Improved sensitivity for W-band Gd(III)-Gd(III) and nitroxide-nitroxide DEER measurements with shaped pulses

Thorsten Bahrenberg; Yael Rosenski; Raanan Carmieli; Koby Zibzener; Mian Qi; Veronica Frydman; Adelheid Godt; Daniella Goldfarb; Akiva Feintuch

doi:10.1016/j.jmr.2017.08.003

Improved sensitivity for W-band Gd(III)-Gd(III) and nitroxide-nitroxide DEER measurements with shaped pulses

J Magn Reson. 2017 Oct:283:1-13. doi: 10.1016/j.jmr.2017.08.003. Epub 2017 Aug 10.

Authors

Thorsten Bahrenberg¹, Yael Rosenski¹, Raanan Carmieli², Koby Zibzener¹, Mian Qi³, Veronica Frydman², Adelheid Godt³, Daniella Goldfarb¹, Akiva Feintuch⁴

Affiliations

¹ Department of Chemical Physics, Weizmann Institute of Science, 76100 Rehovot, Israel.
² Department of Chemical Research Support, Weizmann Institute of Science, 76100 Rehovot, Israel.
³ Faculty of Chemistry and Center for Molecular Materials (CM(2)), Bielefeld University, 33615 Bielefeld, Germany.
⁴ Department of Chemical Physics, Weizmann Institute of Science, 76100 Rehovot, Israel. Electronic address: akiva.feintuch@weizmann.ac.il.

PMID: 28834777
DOI: 10.1016/j.jmr.2017.08.003

Abstract

Chirp and shaped pulses have been recently shown to be highly advantageous for improving sensitivity in DEER (double electron-electron resonance, also called PELDOR) measurements due to their large excitation bandwidth. The implementation of such pulses for pulse EPR has become feasible due to the availability of arbitrary waveform generators (AWG) with high sampling rates to support pulse shaping for pulses with tens of nanoseconds duration. Here we present a setup for obtaining chirp pulses on our home-built W-band (95GHz) spectrometer and demonstrate its performance on Gd(III)-Gd(III) and nitroxide-nitroxide DEER measurements. We carried out an extensive optimization procedure on two model systems, Gd(III)-PyMTA-spacer-Gd(III)-PyMTA (Gd-PyMTA ruler; zero-field splitting parameter (ZFS) D∼1150MHz) as well as nitroxide-spacer-nitroxide (nitroxide ruler) to evaluate the applicability of shaped pulses to Gd(III) complexes and nitroxides, which are two important classes of spin labels used in modern DEER/EPR experiments. We applied our findings to ubiquitin, doubly labeled with Gd-DOTA-monoamide (D∼550MHz) asa model for a system with a small ZFS. Our experiments were focused on the questions (i) what are the best conditions for positioning of the detection frequency, (ii) which pump pulse parameters (bandwidth, positioning in the spectrum, length) yield the best signal-to-noise ratio (SNR) improvements when compared to classical DEER, and (iii) how do the sample's spectral parameters influence the experiment. For the nitroxide ruler, we report an improvement of up to 1.9 in total SNR, while for the Gd-PyMTA ruler the improvement was 3.1-3.4 and for Gd-DOTA-monoamide labeled ubiquitin it was a factor of 1.8. Whereas for the Gd-PyMTA ruler the two setups pump on maximum and observe on maximum gave about the same improvement, for Gd-DOTA-monoamide a significant difference was found. In general the choice of the best set of parameters depends on the D parameter of the Gd(III) complex.

Keywords: Arbitrary waveform generator; Chirp pulses; Double electron–electron resonance; Electron paramagnetic resonance; Gadolinium DEER.

Publication types

Research Support, Non-U.S. Gov't