Electron dipole–dipole interaction in ESEEM of nitroxide biradicals

Кулик, Л. В.; Dzuba, Sergei A.; Grigoryev, I.A.; Tsvetkov, Yu. D.

doi:10.1016/s0009-2614(01)00721-7

Cited by 193 publications

(198 citation statements)

References 18 publications

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“…To remove the ambiguity, a RIDME experiment was performed. 11 In this experiment, we observed a refocused stimulated ESE signal of the HE-TPP radical, while the longitudinal relaxation of the [4Fe-4S] 1+ center (instead of pumping at a different microwave frequency) served the purpose of modifying the local magnetic field for the radical spin. Since the [4Fe-4S] 1+ center at any orientation is subject to longitudinal relaxation, 12 there is no orientational selectivity in the RIDME experiment.…”

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confidence: 98%

“…In this work, two such techniques were used, electron-electron double resonance (ELDOR) 10 and relaxation-induced dipolar modulation enhancement (RIDME). 11 In the pulsed ELDOR experiment, the primary electron spin-echo (ESE) signal of the [4Fe-4S] 1+ cluster was observed, while the pumping microwave pulse was in resonance with the HE-TPP radical. The Fourier transform (FT) spectrum of the time-domain ELDOR trace exhibits a prominent peak at 1.5 MHz and a smaller feature at 2.7 MHz (trace 1 in Figure 2).…”

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Pulsed Electron Paramagnetic Resonance Experiments Identify the Paramagnetic Intermediates in the Pyruvate Ferredoxin Oxidoreductase Catalytic Cycle

et al. 2006

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Pyruvate ferredoxin oxidoreductase (PFOR) 1 is a thiamine pyrophosphate (TPP)-dependent enzyme that catalyzes the anaerobic oxidation of pyruvate (with CoA) to acetyl-CoA, CO 2 , and two electrons that are transferred to ferredoxin (eq 1). 2 In this paper, the PFOR electrontransfer mechanism is examined. Early steps in the catalytic cycle follow the Breslow 3 mechanism of TPP activation. After deprotonation, the carbanion at C-2 of TPP reacts with pyruvate to form 2-lactyl-TPP, which decarboxylates to generate CO 2 and the resonant enamine/carbanion intermediate, hydroxyethylidene-TPP (HE-TPP). The fate of this intermediate differs among the TPP-dependent enzymes. In PFOR, oxidation of the intermediate is linked to reduction of an external electron acceptor, for example, the clostridial ferredoxin, which contains two [4Fe-4S] clusters.(1)After formation of HE-TPP, the next step in the PFOR mechanism is one-electron transfer from HE-TPP to one of three [4Fe-4S] 2+ clusters, which generates a paramagnetic [4Fe-4S] 1+ cluster and an HE-TPP radical. 4 This paramagnetic intermediate forms at a rate constant of 140 s −1 at 10 °C (~3000 s −1 at the growth temperature of 55 °C). 4 On the basis of the PFOR structure, 5 cluster A, located only 9.5 Å from the thiazole sulfur of HE-TPP, is one of three [4Fe-4S] clusters that are separated by 10-12 Å (Figure 1). 6 Since biological electron transfer is facile whenever the donor and acceptor are within ~15 Å, clusters A (proximal), B (medial), and C (distal, ~4 Å from the surface) are ideally positioned to sequentially transfer electrons to the surface and the external ferredoxin. Cluster A is logically the first to be reduced, since clusters B and C are >20 Å from the radical center on HE-TPP. In the pulsed ELDOR experiment, the primary electron spin-echo (ESE) signal of the [4Fe-4S] 1+ cluster was observed, while the pumping microwave pulse was in resonance with the HE-TPP radical. The Fourier transform (FT) spectrum of the time-domain ELDOR trace exhibits a prominent peak at 1.5 MHz and a smaller feature at 2.7 MHz (trace 1 in Figure 2). Although this spectral shape is reasonably close to that expected in a situation of complete orientational disorder, some orientational selectivity caused by the g-anisotropy of the [4Fe-4S] 1+ center cannot be excluded. To remove the ambiguity, a RIDME experiment was performed. 11 In this experiment, we observed a refocused stimulated ESE signal of the HE-TPP radical, while the longitudinal relaxation of the [4Fe-4S] 1+ center (instead of pumping at a different microwave frequency) served the purpose of modifying the local magnetic field for the radical spin. Since the [4Fe-4S] 1+ center at any orientation is subject to longitudinal relaxation, 12 there is no orientational selectivity in the RIDME experiment.The RIDME experiment was performed at 13 and 4.2 K. At 13 K, the cluster relaxes much more rapidly than at 4.2 K. The difference between the two stimulated ESE spectra gave the RIDME spectrum shown by trace 2 in Figure 2. The only reli...

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Pulsed Electron Paramagnetic Resonance Experiments Identify the Paramagnetic Intermediates in the Pyruvate Ferredoxin Oxidoreductase Catalytic Cycle

et al. 2006

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“…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).…”

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

et al. 2017

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Use of molecular electron spins as qubits for quantum computing will depend on the ability to produce molecules with weak but measurable interactions between the qubits.H ere we demonstrate use of pulsed EPR spectroscopy to measure the interaction between two inequivalent spins in ahybrid rotaxane molecule.Molecular electron spins are potential qubits for quantum information processing (QIP).[1] Much recent work has been dedicated to showing that the phase memory times of S = 1/2 molecules can be controlled, and extended to the point where multiple spin manipulations will be possible.[2] One of the key next steps is to study the interactions between such spins. 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).

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“…[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.…”

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confidence: 99%