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

Abstract

Abstract. Double electron–electron resonance (DEER) is a pulse electron paramagnetic resonance (EPR) technique that measures distances between paramagnetic centres. It utilizes a four-pulse sequence based on the refocused Hahn spin echo. The echo decays with increasing pulse sequence length 2(τ1+τ2), where τ1 and τ2 are the two time delays. In DEER, the value of τ2 is determined by the longest inter-spin distance that needs to be resolved, and τ1 is adjusted to maximize the echo amplitude and, thus, sensitivity. We show experimentally that, for typical spin centres (nitroxyl, trityl, and Gd(III)) diluted in frozen protonated solvents, the largest refocused echo amplitude for a given τ2 is obtained neither at very short τ1 (which minimizes the pulse sequence length) nor at τ1=τ2 (which maximizes dynamic decoupling for a given total sequence length) but rather at τ1 values smaller than τ2. Large-scale spin dynamics simulations based on the coupled cluster expansion (CCE), including the electron spin and several hundred neighbouring protons, reproduce the experimentally observed behaviour almost quantitatively. They show that electron spin dephasing is driven by solvent protons via the flip-flop coupling among themselves and their hyperfine couplings to the electron spin.

Evolution of CPEB4 Dynamics Across its Liquid–Liquid Phase Separation Transition

“…This observation is also supported by the much faster echo decay, where spin–spin interactions dominate the phase relaxation ( Figure S8B ). 57 The similar echo-decay rate and close DEER decays in the non-LLPS and LLPS states suggest the presence of small assemblies within the droplets, and it is their local concentration which determines the echo and the DEER decays.…”

dHis-troying Barriers: Deuteration Provides a Pathway to Increase Sensitivity and Accessible Distances for Cu2+ Labels

“…The hydrogen–deuteration exchange halftimes for solvent-exposed amide protons have been shown to occur in seconds at a physiological pH . Additionally, solvent atoms are densely packed around the spin center, which provides a significant contribution to signal dephasing …”

“…38 Additionally, solvent atoms are densely packed around the spin center, which provides a significant contribution to signal dephasing. 39 To overcome relaxation induced by solvent protons, we incorporated combinations of d 8 -glycerol and D 2 O with dGB1. Protein deuteration leads to a substantial increase in the size of the echo at large dipolar evolution times, with the signal sustaining until 32 μs (cf.…”

Milliwatt three- and four-pulse double electron electron resonance for protein structure determination

“…The 3-pulse and 4-pulse DEER time traces are characterized by having the same background decay function, indicating that the influence of spin diffusion effects is negligible. [18][19][20] To experimentally revive the 3-pulse data from the remaining dead time, we used the DEER-Stitch method introduced by Lovett et al 43 The idea of this method is to measure a short 4-pulse DEER time trace alongside the desired 3-pulse time trace using the same experimental parameters. The length of the 4-pulse sequence should just be long enough to cover the dead time and to provide a region of overlap between the two signals.…”

“…We want to stress that this is a greatly simplified model since it neither takes into account ESEEM effects that can strongly modulate the observer echo amplitude, nor the effects of detecting on a Hahn echo as it is the case in 3-pulse DEER with respect to detecting on a refocused echo as it is the case in the 4-pulse DEER experiment. [18][19][20] The realizable gains will be sample-dependent and more moderate. Some exemplary values providing a maxium estimation for the signal gain are given in Table S1 (ESI †).…”