Ultra-wideband DEER and ESEEM on metal centers

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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.