动态核极化（DNP）技术是增强固体核磁共振灵敏性的强有力手段，在结构生物学和材料学等领域应用广泛。极化剂是高场DNP技术发展的关键要素，但现有基于同源双自由基的极化剂研发已面临瓶颈。申请人前期工作证实，trityl-氮氧（TN）杂化双自由基是目前最有前景的高场极化剂，但其DNP调控机制尚未明确，且性能远未最优化。为此，本项目拟通过合成结构新颖的trityl和氮氧单自由基，并调节二者间的连接链属性，以实现弛豫时间和交换相互作用等性质可调的TN双自由基的构建；采用电子顺磁共振波谱和高场DNP技术等揭示双自由基的分子结构、理化性质与DNP性能间的内在联系，筛选出性能最佳的极化剂；基于此，合成靶向半胱氨酸和脂质体的位点特异性极化剂，并以KcsA和ASR为蛋白模型探索新型极化剂在膜蛋白结构与动力学研究方面的应用潜质。本项目的有效实施将为高场极化剂研发提供理论指导,势必助力高场固体核磁共振技术的发展。

Dynamic nuclear polarization (DNP) is a powerful technique to increase sensitivity of solid-state nuclear magnetic resonance and have found wide applications in the fields of structural biology and material science. Development of new efficient polarizing agents is of crucial importance for high-field DNP. However, development of the polarizing agents based on the most commonly used homogeneous biradicals has confronted with a bottleneck. Our previous studies demonstrated that heterogeneous trityl-nitroxide (TN) biradicals are the most promising high-field polarizing agents. However, the factors controlling their DNP properties are not clear to date and thus their DNP properties are still far away from optimization. Therefore, this project will start with design and synthesis of both trityl and nitroxide monoradicals as well as modulation of the linker nature to construct a series of TN biradicals with tunable relaxation times and spin-spin exchange interactions. Then, the correlation among molecular structure, physiochemical properties and DNP properties of TN biradicals will be comprehensively explored by electron paramagnetic resonance spectroscopy and high-field DNP technique. The biradicals with the optimal DNP properties will be opted out at this stage. Finally, based on the molecular structure of the optimal biradicals, new biradicals with specific reactivity to cysteine in proteins or targeting to lipids will be further synthesized as site-specific polarizing agents. The application potential of these polarizing agents in studying structure and dynamics of membrane proteins will be explored using KcsA and ASR as protein models. The present project will shed new lights on synthesis of highly efficient high-field DNP polarizing agents and thus promote development of the high-field solid-state nuclear magnetic resonance technique.