The feasibility of one-dimensional two-pulse correlation spectroscopy (COSY) Electron Paramagnetic Resonance (EPR) sequence for distance measurements in biological systems using nitroxide biradicals is investigated numerically at Ku-band. It is found that the COSY sequences can be exploited to measure distances between the two nitroxides in the range \(17.3 \AA \lesssim r \lesssim 47.0 \AA (0.5 \mathrm{MHz}\le d\le 10 \mathrm{MHz})\), where \(d=\frac{2}{3}D\), with \(D\) being the dipolar-coupling constant. Taking into account the dead time after the second pulse, it is found that the modulation depth can only be measured for \(0.5 \mathrm{MHz}\le d \le 7.0\) MHz. However, for \(d>7.0 \mathrm{MHz}\), for which a significant part of the initial signal is lost in the dead time, the Fourier transform of the observable part of the signal after the dead time as a function of \({t}_{1}-{t}_{d}\), where \({t}_{1}\) is the time of the echo after the second pulse and \({t}_{d}\) is the dead time, still provides undistorted Pake doublets centered at \(\pm d\). It is shown here numerically that the amplitudes of the Pake doublets of the COSY signal are the most intense, one-to-two orders of magnitude larger, as compared to those of the four-, five-, six- pulse double quantum coherence (DQC), two-pulse double quantum (DQ), and five-pulse DQM (double quantum modulation) sequences. Another advantage of the COSY technique is that it provides a measurement of \({T}_{2}^{S}\), the spin–spin relaxation time over the \(p=\pm 1\) coherence pathways.

一维二维相关光谱 (COSY) 电子顺磁共振 (EPR) 序列在使用氮氧双自由基的生物系统中进行距离测量的可行性在 Ku 波段进行了数值研究。发现可以利用 COZY 序列来测量范围内的两个氮氧化物之间的距离\(17.3 \AA \lesssim r \lesssim 47.0 \AA (0.5 \mathrm{MHz}\le d\le 10 \mathrm{MHz })\)，其中\(d=\frac{2}{3}D\)，其中\(D\)是偶极耦合常数。考虑到第二个脉冲后的死区时间，发现调制深度只能在\(0.5 \mathrm{MHz}\le d \le 7.0\) MHz 下测量。然而，对于\(d>7.0 \mathrm{MHz}\)，对于初始信号的重要部分在死区时间丢失，死区时间后信号的可观察部分的傅立叶变换作为\({t}_{1}-{t}_{ d}\)，其中\({t}_{1}\)是第二个脉冲后的回波时间，\({t}_{d}\)是死区时间，仍然提供未失真的 Pake doublets 中心在\(\pm d\). 这里用数字显示，与四、五、六脉冲双量子相干的幅度相比，COZY 信号的 Pake 双峰的幅度最强，大一到两个数量级（ DQC)、双脉冲双量子 (DQ) 和五脉冲 DQM（双量子调制）序列。COZY 技术的另一个优点是它提供了\({T}_{2}^{S}\)的测量值，即\(p=\pm 1\)相干路径上的自旋-自旋弛豫时间。