Ligand ENDOR of Metal Complexes in Powders
01 May 1970-Journal of Chemical Physics (American Institute of Physics)-Vol. 52, Iss: 9, pp 4633-4643
TL;DR: In this paper, the electron-nuclear double-resonance (ENDOR) spectra are obtained from molecules in a single orientation with respect to the magnetic field and powder-type endor spectra from molecules of many orientations.
Abstract: Magnetically dilute crystalline powders of the following metal complex systems have been prepared by coprecipitation: copper salicylaldoxime in palladium salicylaldoxime, copper dimethylglyoxime in nickel dimethylglyoxime, copper picolinate in phthalic acid and also in zinc picolinate, copper 2‐methylpicolinate in zinc 2‐methylpicolinate, copper quinaldinate in zinc quinaldinate, copper 8‐hydroxyquinolinate in phthalimide and also in zinc 8‐hydroxyquinolinate, and silver picolinate in phthalic acid and also in zinc picolinate. These samples have been investigated with electron–nuclear double‐resonance (ENDOR) spectroscopy. At some settings of the magnetic field, single‐crystal‐type ENDOR spectra are obtained which arise substantially from molecules in a single orientation with respect to the magnetic field. At other settings of the field, powder‐type ENDOR spectra are found which arise from molecules in many orientations. In either case the spectra are simpler and easier to interpret than the EPR powder s...
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01 Jan 1996
TL;DR: In this article, the photoacoustic method in photosynthesis - Monitoring and analysis of Phenomena which Lead to Pressure Changes Following Light Excitation S.J. Hoff and P.M. Small.
Abstract: Preface. Part One: Optical Methods. 1. Developments in Classical Optical Spectroscopy J. Amesz. 2. Linear and Circular Dichroism G. Garab. 3. Fluorescence K. Sauer, M. Debreczeny. 4. Ultrafast Spectroscopy of Photosynthetic Systems R. Jimenez, G.R. Fleming. 5. Data Analysis of Time-Resolved Measurements A.R. Holzwarth. 6. Photosynthetic Thermoluminescence as a Simple Probe of Photosystem II Electron Transport Y. Inoue. 7. Accumulated Photon Echo Measurements of Excited State Dynamics in Pigment-Protein Complexes T.J. Aartsma, R.J.W. Louwe, P. Schellenberg. 8. Spectral Hole Burning: Methods and Applications to Photosynthesis N. Raja, S. Reddy, G.J. Small. 9. Infrared and Fourier-Transform Infrared Spectroscopy W. Mantele. 10. Resonance Raman Studies in Photosynthesis - Chlorophyll and Carotenoid Molecules B. Robert. 11. Stark Spectroscopy of Photosynthetic Systems S.G. Boxer. 12. The Photoacoustic Method in Photosynthesis - Monitoring and Analysis of Phenomena which Lead to Pressure Changes Following Light Excitation S. Malkin. Part Two: Magnetic Resonance. 13. Magnetic Resonance: an Introduction A.J. Hoff. 14. Time-Resolved Electron Paramagnetic Resonance Spectroscopy - Principles and Applications H. Levanon. 15. Electron Spin Echo Methods in Photosynthesis Research R.D. Britt. 16. ENDOR Spectroscopy W. Lubitz, F. Lendzian. 17. Optically Detected Magnetic Resonance (ODMR) of Triplet States in Photosynthesis A.J. Hoff. 18. MagicAngle Spinning Nuclear Magnetic Resonance of Photosynthetic Components H.J.M. de Groot. Part Three: Structure and Oxygen. 19. Structure Determination of Proteins by X-Ray Diffraction M. Schiffer. 20. Electron Microscopy E.J. Boekema, M. Roegner. 21. X-Ray Absorption Spectroscopy:Determination of Transition Metal Site Structures in Photosynthesis V.K. Yachandra, M.P. Klein. 22. Moessbauer Spectroscopy P.G. Debrunner. 23. Characterization of Photosynthetic Supramolecular Assemblies Using Small Angle Neutron Scattering D.M. Tiede, P. Thiyagarajan. 24. Measurements of Photosynthetic Oxygen Evolution H.J. van Gorkom, P. Gast.
329 citations
TL;DR: In this article, a double electron-electron resonance (DEER) spin-echo technique was applied to measure the electron−electron dipolar spectrum of a frozen toluene solution of the biradical, 2,6bis[(((2,2,5, 5tetramethyl]-1−oxypyrrolin‐3]-yl)carbonyl)oxy)]−anthracene.
