Preprints
https://doi.org/10.5194/mr-2024-14
https://doi.org/10.5194/mr-2024-14
10 Sep 2024
 | 10 Sep 2024
Status: a revised version of this preprint was accepted for the journal MR and is expected to appear here in due course.

Increased sensitivity in Electron Nuclear Double Resonance spectroscopy with chirped radiofrequency pulses

Julian Stropp, Nino Wili, Niels Christian Nielsen, and Daniel Klose

Abstract. Electron Nuclear Double Resonance (ENDOR) spectroscopy is an EPR technique to detect the nuclear frequency spectra of hyperfine coupled nuclei close to paramagnetic centres, which have interactions that are not resolved in continuous wave EPR spectra and may be fast relaxing on the time scale of NMR. For the common case of non-crystalline solids, such as powders or frozen solutions of transition metal complexes, the anisotropy of the hyperfine and nuclear quadrupole interactions renders ENDOR lines often several MHz broad, thus diminishing intensity. With commonly used ENDOR pulse sequences only a small fraction of the NMR/ENDOR line is excited with a typical RF pulse length of several tens of μs, and this limits the sensitivity in conventional ENDOR experiments. In this work, we show the benefit of chirped RF excitation in frequency domain ENDOR as a simple yet effective way to significantly improve sensitivity. We demonstrate on a frozen solution of Cu(II)-tetraphenylporphyrin that the intensity of broad copper and nitrogen ENDOR lines increases up to 9-fold compared to single frequency RF excitation, thus making the detection of metal ENDOR spectra more feasible. The tunable bandwidth of the chirp RF pulses allows the operator to optimize for sensitivity and choose a tradeoff with resolution, opening up options previously inaccessible in ENDOR spectroscopy. Also, chirp pulses help to reduce RF amplifier overtones, since lower RF powers suffice to achieve intensities matching conventional ENDOR. In 2D TRIPLE experiments the signal increase exceeds 10 times for some lines, thus making chirped 2D TRIPLE experiments feasible even for broad peaks in manageable acquisition times.

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 preprint. The responsibility to include appropriate place names lies with the authors.
Julian Stropp, Nino Wili, Niels Christian Nielsen, and Daniel Klose

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on mr-2024-14', Fabian Hecker, 02 Oct 2024
    • AC1: 'Reply on CC1', Daniel Klose, 07 Oct 2024
  • RC1: 'Comment on mr-2024-14', Anonymous Referee #1, 04 Oct 2024
    • AC2: 'Reply to RC1', Daniel Klose, 08 Oct 2024
      • AC4: 'Reply on AC2', Daniel Klose, 25 Oct 2024
  • RC2: 'Comment on mr-2024-14', Anonymous Referee #2, 19 Oct 2024
    • AC3: 'Reply on RC2', Daniel Klose, 25 Oct 2024

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on mr-2024-14', Fabian Hecker, 02 Oct 2024
    • AC1: 'Reply on CC1', Daniel Klose, 07 Oct 2024
  • RC1: 'Comment on mr-2024-14', Anonymous Referee #1, 04 Oct 2024
    • AC2: 'Reply to RC1', Daniel Klose, 08 Oct 2024
      • AC4: 'Reply on AC2', Daniel Klose, 25 Oct 2024
  • RC2: 'Comment on mr-2024-14', Anonymous Referee #2, 19 Oct 2024
    • AC3: 'Reply on RC2', Daniel Klose, 25 Oct 2024
Julian Stropp, Nino Wili, Niels Christian Nielsen, and Daniel Klose
Julian Stropp, Nino Wili, Niels Christian Nielsen, and Daniel Klose

Viewed

Total article views: 503 (including HTML, PDF, and XML)
HTML PDF XML Total Supplement BibTeX EndNote
273 75 155 503 24 9 6
  • HTML: 273
  • PDF: 75
  • XML: 155
  • Total: 503
  • Supplement: 24
  • BibTeX: 9
  • EndNote: 6
Views and downloads (calculated since 10 Sep 2024)
Cumulative views and downloads (calculated since 10 Sep 2024)

Viewed (geographical distribution)

Total article views: 456 (including HTML, PDF, and XML) Thereof 456 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 
Latest update: 29 Nov 2024
Download
Short summary
Sensitivity is often the limiting factor in ENDOR. Here, we demonstrate how using chirp radiofrequency pulses can improve ENDOR sensitivity up to 3-9-fold, with the strongest increase for broader lines often encountered in disordered solids for nuclei such as nitrogen and metals. The resulting drastic speed-up in acquisition times renders also 2D ENDOR more feasible, as we demonstrate in 2D TRIPLE showing correlations of Cu hyperfine couplings.