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 17.3Å≲r≲47.0Å(0.5MHz≤d≤10MHz)\documentclass[12pt]{minimal}
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\begin{document}$$17.3 \AA \lesssim r \lesssim 47.0 \AA (0.5 \mathrm{MHz}\le d\le 10 \mathrm{MHz})$$\end{document}, where d=23D\documentclass[12pt]{minimal}
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\begin{document}$$d=\frac{2}{3}D$$\end{document}, with D\documentclass[12pt]{minimal}
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\begin{document}$$D$$\end{document} 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 0.5MHz≤d≤7.0\documentclass[12pt]{minimal}
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\begin{document}$$0.5 \mathrm{MHz}\le d \le 7.0$$\end{document} MHz. However, for d>7.0MHz\documentclass[12pt]{minimal}
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\begin{document}$$d>7.0 \mathrm{MHz}$$\end{document}, 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 t1-td\documentclass[12pt]{minimal}
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\begin{document}$${t}_{1}-{t}_{d}$$\end{document}, where t1\documentclass[12pt]{minimal}
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\begin{document}$${t}_{1}$$\end{document} is the time of the echo after the second pulse and td\documentclass[12pt]{minimal}
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\begin{document}$${t}_{d}$$\end{document} is the dead time, still provides undistorted Pake doublets centered at ±d\documentclass[12pt]{minimal}
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\begin{document}$$\pm d$$\end{document}. 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 T2S\documentclass[12pt]{minimal}
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\begin{document}$${T}_{2}^{S}$$\end{document}, the spin–spin relaxation time over the p=±1\documentclass[12pt]{minimal}
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\begin{document}$$p=\pm 1$$\end{document} coherence pathways.