Abstract: A DEER (double electron–electron resonance) spin–echo technique was applied to measure the electron–electron dipolar spectrum of a frozen toluene solution of the biradical, 2,6‐bis[(((2,2,5, 5‐tetramethyl‐1‐oxypyrrolin‐3‐yl)carbonyl)oxy)]‐anthracene. Modulation of the DEER spin–echo envelope was observed and identified as originating from the dipolar coupling between the two nitroxide spins of the biradical. Fourier transformation of the modulated components of the echo envelope yielded a dipolar spectrum from which a spin–pair separation of 19.73±0.14 A was calculated. Constraints on the relative orientation of the two nitroxide spin moieties were obtained by analysis of the effect of the microwave pulse orientational selectivity on the DEER modulation amplitudes. Molecular models of the studied compound exhibit structures that correspond well with the structural information deduced by DEER spectroscopy.
230 citations
TL;DR: A critical review is given of this widely applied dosimetric method based on the (presumed) correlation between the intensity or amplitude of some of the radiation-induced signals with the dose absorbed in the enamel.
208 citations
Cites methods from "Ligand ENDOR of Metal Complexes in ..."
...this respect is the application of the “orientation selection principle” (Rist and Hyde, 1970)....
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...Essential in this respect is the application of the “orientation selection principle” (Rist and Hyde, 1970)....
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TL;DR: The structure deduced here for the PDO cluster is generally applicable to the full class of Rieske-type centers and the bonding parameters of the coordinated nitrogens are fully consistent with those of an spn hybrid on a histidyl nitrogen coordinated to Fe.
Abstract: We have performed ENDOR spectroscopy at microwave frequencies of 9 and 35 GHz at 2 K on the reduced Rieske-type (2Fe-2S) cluster of phthalate dioxygenase (PDO) from Pseudomonas cepacia. Four samples have been examined: (1) 14N (natural abundance); (2) uniformly 15N labeled; (3) (15N)histidine in a 14N background; (4) (14N)histidine in a 15N background. These studies establish unambiguously that two of the ligands to the Rieske (2Fe-2S) center are nitrogens from histidine residues. This contrasts with classical ferredoxin-type (2Fe-2S) centers in which all ligation is by sulfur of cysteine residues. Analysis of the polycrystalline ENDOR patterns has permitted us to determine for each nitrogen ligand the principal values of the hyperfine tensor and its orientation with respect to the g tensor, as well as the 14N quadrupole coupling tensor. The combination of these results with earlier Moessbauer and resonance Raman studies supports a model for the reduced cluster with both histidyl ligands bound to the ferrous ion of the spin-coupled (Fe2+ (S = 2), Fe3+ (S = 5/2)) pair. The analyses of 15N hyperfine and 14N quadrupole coupling tensors indicate that the geometry of ligation at Fe2+ is approximately tetrahedral, with the (Fe)2(N)2 plane corresponding to the g1-g3 plane, andmore » that the planes of the histidyl imidazoles lie near that plane, although they could not both lie in the plane. The bonding parameters of the coordinated nitrogens are fully consistent with those of an spn hybrid on a histidyl nitrogen coordinated to Fe. Differences in 14N ENDOR line width provide evidence for different mobilities of the two imidazoles when the protein is in fluid solution. We conclude that the structure deduced here for the PDO cluster is generally applicable to the full class of Rieske-type centers.« less
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TL;DR: In this paper, a linear relation between the hyperfine splitting due to proton N, aN, and the unpaired spin density on carbon atom N, ρN, n = QρN is derived under very general conditions.
