signals by 100–250%. Herein, we have investigated the effects of paramagnetic transition metal complex R-NOTA (R = Mn²⁺, Cu²⁺, Co²⁺) doping on the efficiency of ¹³C DNP using trityl OX063 as the polarizing agent. Our DNP results at 3.35 T and 1.2 K show that doping the ¹³C sample with 3 mM Mn²⁺-NOTA led to a substantial improvement of the solid-state ¹³C DNP signal by a factor of nearly 3. However, the other transition metal complexes Cu²⁺-NOTA and Co²⁺-NOTA complexes, despite their paramagnetic nature, had essentially no impact on solid-state ¹³C DNP enhancement. W-band electron paramagnetic resonance (EPR) measurements reveal that the trityl OX063 electron T₁ was significantly reduced in Mn²⁺-doped samples but not in Cu²⁺- and Co²⁺-doped DNP samples. This work demonstrates, for the first time, that not all paramagnetic additives are beneficial to DNP. In particular, our work provides a direct evidence that electron T₁ reduction of the polarizing agent by a paramagnetic additive is an essential requirement for the improvement seen in solid-state ¹³C DNP signal.

中文翻译：

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过渡金属掺杂揭示了电子T ₁还原与¹³ C动态核极化效率之间的联系

溶出动态核极化（DNP）的最佳效率对于为体外和体内超极化¹³ C核磁共振（NMR）光谱和成像（MRI）提供所需的高灵敏度增强至关重要。在DNP过程的核心是自由电子，自由电子提供了高自旋排列，并转移到核自旋上。在不改变DNP仪器条件的情况下，提高¹³ C DNP效率的一种方法是通过添加痕量顺磁性添加剂，例如镧系元素（例如Gd ³⁺，Ho ³⁺，Dy ³⁺，Tb ³⁺）与DNP样品形成络合物，据观察，该样品可将固态¹³ C DNP信号增加100–250％。在本文中，我们研究了使用三苯甲基OX063作为偏振剂的顺磁性过渡金属络合物R-NOTA（R = Mn 2 ⁺，Cu 2 ⁺，Co ²⁺）掺杂对¹³ C DNP效率的影响。我们在3.35 T和1.2 K下的DNP结果表明，用3 mM Mn ²⁺ -NOTA掺杂¹³ C样品可将固态¹³ C DNP信号显着提高近3倍。金属配合物Cu ²⁺ -NOTA和Co ²⁺-NOTA配合物，尽管具有顺磁性，但对固态¹³ C DNP增强基本上没有影响。W波段电子顺磁共振（EPR）测量表明，在掺杂Mn ^2+的样品中三苯甲基OX063电子T ₁显着降低，而在掺杂Cu ²⁺和Co ^2+的DNP样品中三苯甲基OX063电子T ₁并未显着降低。这项工作首次证明并非所有顺磁性添加剂都对DNP有益。特别地，我们的工作提供了直接的证据，表明顺磁性添加剂对电子T ₁的偏振剂还原是固态¹³ C DNP信号改善的基本要求。