RIDME Spectroscopy with Gd(III) Centers

Razzaghi, Sahand; Qi, Mian; Nalepa, Anna; Godt, Adelheid; Jeschke, Gunnar; Savitsky, Anton; Yulikov, Maxim

doi:10.1021/jz502129t

Cited by 84 publications

(133 citation statements)

References 42 publications

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“…However, for cases where (i) multi-mode resonators are used and (ii) echo reduction effects at large adiabaticity factors are tolerable, |∆m S | > 1 excitation with chirp pulses may become more prominent. Further data is found in Section 2 of the SI, including a significant narrowing of distance distributions which resembles RIDME data recorded with Gd-ruler 1 3 [5].…”

Section: An Experimental Shortcut To Optimize Sensitivitysupporting

confidence: 54%

“…Note that this offset is determined by the frequency sweep and flip angle of the chirp pulse, as well as by the lineshape of the pumped spins.. For Gdruler 1 3 , the timings were τ 1 = 400 ns, ∆t = 8 ns, and τ 2 = 4.5 µs or 6 µs. For Gd-ruler 1 5 , we used τ 1 = 2 µs, τ 2 = 15 µs and ∆t = 40 ns. For Gd-ruler 1 7 , 1 9 and 1 11 , the timings were τ 1 = 1 µs, ∆t = 100 ns and τ 2 = 18 µs, 20 µs and 22 µs, respectively.…”

Section: Four-pulse Deermentioning

confidence: 99%

“…The majority of experiments to date rely on the four-pulse DEER (double electronelectron resonance) sequence to access distance information between a pair of Gd(III) centers [2]. Modifications of this approach involve the use of non-identical spin labels, in particular a Gd(III) center and a nitroxide [3,4], as well as different experimental schemes, such as relaxation-induced dipolar modulation (RIDME) [5] or continuous-wave EPR [6]. Distance measurements involving Gd spin labels have been successfully demonstrated on a number of systems, including model compounds, peptides, nanoparticles, proteins and DNAs [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21].…”

Section: Introductionmentioning

confidence: 99%

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Gd(III)–Gd(III) distance measurements with chirp pump pulses

Doll

Wili

et al. 2015

Journal of Magnetic Resonance

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The broad EPR spectrum of Gd(III) spin labels restricts the dipolar modulation depth in distance measurements between Gd(III) pairs to a few percent. To overcome this limitation, frequency-swept chirp pulses are utilized as pump pulses in the DEER experiment. Using a model system with 3.4 nm Gd-Gd distance, application of one single chirp pump pulse at Q-band frequencies leads to modulation depths beyond 10%. However, the larger modulation depth is counteracted by a reduction of the absolute echo intensity due to the pump pulse. As supported by spin dynamics simulations, this effect is primarily driven by signal loss to double-quantum coherence and specific to the Gd(III) high spin state of S = 7/2. In order to balance modulation depth and echo intensity for optimum sensitivity, a simple experimental procedure is proposed. An additional improvement by 25% in DEER sensitivity is achieved with two consecutive chirp pump pulses. These pulses pump the Gd(III) spectrum symmetrically around the observation position, therefore mutually compensating for dynamical Bloch-Siegert phase shifts at the observer spins. The improved sensitivity of the DEER data with modulation depths on the order of 20% is due to mitigation of the echo reduction effects by the consecutive pump pulses. In particular, the second pump pulse does not lead to additional signal loss if perfect inversion is assumed. Moreover, the compensation of the dynamical Bloch-Siegert phase prevents signal loss due to spatial dependence of the dynamical phase, which is caused by inhomogeneities in the driving field. The new methodology is combined with pre-polarization techniques to measure long distances up to 8.6 nm, where signal intensity and modulation depth become attenuated by long dipolar evolution windows. In addition, the influence of the zero-field splitting parameters on the echo intensity is studied with simulations. Herein, larger sensitivity is anticipated for Gd(III) complexes with zero-field splitting that is smaller than for the employed Gd-PyMTA complex.

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Section: An Experimental Shortcut To Optimize Sensitivitysupporting

confidence: 54%

Section: Four-pulse Deermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Gd(III)–Gd(III) distance measurements with chirp pump pulses

Doll

Wili

et al. 2015

Journal of Magnetic Resonance

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110

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“…2). RIDME experiments at W band with this type of ruler have been reported previously [31]. The appar-255 ent differences and similarities between RIDME and CIDME are illustrated in Fig.…”

Section: Gd-gd Cidmementioning

confidence: 53%

CIDME: Short distances measured with long chirp pulses

Doll

Godt

et al. 2016

Journal of Magnetic Resonance

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Frequency-swept pulses have recently been introduced as pump pulses into double electron-electron resonance (DEER) experiments. A limitation of this approach is that the pump pulses need to be short in comparison to dipolar evolution periods. The "chirp-induced dipolar modulation enhancement" (CIDME) pulse sequence introduced in this work circumvents this limitation by means of longitudinal storage during the application of one single or two consecutive pump pulses. The resulting six-pulse sequence is closely related to the five-pulse "relaxation-induced dipolar modulation enhancement" (RIDME) pulse sequence: While dipolar modulation in RIDME is due to stochastic spin flips during longitudinal storage, modulation in CIDME is due to the pump pulse during longitudinal storage. Experimentally, CIDME is examined for Gd-Gd and nitroxide-nitroxide distance determination using a high-power Q-band spectrometer. Since longitudinal storage results in a 50% signal loss, comparisons between DEER using short chirp pump pulses of 64 ns duration and CIDME using longer pump pulses are in favor of DEER. While the lower sensitivity restrains the applicability of CIDME for routine distance determination on high-power spectrometers, this result is not to be generalized to spectrometers having lower power and to specialized "non-routine" applications or different types of spin labels. In particular, the advantage of prolonged CIDME pump pulses is demonstrated for experiments at large frequency offset between the pumped and observed spins. At a frequency separation of 1 GHz, a Gd-Gd modulation depth larger than 10% is achieved, where broadening due to dipolar pseudo-secular contributions becomes largely suppressed. Moreover, a CIDME experiment at deliberately reduced power underlines the potential of the new technique for spectrometers with lower power, as often encountered at higher microwave frequencies. With longitudinal storage times T below 10 µs, however, CIDME appears rather susceptible to artifacts. For nitroxide-nitroxide experiments, these currently inhibit a faithful data analysis. To facilitate further developments, the artifacts are characterized experimentally. In addition, effects that are specific to the high spin of S = 7/2 Gd-centers are examined. Herein, population transfer within the observer spin's multiplet due to the pump pulse as well as excitation of dipolar harmonics are discussed.

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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%