Abstract：
We present field-domain rapid-scan (RS) electron paramagnetic resonance (EPR) at 8.6T and 240GHz. To enable this technique, we upgraded a home-built EPR spectrometer with an FPGA-enabled digitizer and real-time processing software. The software leverages the Hilbert transform to recover the in-phase (I) and quadrature (Q) channels, and therefore the raw absorptive and dispersive signals, χ\' and χ\'\', from their combined magnitude (I2+Q2). Averaging a magnitude is simpler than real-time coherent averaging and has the added benefit of permitting long-timescale signal averaging (up to at least 2.5×106 scans) because it eliminates the effects of source-receiver phase drift. Our rapid-scan (RS) EPR provides a signal-to-noise ratio that is approximately twice that of continuous wave (CW) EPR under the same experimental conditions, after scaling by the square root of acquisition time. We apply our RS EPR as an extension of the recently reported time-resolved Gd-Gd EPR (TiGGER) [Maity et al., 2023], which is able to monitor inter-residue distance changes during the photocycle of a photoresponsive protein through changes in the Gd-Gd dipolar couplings. RS, opposed to CW, returns field-swept spectra as a function of time with 10ms time resolution, and thus, adds a second dimension to the static field transients recorded by TiGGER. We were able to use RS TiGGER to track time-dependent and temperature-dependent kinetics of AsLOV2, a light-activated phototropin domain found in oats. The results presented here combine the benefits of RS EPR with the improved spectral resolution and sensitivity of Gd chelates at high magnetic fields. In the future, field-domain RS EPR at high magnetic fields may enable studies of other real-time kinetic processes with time resolutions that are otherwise difficult to access in the solution state.
摘要：
我们提出了在8.6T和240GHz下的场域快速扫描（RS）电子顺磁共振（EPR）。要启用此技术，我们升级了家用EPR光谱仪与FPGA启用的数字化仪和实时处理软件。该软件利用希尔伯特变换来恢复同相(I)和正交(Q)通道，因此原始的吸收和分散信号，χ\'和χ\'\'，从它们的组合大小(I2+Q2)。平均幅度比实时相干平均更简单,并且具有允许长时间尺度信号平均(高达至少2.5X106扫描)的附加益处,因为其消除了源-接收器相位漂移的影响。在相同的实验条件下，我们的快速扫描（RS）EPR提供的信噪比约为连续波（CW）EPR的两倍。按采集时间的平方根缩放后。我们应用RSEPR作为最近报道的时间分辨Gd-GdEPR（TiGGER）的扩展[Maity等人。,2023],它能够通过Gd-Gd偶极偶联的变化来监测光响应蛋白光循环过程中残基间距离的变化。RS,反对CW，以10ms的时间分辨率返回场扫描光谱作为时间的函数，因此，为TiGGER记录的静态场瞬态添加了第二个维度。我们能够使用RSTiGGER跟踪AsLOV2的时间依赖性和温度依赖性动力学，AsLOV2是燕麦中发现的光活化的光促激素域。此处呈现的结果将RSEPR的益处与Gd螯合物在高磁场下的改进的光谱分辨率和灵敏度相结合。在未来,磁场域RSEPR在高磁场可以使其他实时动力学过程的研究与时间分辨率，否则很难在溶液状态访问。
