Amplitudes of Superhyperfine Frequencies Displayed in the Electron-Spin-Echo Envelope

Mims, W. B.

doi:10.1103/physrevb.6.3543

Cited by 208 publications

(126 citation statements)

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“…Nuclear quadrupole coupling terms are treated later. Equation 2 shows the normalized S = 112, I = 1 threepulse echo modulation for Gd+3, which has an almost isotropic g value and negligible quadrupole coupling (14,15). The nearly isotropic g value of Gd+3 was confirmed by our simulations of EPR spectra of Gd+3 in a glassy matrix (17).…”

supporting

confidence: 67%

Solvate structures in water‐methanol solutions of MRI contrast agents: Electron spin echo envelope modulation in gadolinium chelates

Clarkson

Hwang

Belford

1993

Magnetic Resonance in Med

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Electron Spin Echo Envelope Modulation (ESEEM) data are reported for three gadolinium (III) chelates, Gd-EDTA, Gd-DTPA, and Gd-TTHA, in frozen D2O/CH3OD glasses. This series includes Gd-DTPA, an MRI contrast agent that is in clinical use. Three-pulse electron spin echo modulation patterns can be modeled to yield geometrical information; e.g., distances and numbers of Gd+3-OD interactions. Interpreted by a spherical shell model, the data for Gd-TTHA are accounted for by Gd+3 surrounded by seven deuterons at an effective distance of 3.9 A. We attribute these deuterons to second-coordination sphere solvent molecules, since it is likely that Gd+3 is fully coordinated by a TTHA ligand. For analysis of ESEEM from Gd-EDTA and Gd-DTPA, the second-sphere structures of Gd-EDTA, Gd-DTPA, and Gd-TTHA are assumed equivalent. 2H-ESEEM from inner-sphere solvent molecules gives the effective distance between deuterons and Gd+3 to be approximately 2.7 A for the inner-sphere water in both EDTA and DTPA complexes. The results of simulations also give the isotropic hyperfine and quadrupole coupling constants for solvent deuterium in these systems. Possible sources of error in the determination of r and q by this method are discussed.

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supporting

confidence: 67%

Solvate structures in water‐methanol solutions of MRI contrast agents: Electron spin echo envelope modulation in gadolinium chelates

Clarkson

Hwang

Belford

1993

Magnetic Resonance in Med

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“…The ESEEM spectra were obtained from the sum of individual ESEEM waveforms recorded with τ in the range of 0.16-0.73 (steps of 0.03 µs) to eliminate the τ dependence of the modulation amplitudes. 31 Both spectra (Figure 3b) exhibit three lines, at 0.7, 1.4, and 4.0 MHz, which are typical for the remote 14 N of the imidazole ring. 16,32 At X-band, this nitrogen obeys the cancellation condition where in one of the electron spin manifolds the nuclear Zeeman interaction and the hyperfine interaction cancel each other, resulting in a zero effective field.…”

Section: Resultsmentioning

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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“…Measurements were carried out at 20 K and s values were varied from 120 to 440 ns in order to avoid suppression effects. 34 Using hyperfine sublevel correlation spectroscopy (HYSCORE) the nuclear coherence within one electronic manifold is transferred by an additional MW pulse into the corresponding nuclear coherence within the other electronic manifold (Fig. 2C).…”

Section: Epr Spectroscopymentioning

confidence: 99%

Elucidating mechanisms in haemcopperoxidases: The high-affinity Q_Hbinding site in quinol oxidase as studied by DONUT-HYSCOREspectroscopy and density functional theory

et al. 2011

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Amplitudes of Superhyperfine Frequencies Displayed in the Electron-Spin-Echo Envelope

Cited by 208 publications

References 1 publication

Solvate structures in water‐methanol solutions of MRI contrast agents: Electron spin echo envelope modulation in gadolinium chelates

Solvate structures in water‐methanol solutions of MRI contrast agents: Electron spin echo envelope modulation in gadolinium chelates

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

Elucidating mechanisms in haemcopperoxidases: The high-affinity Q_Hbinding site in quinol oxidase as studied by DONUT-HYSCOREspectroscopy and density functional theory

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Amplitudes of Superhyperfine Frequencies Displayed in the Electron-Spin-Echo Envelope

Cited by 208 publications

References 1 publication

Solvate structures in water‐methanol solutions of MRI contrast agents: Electron spin echo envelope modulation in gadolinium chelates

Solvate structures in water‐methanol solutions of MRI contrast agents: Electron spin echo envelope modulation in gadolinium chelates

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

Elucidating mechanisms in haemcopperoxidases: The high-affinity QHbinding site in quinol oxidase as studied by DONUT-HYSCOREspectroscopy and density functional theory

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Elucidating mechanisms in haemcopperoxidases: The high-affinity Q_Hbinding site in quinol oxidase as studied by DONUT-HYSCOREspectroscopy and density functional theory