A pulsed EPR method to determine distances between paramagnetic centers with strong spectral anisotropy and radicals: The dead-time free RIDME sequence

Averaging of nuclear modulation artefacts in RIDME experiments

“…[14,24,25] The second approach, which offers nearly infinite effective bandwidth of the coupling partner, utilizes the longitudinal Relaxation Induced Dipolar Modulation En-30 hancement (RIDME) technique. [26][27][28][29][30][31][32][33] Being a single frequency technique, RIDME imposes low requirements on the resonator profile and measurement setup. On the downside, the RIDME time traces have typically faster decaying intermolecular background, as compared to DEER, and, for high-spin 35 metal centres, also contain contributions of dipolar frequency overtones.…”

“…The currently used approaches to avoid ESEEM arte-to-noise ratio (SNR), since they are either based on the use of very soft microwave pulses or require trace by trace division. [27,29,30] The latter approach reduces signal-to-noise ratio by at least a factor of two, with a factor √ 2 coming from the requirement of measuring a reference trace that does not add 55 to the dipolar modulation and another factor of √ 2 at the signal maximum and more at later time from dividing two noisy traces.…”

“…The pulse sequence of the dead time free RIDME experiment [27] is shown in Figure 80 1(a) and the echo detected (ED) EPR spectrum of the Gd(III)-PyMTA complex is shown in Figure 1(b) with the RIDME detection position marked by an arrow. Detailed experimental setting and sample preparation descriptions can be found in the Supporting Information.…”

“…Figure 1: (a) RIDME pulse sequence, PE stands for the primary spin echo, and RE for the detected RIDME echo (refocused virtual echo in reference [27]), (b) EDEPR spectrum of the Gd-ruler (3.4 nm) at 34.5 GHz. The magnetic field position for detection of the RIDME sequence is marked by an arrow, (c), (d) Structural formulae of the studied model compounds.…”

“…There are two time points in the RIDME sequence where all contributions to the detected RIDME echo (refocused virtual echo in [27]) assume a rather simple dependence on the electron spin operators. First, at the primary echo time point 2d 1 all contributions that later form the RIDME echo refocus along the y-direction.…”