the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Optimized shaped pulses for 2D-SIFTER
Abstract. Fast and accurate arbitrary waveform generators (AWG) for generating shaped pulses in EPR have been commercially available for over a decade now. However, while the use of chirp pulses as inversion pulses in pulsed electron double resonance (PELDOR) experiments has become common, their application for generating broadband phase-sensitive transverse magnetization is not widely adopted within the community. Here we give a detailed insight into optimization procedures and instrumental challenges when using chirped pulses for broadband Fourier transform (FT) detection of electron spin echo signals, particularly the two-dimensional frequency‑correlated single frequency technique for refocusing (SIFTER) experiment. To better understand the influence of chirped pulses on the generation of broadband transverse magnetization, we investigated the phase and amplitude of chirped echoes for different time-bandwidth products while varying the number of refocusing pulses, particularly under the influence of B1‑inhomogeneity. Following our optimization procedures, we were able to perform orientation selective SIFTER measurements using rigid nitroxide spin labels on an RNA duplex. Finally, we also demonstrate the first experiments with two novel SIFTER pulse sequences, which could be of interest for the detection of either shorter or longer distances.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Magnetic Resonance.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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- RC1: 'Comment on mr-2025-11', Nino Wili, 03 Oct 2025
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CC1: 'Comment on mr-2025-11', Maxim Yulikov, 03 Oct 2025
Dear Authors, congratulations with the new manuscript. Just a comment on the background correction. You are citing our work for the SIFTER background (Vanas et al. 2023) with a statement that SIDRE decay compensates for a part of the SIFTER background. This is of course true, but this part is only 50%. Please note that in the cited paper we demonstrated theoretically that (i) the unmodulated part of the SIFTER signal has different shape than the intermolecular background contribution to the modulated part (thus, the unmodulated part needs to be subtracted before correcting the modulated part for the intermolecular background); (ii) the intermolecular background contribution for the modulated part of the SIFTER signal is half sum of the SIDRE and of the product of two Hahn echo decays going in the opposite directions. The unmodulated part of the SIFTER signal in your case (low spin concentration) should indeed be similar to the SIDRE signal, but, once again, dividing the entire SIFTER signal by the SIDRE signal is an inaccurate background correction. SIDRE decay is steeper as compared to the combination of two Hahn echoes, thus the correct intermolecular background for the modulated part of the SIFTER signal is less steep as compared to SIDRE. Accordingly, with your background correction procedure (dividing everything by SIDRE signal) you are getting artificially narrowed distance distribution. In your measurements this effect is relatively weak but visible e.g. in the Figure 10(C).
Best regards, Maxim Yulikov
Citation: https://doi.org/10.5194/mr-2025-11-CC1 - RC2: 'Comment on mr-2025-11', Daniel Klose, 07 Oct 2025
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I attached my comments as a pdf.