Superhyperfine

Transannular interaction via the electron-delocalization mechanism was found, but lessened by 10-15% for the ligand superhyperfine splitting and 30-35% for the hyperfine splitting (62) in the epr spectrum. The crystal structure of [VOS2CNEt2)2] shows that the molecular core has the expected C2V symmetry [V-0 = 159.1(4), V-S = 138.7(2)-241.0(2) pm] (63). Magnetic and spectral data provided evidence for a tetragonal, pyramidal structure (VII) for these complexes. Like many other coordinatively unsaturated, metal... 

Combines sensitivity of EPR and high resolution of NMR to probe ligand superhyperfine 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... 

An alternative model (Venable 1967) proposes that the main cause of inhomogeneous broadening is unresolved superhyperfine interactions and, therefore, that the linewidth expression should be equivalent to the Equation 5.12 for the angular dependence of first-order hyperfine splitting ... 

The superhyperfine splittings are sufficiently small to ignore second-order effects at X-band, and for adducts of the nitrone compounds splitting from the nitrone-N and the beta-H are the only resolved hyperfine interactions, thus affording the extremely simple resonance condition (cf. Equation 5.10)... 

The main application of double resonance is the resolution of hyperfine and particularly superhyperfine interactions that are not extractable from regular EPR spectra because they are lost in the inhomogeneous line. The biological relevance is in otherwise unavailable detailed information on the electronic structure and the coordination of active sites and their interaction with reactants, such as enzyme substrates. To be well prepared, check off the items in the following list. 

Antholine, W.E., Hanna, P.M., and McMillan, D.R. 1993. Low frequency EPR of Pseudomonas aeruginosa azurin analysis of ligand superhyperfine structure from a type 1 copper site. Biophysical Journal 64 267-272. 

Besides the hyperfine constants for the muonium impurity itself, one can also investigate the so-called superhyperfine interaction for the neighboring 29Si atoms. These values have also been accurately measured (Kiefl et al., 1988) with level-crossing resonance.For the anisotropic parameters, it is customary to compare b with Aj,ree, which is an average of r 3 determined for the valence p-orbital. The results are given in Table II. Both... 

The superhyperfine interaction is observed for metal complexes in cases where the metal ligands have a nuclear moment. For instance, the nitrosyl (NO) complexes of iron(II) heme proteins have two inequivalent axial nitrogen ligands. The 14N(/ = 1) NO couples strongly to the unpaired electron, yielding a widely split triplet with each component of equal intensity and separated by 2.1 mT. The second... 

In contrast to the narrow signal of H(I), which exhibits a single Lorentzian profile, the feature observed for H(IV) and H(V) was more complex (Fig. 23 lb) with splitting into five lines indicating a superhyperfine structure (line denoted A in Fig. 23 2). This phenomenon is due to the hyperfine interaction between localized spin and two neighboring nitrogen nuclei (nuclear spin... 

Halogen-donor Ligands. The a- and p-modifications of LiVF have been obtained by reaction of LiF and VF3 (3 1) and quenching or slowly cooling the products, respectively." Hyperfme and superhyperfine interactions of V " ions in MFj crystals (M = Ca. Sr, or Cd) have been studied at 4.2 K. " ... 

F superhyperfine couplings in the axially symmetric frozen solution spectrum [ReNF4] showing two pairs of sextets in parallel and perpendicular part. 

Oxovanadium(IV) complexes with dithiophosphate ligands have been extensively examined <8,121.161,252,386) x typical ESR spectrum is shown in Fig. 7. In addition to the eight vanadium 1=112 hyperfine lines phosphorus (/ = 1/2) superhyperfine splitting is also observed. The phosphorus superhyper-fine splitting can be considered a bit unusual since the phosphorus is located about 3 A or more away from the metal ion. P and As superhyperfine splitting has been observed in the ESR spectra of ill-defined vanadium phosphine 388) and arsine 389) complexes but in those cases, presumably, direct V-P and V—As interactions occur. ESR parameters have been tabulated for a large number of dithiophosphate 121,252) dithiophosphinate 121.252) complexes. Evaluation 3i) of the fractional 3s character of unpaired electron in dithiophosphate complexes yielded a value of 1.35%. The vanadyl(IV) complexes possess approximate C2V symmetry. The unpaired d electron resides... 

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