Artefact suppression in 5-pulse double electron electron resonance for distance distribution measurements

Abstract

A 5-pulse version of the Double Electron Electron Resonance (DEER) experiment with Carr-Purcell delays and an additional pump pulse has been shown to significantly extend the experimentally accessible distance range in cases where nuclear spin diffusion dominates electron spin phase memory loss [Borbat et al., J. Phys. Chem. Lett., 2013, 4, 170]. We show that the sequence also prolongs coherence decay for spin labels in or near lipid bilayers, where this decay is mono-exponential. Compared to 4-pulse DEER, 5-pulse DEER suffers from additional artefacts that stem from pulse imperfection and excitation band overlap. Only some of these artefacts can be suppressed by phase cycling and the remaining ones have hindered widespread utilization of the method. Here, we report previously unknown additional artefact contributions stemming from overlap between the excitation bands of the microwave pulses that introduce additional dipolar evolution pathways. Experimental conditions are analyzed in detail that suppress these as well as the already known artefacts. Such suppression results in data that contain at most the partial excitation artefact, which can be deliberately shifted in time by a change in pulse timing without affecting the wanted contribution.

The decay of the refocused Hahn echo in double electron–electron resonance (DEER) experiments

“…However, this concentration reduction leads to a loss in absolute signal intensity and may significantly prolong the experiment runtime, and therefore, there is an optimal concentration for the best SNR (Jeschke and Polyhach, 2007). Another mechanism that strongly contributes to dephasing is nuclear spin diffusion, which is driven by magnetic nuclei that are coupled to the electron spin and among themselves (Brown, 1979;Canarie et al, 2020;Huber et al, 2001;Lenz et al, 2017;Milov et al, 1972;Mims, 1972;Salikhov and Tsvetkov, 1979;Zecevic et al, 1998). The dephasing by this mechanism is enhanced in particular by nuclei with a large gyromagnetic ratio, such as protons.…”

DeerLab: A comprehensive toolbox for analyzing dipolar EPR spectroscopy data

“…Despite their clear dipolar origin, these are regarded as undesirable "artifacts": the "2+1 artifact" in 4-pulse DEER (Jeschke, 2012;Teucher and Bordignon, 2018), and "artifacts" or "residues" in 5-pulse and 7-pulse DEER (Borbat et al, 2013;Spindler et al, 2015;Breitgoff et al, 2017b, a;Doll and Jeschke, 2017;Milikisiyants et al, 2018). Several experimental and processing approaches have been published that aim to remove these contributions from the total signal to recover the idealized dipolar evolution function (Borbat et al, 2013;Spindler et al, 2015;Teucher and Bordignon, 2018;Breitgoff et al, 2017b, a). These approaches introduce further experimental or theoretical complexity.…”

DEER and RIDME Measurements of the Nitroxide-Spin Labelled Copper-Bound Amine Oxidase Homodimer from Arthrobacter Globiformis

“…In analysing the data acquired by the DEER experiment on the same sample, the DeerStitch method was required due to the phase memory time of the Cu(II) being too short to measure the long distances we aim to observe [31]. It should be noted that other DEER sequences, including five-and seven-pulse, are able to produce the same result of a longer phase memory time, but that these methods work significantly better with shaped pulses [63,64]. Therefore, due to the simplicity of DeerStitch method, with the available rectangular pulses, it was employed here.…”