A W-Band Pulsed ENDOR Spectrometer: Setup and Application to Transition Metal Centers

Gromov, Igor; Krymov, Vladimir; Manikandan, P.; Arieli, D.; Goldfarb, Daniella

doi:10.1006/jmre.1999.1762

Cited by 102 publications

(112 citation statements)

References 25 publications

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“…24 FS-ED EPR spectra were recorded using the two-pulse echo sequence (π/2-τ-π-τ-echo) where the echo intensity is registered as a function of the magnetic field. The magnetic field value was determined from the 1 H Larmor frequency obtained from the ENDOR experiments.…”

Section: Methodsmentioning

confidence: 99%

Geometry and Framework Interactions of Zeolite-Encapsulated Copper(II)−Histidine Complexes

et al. 2000

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Abstract:The coordination geometry of zeolite-encapsulated copper(II)-histidine (CuHis) complexes, prepared by ion exchange of the complexes from aqueous solutions into zeolite NaY, was determined by a combination of UV-vis-NIR diffuse reflectance spectroscopy (DRS), X-band EPR, electron-spin-echo envelope modulation (ESEEM), and high field (W-band) pulsed ENDOR techniques. X-band EPR spectroscopy detected two distinct complexes, A and B, which are different from the prevailing Cu(II) bis-His complex in the exchange solution (pH 7.3 with a His:Cu(II) ratio of 5:1). Moreover, the relative amount of complex B was found to increase with increasing Cu(II) concentration. The EPR parameters of complex A are g ⊥ ) 2.054, g | ) 2.31, and A | ) 15.8 mT, whereas those of complex B are g ⊥ ) 2.068, g | ) 2.25, A | ) 18.3 mT, and A ⊥ ( 14 Ν) ∼ 1.3 mT. The presence of the 14 N superhyperfine splitting shows that in complex B three nitrogens are coordinated to the Cu(II). Furthermore, DRS exhibits a shift of the d-d absorption band of Cu(II) from 15 200 cm -1 in complex A to 15 900 cm -1 in complex B, indicating an increasing ligand field strength in the latter. The coordination of the imino nitrogen of the imidazole group was detected in the two complexes via the ESEEM frequencies of the remote nitrogen. In contrast, only complex A exhibited 27 Al modulation, which indicates that the Cu(II) binds to zeolite framework oxygens. 2 H and 1 H W-band ENDOR measurements on samples where the exchangeable protons were replaced with 2 H, and using specifically labeled histidine (His-R-d--d 2 ), lead to the unambiguous determination of the coordination configuration of the two complexes. Complex A is a monoHis complex where both the amino and imino nitrogens are coordinated and the other equatorial ligands are provided by a zeolite oxygen and a water molecule. Complex B is a bis-His complex, which is situated in the center of the supercage, and all equatorial coordination sites are provided by the His molecules. These are amino and imino nitrogens of one His molecule and the imino nitrogen and carboxylate oxygen of the second His molecule. Complex A can be converted into complex B by stirring the zeolite in a high pH solution, whereas complex B is converted into complex A by using a low pH solution, thus indicating that complex A is stabilized by the presence of intrazeolitic protons. On the basis of the structure of the complexes, the dependence of their relative amounts on the pH and Cu(II) concentration in the exchange solution, the His: Cu(II) ratio in the zeolite, the amount of exchanged Na(I) ions, and the steric constraints imposed by the zeolite framework, a model for the ion exchange processes and the intrazeolite reactions leading to the formation of the two complexes is presented.

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Section: Methodsmentioning

confidence: 99%

Geometry and Framework Interactions of Zeolite-Encapsulated Copper(II)−Histidine Complexes

et al. 2000

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“…Therefore, pulsed EPR applications preferably make use of a single-mode resonator. At 95 GHz, an incident power of approximately 100 mW is necessary for a p/2 pulse of 50 ns (cavity Q = 2000) [28]. At 180 GHz, this is 20 mW (Q = 1500) [38].…”

Section: Single-mode Resonators (Te 011 )mentioning

confidence: 99%

“…The Donetsk Physical-Technical Institute (Ukraine) constructed several pulsed EPR bridges operating at 95 and 130 GHz with output powers of 200 and 50 mW, respectively. In combination with a single-mode resonator, these bridges enable excellent performance in pulsed EPR applications including pulsed ENDOR [28].…”

Section: Impatt Oscillatormentioning

confidence: 99%

“…A convenient way to adjust the coupling is by rotating the resonator around the waveguide coupling to the iris hole in the cylinder wall. This mode allows a large iris hole, which facilitates the scaling up to higher frequencies [20,28,82]. A specific challenge is to combine the resonator with an ENDOR coil enabling pulse ENDOR applications.…”

Section: Single-mode Resonators (Te 011 )mentioning

confidence: 99%

“…The technicians from the Donetsk PhysicalTechnical Institute (Ukraine), who were instrumental in the development of the mm-wave bridges (95-150 GHz) of the Lebedev group, introduced pulsed mmwave bridges at 95 and 130 GHz using high-power impact avalanche and transit time (IMPATT) amplifiers (200 mW at 95 GHz and 50 mW at 130 GHz). These instruments were produced on a commercial basis and found their way to several laboratories in the world [28][29][30][31][32][33]. The increasing interest in higher-frequency EPR spectrometers ([200 GHz) has stimulated the systematic application of quasioptical techniques in mm-wave propagation and resonator coupling and was initiated by Smith et al [34] and Freed et al [18,35].…”

Section: Introductionmentioning

confidence: 99%

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High-Frequency EPR Instrumentation

Reijerse¹

2009

Appl Magn Reson

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An overview of the most recent developments in high-frequency highfield electron paramagnetic resonance (EPR) instrumentation is given. In particular, the practical choices concerning sources, detectors, resonators, propagation systems as well as magnet technology are discussed in the light of various possible applications. Examples of particular homodyne and heterodyne quasi-optic EPR systems illustrate the potential for future developments in EPR technology.

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Studies of Fe(III) incorporated into AlPO4-20 by X- and W-band EPR spectroscopies

et al. 1999

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A W-Band Pulsed ENDOR Spectrometer: Setup and Application to Transition Metal Centers

Cited by 102 publications

References 25 publications

Geometry and Framework Interactions of Zeolite-Encapsulated Copper(II)−Histidine Complexes

Geometry and Framework Interactions of Zeolite-Encapsulated Copper(II)−Histidine Complexes

High-Frequency EPR Instrumentation

Studies of Fe(III) incorporated into AlPO4-20 by X- and W-band EPR spectroscopies

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