Abstract: Indirect proton hyperfine interactions in π‐electron radicals are first discussed in terms of a hypothetical CH fragment which holds one unpaired π electron and two σ‐CH bonding electrons. Molecular orbital theory and valence bond theory yield almost identical results for the unpaired electron density at the proton due to exchange coupling between the π electron and the σ electrons. The unrestricted Hartree‐Fock approximation leads to qualitatively similar results. The unpaired electron spin density at the proton tends to be antiparallel to the average spin of the π electron, and this leads to a negative proton hyperfine coupling constant.The theory of indirect proton hyperfine interaction in the CH fragment is generalized to the case of polyatomic π‐electron radical systems; e.g., large planar aromatic radicals. In making this generalization there is introduced an unpaired π‐electron spin density operator, ρN, where N refers to carbon atom N. Expectation values of the spin density operator ρN are called ``spin densities,'' ρN, and can be positive or negative. In the simple one‐electron molecular orbital approximation a π‐electron radical always has a positive or zero spin density at carbon atom N, 0≤ρN≤1. In certain π‐electron radical systems; e.g., odd‐alternate hydrocarbon radicals, the spin densities at certain (unstarred) carbon atoms are negative when the effects of π—π configuration interaction are included in the π‐electron wave function.The previously proposed linear relation between the hyperfine splitting due to proton N, aN, and the unpaired spin density on carbon atom N, ρN, aN=QρN is derived under very general conditions. Two basic approximations are necessary in the derivation of this linear relation. First, it is necessary that σ—π exchange interaction can be treated as a first‐order perturbation in π‐electron systems. Second, it is necessary that the energy of the triplet antibonding state of the C–H bond be much larger than the excitation energies of certain doublet and quartet states of the π electrons. This derivation of the above linear relation makes no restrictive assumptions regarding the degree of π—π or σ—σ configuration interaction. The validity of the above approximations is discussed and illustrated by highly simplified calculations of the proton hyperfine splittings in the allyl radical, assuming the π—π configuration interaction—and hence the negative spin density on the central carbon atom—to be small.Isotropic hyperfine interactions in molecules in liquid solution can also arise from spin‐orbital interaction effects, and it is shown that these effects are negligible for proton hyperfine interactions in aromatic radicals.
782 citations
TL;DR: The ground-state wave function of the antimony, phosphorus, and arsenic impurities in silicon has been investigated by means of the electron nuclear double resonance (ENDOR) method as discussed by the authors.
Abstract: The ground-state wave function of the antimony, phosphorus, and arsenic impurities in silicon has been investigated by means of the electron nuclear double resonance (ENDOR) method By this method the hyperfine interactions of the donor electron with the ${\mathrm{Si}}^{29}$ nuclei situated at different lattice sites were obtained The isotropic part of the hyperfine interaction agreed with the theory of Kohn and Luttinger to better than 50% From a comparison of the experimental results with their theory a value for the conduction band minimum in silicon of $\frac{{k}_{0}}{{k}_{max}}=085\ifmmode\pm\else\textpm\fi{}003$ was obtained So far no satisfactory theory exists to account quantitatively for the observed anisotropic part of the hyperfine interactionThe observed line shape agreed with the shape predicted by summing up the individual hyperfine interactions which are the cause of the broadening The behavior of an inhomogeneously broadened line observed under adiabatic fast passage conditions is discussed in an appendix The electronic $g$-values were measured with respect to the free carriers in a degenerate $n$-type silicon sample The $g$-value of the free carriers was found to be 199875\ifmmode\pm\else\textpm\fi{}000010 The deviations of the donor $g$-values from the above value is several parts in ${10}^{4}$ and increases monotonically with increasing ionization energy of the donorsBesides the shallow donors Sb, P, and As, several other centers were investigated, but in considerably less detail They include the chemical impurities Bi, Li, Fe, centers associated with the surface of the sample and with the heat treatment of silicon The influence of substitutional germanium atoms on the resonance line in phosphorus-doped silicon has also been investigated
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TL;DR: Only for you today!
Abstract: Only for you today! Discover your favourite magnetic resonance in biological systems book right here by downloading and getting the soft file of the book. This is not your time to traditionally go to the book stores to buy a book. Here, varieties of book collections are available to download. One of them is this magnetic resonance in biological systems as your preferred book. Getting this book b on-line in this site can be realized now by visiting the link page to download. It will be easy. Why should be here?
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TL;DR: In this article, a nuclear double resonance has been performed on six free radicals in solution with polar and nonpolar solvents, and both neutral and ionic radicals investigated.
Abstract: Electron nuclear double resonance has been performed on six free radicals in solution. Polar and nonpolar solvents were employed, and both neutral and ionic radicals investigated. The instrumentation is described in detail. Features of the instrument include: pulsed nuclear radio‐frequency magnetic fields, rf fields as high as 40 G in the rotating frame, and provision to observe changes in the EPR spectrum caused by nuclear resonance with the ordinary EPR spectrum subtracted (ENDOR‐induced EPR). ENDOR mechanisms and adjustment of experimental conditions to achieve optimum signal intensity are discussed. It is established that successful ENDOR experiments can be performed on a large number of free radicals in solution, resulting in improved resolution, simplification of spectra and more accurate hyperfine splittings.
164 citations