Optimising broadband pulses for DEER depends on concentration and distance range of interest

Abstract

Abstract. EPR distance determination in the nanometre region has become an important tool for studying the structure and interaction of macromolecules. Arbitrary waveform generators (AWGs), which have recently become commercially available for EPR spectrometers, have the potential to increase the sensitivity of the most common technique, double electron–electron resonance (DEER, also called PELDOR), as they allow the generation of broadband pulses. There are several families of broadband pulses, which are different in general pulse shape and the parameters that define them. Here, we compare the most common broadband pulses. When broadband pulses lead to a larger modulation depth, they also increase the background decay of the DEER trace. Depending on the dipolar evolution time, this can significantly increase the noise level towards the end of the form factor and limit the potential increase in the modulation-to-noise ratio (MNR). We found asymmetric hyperbolic secant (HS{1,6}) pulses to perform best for short DEER traces, leading to a MNR improvement of up to 86 % compared to rectangular pulses. For longer traces we found symmetric hyperbolic secant (HS{1,1}) pulses to perform best; however, the increase compared to rectangular pulses goes down to 43 %.

Chirped ordered pulses for ultra-broadband ESR spectroscopy

“…2,[26][27][28] Pulses for broadband inversion have been reported, such as in dipolar spectroscopy with the double electron-electron resonance (DEER) pump pulse. [29][30][31][32] The use of swept-frequency pulses for broadband excitation has also been explored, but to a lesser extent. 18,[33][34][35][36][37][38][39][40][41] Here, we present an implementation of the CHORUS (CHirped ORdered pulses for Ultra-broadband Spectroscopy) sequence 22,24 for ultra-broadband excitation in ESR spectroscopy.…”

Towards fully optimised and automated ESR spectroscopy

“…However, the choice of appropriate shape parameters is not trivial and has been the subject of extensive investigations. 23,24 Here, the goal is to adjust the selectivity of a hyperbolic secant (HS) pulse by finding a suitable truncation factor b (see eqn (S1) and (S2), ESI †). Although numerical simulations can be used to study the effects of the pulse, they cannot easily take into account important hardware effects on the shaped pulse and, in this case, did not suggest a suitable value for b (see Fig.…”