In the past 15 years, magic angle spinning (MAS) dynamic nuclear polarization (DNP) has emerged as a method to increase the sensitivity of high-resolution solid-state NMR spectroscopy experiments. Recently, γ-irradiation has been used to generate significant concentrations of homogeneously distributed free radicals in a variety of solids, including quartz, glucose, and cellulose. Both γ-irradiated quartz and glucose previously showed significant MAS DNP enhancements. Here, γ-irradiation is applied to twelve small organic molecules to test the applicability of γ-irradiation as a general method of creating stable free radicals for MAS DNP experiments on organic solids and pharmaceuticals. Radical concentrations in the range of 0.25 ​mM–10 ​mM were observed in irradiated glucose, histidine, malic acid, and malonic acid, and significant ¹H DNP enhancements of 32, 130, 19, and 11 were obtained, respectively, as measured by ¹H→¹³C CPMAS experiments. However, concentrations of free radicals below 0.05 ​mM were generally observed in organic molecules containing aromatic rings, preventing sizeable DNP enhancements. DNP sensitivity gains for several of the irradiated compounds exceed that which can be obtained with the relayed DNP approach that uses exogeneous polarizing agent solutions and impregnation procedures. In several cases, significant ¹H DNP enhancements were realized at room temperature. This study demonstrates that in many cases γ-irradiation is a viable alternative to addition of stable exogenous radicals for DNP experiments on organic solids.

在过去的 15 年中，魔角旋转 (MAS) 动态核极化 (DNP) 已成为一种提高高分辨率固态 NMR 光谱实验灵敏度的方法。最近，γ-辐照已被用于在各种固体（包括石英、葡萄糖和纤维素）中产生显着浓度的均匀分布的自由基。γ 照射的石英和葡萄糖先前均显示出显着的 MAS DNP 增强。在这里，将 γ 辐照应用于 12 个有机小分子，以测试 γ 辐照作为在有机固体和药物的 MAS DNP 实验中产生稳定自由基的一般方法的适用性。在辐照的葡萄糖、组氨酸、苹果酸和丙二酸中观察到 0.25 mM–10 mM 范围内的自由基浓度，并且显着^通过1 H→ ¹³ C CPMAS 实验测量，分别获得了 32、130、19 和 11 的^{1 H DNP 增强。}然而，通常在含有芳香环的有机分子中观察到低于 0.05 mM 的自由基浓度，从而阻止了 DNP 的显着增强。几种辐照化合物的 DNP 灵敏度增益超过了使用外源极化剂溶液和浸渍程序的中继 DNP 方法所能获得的灵敏度。在一些情况下，在室温下实现了显着的^{1 H DNP 增强。}该研究表明，在许多情况下，γ-辐照是添加稳定外源自由基的可行替代方案，用于有机固体的 DNP 实验。