Oral 23rd International Society of Magnetic Resonance Conference 2023

Spin polarisation in Gd(III) complexes by arbitrary waveform generated excitation pulses for high sensitivity pulsed EPR measurements away from the central transition (#87)

Ciarán Rogers 1 , Alexey Bogdanov 2 , Manas Seal 2 , Matthew Thornton 1 , Louise Natrajan 1 , Daniella Goldfarb 2 , Alice Bowen 1
  1. Department of Chemistry, Photon Science Institute and the National Research Facility for Electron Paramagnetic Resonance, The University of Manchester, Manchester, United Kingdom
  2. Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot, Israel

Half-Integer High Spin (HIHS) systems, such as Gd(III) complexes, with zero-field splitting (ZFS) parameters below 1 GHz are generally dominated by the central EPR transition (CT). Accordingly, most pulsed EPR experiments are performed at this position for maximum sensitivity.[1] However, it may be desirable to detect away from the CT in such systems. Following on from previous work,[2,3] we describe arbitrary waveform generated and bandwidth compensated frequency swept WURST amplitude polarisation pulses for transferring spin population from the CT (and other transitions) of Gd(III) to the neighbouring high spin transitions at Q- and W-band.

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One useful application is the use of pre-polarising pulses for the enhanced sensitivity of Mims ENDOR experiments detecting away from the CT. This was shown to give an enhancement factor greater than 2 in model Gd(III) complexes at Q- and W-band.[4] Experimental considerations in pulse design, the limitations of pre-polarisation detecting on different Gd(III) complexes and potential future applications will be discussed. As higher temperatures are generally easier to achieve and maintain on standard EPR set-ups, polarisation transfer from the CT can be seen as a means to mimic the gain in the Boltzmann distribution of the lower lying energy levels by thermal polarisation at very high magnetic fields and low temperatures.

  1. Goldfarb, D., Phys. Chem. Chem. Phys., 2014, 16, 9685-9699
  2. Kaminker, I. et al., Phys. Chem. Chem. Phys., 2009, 11, 6799-6806
  3. Doll, A. et al., Phys. Chem. Chem. Phys., 2015, 17, 7334-7344
  4. Rogers, C. J. et al., J. Mag. Res., 2023, 351, 107447