Ultra-wideband DEER and ESEEM on metal centers

大于500 MHz的激励带宽可以在脉冲EPR实验中提供实质性的灵敏度增强，并且最近在任意波形激励下变得可行。在这个项目中，我们将为两个关键实验开发这样的方法，使它们适用于蛋白质样品。为了提高纳米范围内金属-金属DEER距离分布测量的灵敏度，我们将依靠超宽带（UWB）技术、啁啾泵浦脉冲调制深度增强、啁啾回波观测者序列的组合，以及对于S > 1/2金属中心（如Gd(III)），通过卫星跃迁的人口转移来实现中心跃迁的预极化。期望从超宽带回波序列检测中获得进一步的灵敏度增益。通过超宽带二维FT-EPR相关的ESEEM和三维FT-EPR相关的HYSCORE实验，我们可以测量到100 MHz以上的金属核频率。这些实验将扩展到微晶粉末和Cu2+， VO2+和Mn2+中心的玻璃状冷冻溶液，并最终在双核Mn(III)-Mn（IV）配合物上进行测试，该配合物具有多线EPR光谱，如果没有额外的实验信息，则无法完全分析。

Excitation bandwidths larger than 500 MHz can provide substantial sensitivity enhancements in pulse EPR experiments and have recently become feasible with arbitrary waveform excitation. In this project we will develop such approaches for two key experiments to a point where they become applicable to protein samples. To enhance sensitivity in metal-metal DEER distance distribution measurements in the nanometer range we shall rely on a combination of ultra-wideband (UWB) techniques, chirp pump pulses for modulation depth enhancement, a chirp echo observer sequence, and, for S > 1/2 metal centers such as Gd(III), pre-polarization of the central transition by population transfer from satellite transitions. Further sensitivity gain is expected from UWB echo train detection. By UWB 2D FT-EPR correlated ESEEM and 3D FT-EPR correlated HYSCORE experiments we can measure metal nuclear frequencies exceeding 100 MHz. These experiments will be extended to microcrystalline powders and glassy frozen solutions for Cu2+, VO2+, and Mn2+ centers and ultimately be tested on a binuclear Mn(III)-Mn(IV) complex that features a multiline EPR spectrum of a type that cannot be fully analyzed without additional experimental information.