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- Title
High-sensitivity Gd<sup>3+</sup>-Gd<sup>3+</sup> EPR distance measurements that eliminate artefacts seen at short distances.
- Authors
EL Mkami, Hassane; Hunter, Robert I.; Cruickshank, Paul A. S.; Taylor, Michael J.; Lovett, Janet E.; Feintuch, Akiva; Mian Qi; Godt, Adelheid; Smith, Graham M.
- Abstract
Gadolinium complexes are attracting increasing attention as spin labels for EPR dipolar distance measurements in biomolecules and particularly for in-cell measurements. It has been shown that flip-flop transitions within the central transition of the high-spin Gd3+ ion can introduce artefacts in dipolar distance measurements, particularly when measuring distances less than 3 nm. Previous work has shown some reduction of these artefacts through increasing the frequency separation between the two frequencies required for the double electron-electron resonance (DEER) experiment. Here we use a high-power (1 kW), wideband, non-resonant system operating at 94 GHz to evaluate DEER measurement protocols using two stiff Gd(III) rulers, consisting of two bis-Gd3+-PyMTA complexes, with separations of 2.1 nm and 6.0 nm, respectively. We show that by avoiding the |-1/2}→|1/2} central transition completely, and placing both the pump and the observer pulses on either side of the central transition, we can now observe apparently artefact-free spectra and narrow distance distributions, even for a Gd-Gd distance of 2.1 nm. Importantly we still maintain excellent signal-to-noise ratio and relatively high modulation depths. These results have implications for in-cell EPR measurements at naturally occurring biomolecule concentrations.
- Subjects
GADOLINIUM compounds; ELECTRON paramagnetic resonance; BIOMOLECULES; SIGNAL-to-noise ratio; PARAMAGNETIC ions
- Publication
Magnetic Resonance, 2020, Vol 1, Issue 2, p301
- ISSN
2699-0016
- Publication type
Article
- DOI
10.5194/mr-1-301-2020