Dead-Time Free Measurement of Dipole–Dipole Interactions between Electron Spins

Abstract

A four-pulse version of the pulse double electron-electron resonance (DEER) experiment is presented, which is designed for the determination of interradical distances on a nanoscopic length-scale. With the new pulse sequence electron-electron couplings can be studied without dead-time artifacts, so that even broad distributions of electron-electron distances can be characterized. A version of the experiment that uses a pulse train in the detection period exhibits improved signal-to-noise ratio. Tests on two nitroxide biradicals with known length indicate that the accessible range of distances extends from about 1.5 to 8 nm. The four-pulse DEER spectra of an ionic spin probe in an ionomer exhibit features due to probe molecules situated both on the same and on different ion clusters. The former feature provides information on the cluster size and is inaccessible with previous methods.

Encoded loop-lanthanide-binding tags for long-range distance measurements in proteins by NMR and EPR spectroscopy

“…Pulsed EPR data were recorded on an ELEXSYS E580 EPR spectrometer (Bruker) equipped with a PELDOR unit (E580-400U, Bruker), a continuous-flow helium cryostat (CF935, Oxford Instruments), and a temperature control system (ITC 502, Oxford Instruments). Experiments were performed at Q-band frequencies (33.7 GHz) using an ELEXSYS SuperQ-FT accessory unit and a Bruker AmpQ 10 W amplifier with a Bruker EN5107D2 cavity at 10 K. For PELDOR experiments, the dead-time free four-pulse sequence with phasecycled p/2-pulse was used (Pannier et al 2000). Pulse lengths were optimized to 16 ns (p/2 and p) for the observer pulses and 8 ns (p) for the pump pulse.…”

Accurate Extraction of Nanometer Distances in Multimers by Pulse EPR

“…The 4‐pulse PELDOR experiment is mostly used for distance measurements 8. Briefly, one set of spins (A‐spins) is probed by a detection pulse sequence while the dipolar coupling is selectively introduced by inverting a second set of spins (B‐spins) with a pump pulse (usually placed on the most intense feature of the spectrum).…”

Measuring Spin⋅⋅⋅Spin Interactions between Heterospins in a Hybrid [2]Rotaxane

“…Recently,A rdavan et al have shown using double electronelectron resonance (DEER) spectroscopy that the interaction between electron spins in {Cr 7 Ni}r ings can be controlled to fall within the range needed for two qubit gates.[3] These studies were performed on dimers of {Cr 7 Ni}rings [4] where the S = 1/2 spins in each half are identical.Systems containing different spins also have great potential for QIP as there is then the possibility of manipulating each spin separately.T his underpins the g-engineering idea proposed by Takui and co-workers for organic radicals [5] and work employing heterometallic lanthanide dimers.[6] Large differences in g-values could also be used as am eans to implement entangling two qubit gates.[7] Quantifying weak interactions between very different spins is challenging.I n cases where the interaction can easily be measured, for example by magnetometry or continuous-wave (CW) electron paramagnetic resonance (EPR) spectroscopy, [8] the interaction will be too large to permit implementation of both one-and two-qubit gates in the same molecule.[3] CW EPR spectroscopy can still be au seful tool to investigate dipolar interactions;byobserving the line broadening of aN triplet in at wo-qubit structure,Z hou et al showed the existence of ad ipolar interaction that they could estimate in conjunction with spin density calculations.[9] On the other hand, DEER spectroscopy, [10] while ap owerful tool to measure weak interactions by directly manipulating two weakly interacting spins with specific microwave pulses,i s limited as the bandwidth of the microwave source must encompass the resonant frequency of both electron spins.Here we report at wo-qubit assembly comprising an organic radical within the thread of ah ybrid [2]rotaxane containing a{Cr 7 Ni}ring:this is aheterospin system where the constituent spins possess vastly different g-values.T oquantify the weak interaction between the spins we use "Relaxation Induced Dipolar Modulation" (RIDME) spectroscopy, [11] which has been developed in structural biology to measure distances between dissimilar spins. [12] To make the [2]rotaxane an organic thread was synthesized containing as econdary amine and terminating in an aldehyde (see the Supporting Information for details).…”

“…[9] On the other hand, DEER spectroscopy, [10] while ap owerful tool to measure weak interactions by directly manipulating two weakly interacting spins with specific microwave pulses,i s limited as the bandwidth of the microwave source must encompass the resonant frequency of both electron spins.…”

“…[3] CW EPR spectroscopy can still be au seful tool to investigate dipolar interactions;byobserving the line broadening of aN triplet in at wo-qubit structure,Z hou et al showed the existence of ad ipolar interaction that they could estimate in conjunction with spin density calculations. [9] On the other hand, DEER spectroscopy, [10] while ap owerful tool to measure weak interactions by directly manipulating two weakly interacting spins with specific microwave pulses,i s limited as the bandwidth of the microwave source must encompass the resonant frequency of both electron spins.…”