Hyperfine Chemical Shifts

S 3 paramagnetic hyperfine chemical shift in ppm for a nucleus i in a complex of a lanthanide j paramagnetic contact shift in ppm for a nucleus i in a complex of a lanthanide j <5 ° paramagnetic pseudo-contact shift in ppm for a... 

Rivera et have used variable temperature NMR hyperfine chemical shifts to probe the electron spin density in a low-spin Fe(III) porphyrinate that models the hydroperoxide intermediate (Felll-OOH) of heme oxygenase. Variable temperature NMR measurements, in conjunction with ENDOR, indicated that the ruffled (dxy) and planar (dxy) spin states are in thermal equilibrium. The authors suggest that this kind of spin-state equilibrium may be important for enzymatic function. The same group used NMR and pulsed ENDOR to characterize the electronic and spin states of C-labeled porphyrin models of the low-spin Fe(III) hydroperoxide intermediate of heme oxygenase. The ferric hydroperoxide intermediate in heme catabolism has also been studied by Caig-nan et using NMR. 

Quantum Calculations. - Mao et aC have carried out density functional calculations of spin density and hyperfine chemical shifts for H, N, and F... 

Bertini et report a detailed study of the magnetic properties of myglobin, in which they determined the axial and orthorhombic terms of the paramagnetic susceptibility tensor using a combination of hyperfine chemical shift measurements and static suscetibility measurements (Evans Method). The determination of the magnetic anisotropy provided a measurement of the residual dipolar couplings and also permitted a separation of the contact and pseudocontact chemical shift contributions of resonances of the Fe(III) ligands. 

Du et have determined the magnitude and orientation of the paramagnetic susceptibility tensor of the cyanomet complex of an 02-avid hemoglobin from the trematode Paramphistomum epiclitum. They used proton hyperfine chemical shifts and paramagnetic relaxation enhancements to probe the chemical bonding at the metal center. 

Vu et al. have carried out a detailed analysis of H, and N hyperfine chemical shifts in two cyanobacterial hemoglobins. This study focuses on the the properties of an unusual cross-link between one of the heme vinyl groups and a histidine located in the C-terminal helix. 

Louro et al have used NMR to characterize a tetrahaem ferricytoch-rome from Shewanella frigidimarina. The heme electronic structure was determined from an analysis of hyperfine chemical shifts of the nuclei bound to the... 

This section describes theoretical work of a fundamental nature that does not clearly belong in one of the sections above. Work focused on a particular chemical system - for example, DFT calculations of hyperfine chemical shifts in porphyrins are described in the Porphyrins section. 

Despite this similarity with chemical shift, the Knight shift is grouped with the electron hyperfine term in (lb) to reflect the fact that both terms arise from the influence of the spin or orbital angular momentum of unpaired electrons. The distinction between the two is that for the electron hyperfine term the electron spin (or hole, as the absence of an electron can be described, e.g., in the case of d9 Cu++) is localized on a paramagnetic defect such as a deep-level transition metal ion. 

In summary, NMR techniques based upon chemical shifts and dipolar or scalar couplings of spin-1/2 nuclei can provide structural information about bonding environments in semiconductor alloys, and more specifically the extent to which substitutions are completely random, partially or fully-ordered, or even bimodal. Semiconductor alloys containing magnetic ions, typically transition metal ions, have also been studied by spin-1/2 NMR here the often-large frequency shifts are due to the electron hyperfine interaction, and so examples of such studies will be discussed in Sect. 3.5. For alloys containing only quadrupolar nuclei as NMR probes, such as many of the III-V compounds, the nuclear quadrupole interaction will play an important and often dominant role, and can be used to investigate alloy disorder (Sect. 3.8). 

Answer NMR characteristics observed in bulk semiconductors such as electron hyperfine effects in dilute magnetic semiconductors [322-324], Knight shifts [234], and chemical shift differences resulting from alloying [325-327] and possibly different polytypes [322, 328] have been observed at the nanoscale. 

Combines sensitivity of EPR and high resolution of NMR to probe ligand super-hyperfine interactions For paramagnetic proteins enhanced chemical shift resolution, contact and dipolar shifts, spin delocalization, magnetic coupling from temperature dependence of shifts Identification of ligands coordinated to a metal centre... 

Results obtained from the alkali iodides on the isomer shift, the NMR chemical shift and its pressure dependence, and dynamic quadrupole coupling are compared. These results are discussed in terms of shielding by the 5p electrons and of Lbwdins technique of symmetrical orthogonalization which takes into account the distortion of the free ion functions by overlap. The recoilless fractions for all the alkali iodides are approximately constant at 80°K. Recent results include hybridization effects inferred from the isomer shifts of the iodates and the periodates, magnetic and electric quadrupole hyperfine splittings, and results obtained from molecular iodine and other iodine compounds. The properties of the 57.6-k.e.v. transition of 1 and the 27.7-k.e.v. transition of 1 are compared. 

Moseley s law spect The law that the square-root of the frequency of an x-ray spectral line belonging to a particular series is proportional to the difference between the atomic number and a constant which depends only on the series. mOz-lez, 10 Mossbauer spectroscopy spect The study of Mossbauer spectra, for example, for nuclear hyperfine structure, chemical shifts, and chemical analysis. mus,bau-3r spek tras ko pe ... 

To determine static properties of the SeO radical in KDP and DKDP, the temperature dependence of the hyperfine interaction between unpaired electron and Se (I = 1/2) nucleus was measured [53]. The hyperfine tensor component A, where the direction is along the c-axis, shows an isotope effect, because its value is higher in DKDP than in KDP. Furthermore, its value shows a jump at Tc for DKDP and a considerable temperature dependence in the PE phase of both crystals, approximated by the relation A (T) = A (0) - B coth(ro/T), where To 570 K for both crystals. It is interesting to note that A, similarly to the As NQR frequency and P isotropic chemical shift, should be constant in the PE phase if the two-state order-disorder mechanism of the corresponding tetrahedron holds. However, while the temperature dependencies of the As NQR frequency and P isotropic chemical shift in the PE phase were explained as originating from a six-state order-disorder mechanism [42] and additional displacive mechanism [46], respectively, here it was assumed that excitation of some extra lattice vibration mode with frequency Tq affects the hyperfine tensor components and causes the temperature dependence of A. ... 

Nevertheless, calculation of such properties as spin-dependent electronic densities near nuclei, hyperfine constants, P,T-parity nonconservation effects, chemical shifts etc. with the help of the two-component pseudospinors smoothed in cores is impossible. We should notice, however, that the above core properties (and the majority of other properties of practical interest which are described by the operators heavily concentrated within inner cores or on nuclei) are mainly determined by electronic densities of the valence and outer core shells near to, or on, nuclei. The valence shells can be open or easily perturbed by external fields, chemical bonding etc., whereas outer core shells are noticeably polarized (relaxed) in contrast to the inner core shells. Therefore, accurate calculation of electronic structure in the valence and outer core region is of primary interest for such properties. 

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