A Low-Spin CoII/Nitroxide Complex for Distance Measurements at Q-Band Frequencies
A Low-Spin CoII/Nitroxide Complex for Distance Measurements at Q-Band Frequencies
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DOI：
10.3390/magnetochemistry8040043
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发表时间：
2022-04
期刊：
影响因子：
2.7
通讯作者：
A. Giannoulis;D. Cordes;A. Slawin;B. Bode
中科院分区：
文献类型：
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作者：
A. Giannoulis;D. Cordes;A. Slawin;B. Bode
脉冲偶极电子顺磁共振光谱（PDS）通过纳米范围内的距离测量不断加深对化学和生物组装体的理解。新的顺磁体和脉冲序列可以提供通过其他技术无法获得的结构见解。在追求PDS的替代自旋中心，我们合成了一个低自旋CoII复合物轴承氮氧（NO）部分，其中CoII和NO的电子自旋S的1/2。我们测量了CoII-NO的距离与完善的双电子-电子共振（DEER aka PELDOR）实验，以及在Q波段频率（34 GHz）的五脉冲和六脉冲弛豫诱导偶极调制增强（RIDME）光谱。我们首先通过DEER和X射线晶体学确定了与溶液中络合物稳定性相关的挑战，并表明即使在络合物结晶不可避免的情况下，CoII-NO PDS测量也是可行的，并提供了良好的信噪比（SNR）。具体而言，DEER和五脉冲RIDME表现出约100的SNR，而六脉冲RIDME表现出受损的SNR，它帮助我们最大限度地减少了RIDME迹线中的不需要的信号。最后，我们在10 μM样品浓度下证明了RIDME。我们的研究结果表明，顺磁性CoII是一个可行的自旋中心，在中等磁场的PDS研究涉及CoII离子的机会。
Pulse dipolar electron paramagnetic resonance spectroscopy (PDS) is continuously furthering the understanding of chemical and biological assemblies through distance measurements in the nanometer range. New paramagnets and pulse sequences can provide structural insights not accessible through other techniques. In the pursuit of alternative spin centers for PDS, we synthesized a low-spin CoII complex bearing a nitroxide (NO) moiety, where both the CoII and NO have an electron spin S of 1/2. We measured CoII-NO distances with the well-established double electron–electron resonance (DEER aka PELDOR) experiment, as well as with the five- and six-pulse relaxation-induced dipolar modulation enhancement (RIDME) spectroscopies at Q-band frequencies (34 GHz). We first identified challenges related to the stability of the complex in solution via DEER and X-ray crystallography and showed that even in cases where complex disproportionation is unavoidable, CoII-NO PDS measurements are feasible and give good signal-to-noise (SNR) ratios. Specifically, DEER and five-pulse RIDME exhibited an SNR of ~100, and while the six-pulse RIDME exhibited compromised SNR, it helped us minimize unwanted signals from the RIDME traces. Last, we demonstrated RIDME at a 10 μM sample concentration. Our results demonstrate paramagnetic CoII to be a feasible spin center in medium magnetic fields with opportunities for PDS studies involving CoII ions.