A Low-Spin CoII/Nitroxide Complex for Distance Measurements at Q-Band Frequencies

Pulse dipolar electron paramagnetic resonance spectroscopy (PDS) is continuously furthering the understanding of chemical and biological assemblies through distance measurements in nanometer range. New paramagnets pulse sequences can provide structural insights not accessible other techniques. In pursuit alternative spin centers for PDS, we synthesized a low-spin CoII complex bearing nitroxide (NO) moiety, where both NO have an S 1/2. We measured CoII-NO distances with well-established double electron–electron (DEER aka PELDOR) experiment, as well five- six-pulse relaxation-induced modulation enhancement (RIDME) spectroscopies at Q-band frequencies (34 GHz). first identified challenges related to stability solution via DEER X-ray crystallography showed that even cases disproportionation unavoidable, PDS are feasible give good signal-to-noise (SNR) ratios. Specifically, five-pulse RIDME exhibited SNR ~100, while compromised SNR, it helped us minimize unwanted signals from traces. Last, demonstrated 10 μM sample concentration. Our results demonstrate be center medium magnetic fields opportunities studies involving ions.