Complete Determination of Nitrogen Quadrupole and Hyperfine Tensors in an Oxovanadium Complex by Simultaneous Fitting of Multifrequency ESEEM Powder Spectra
✍ Scribed by E.J. Reijerse; A.M. Tyryshkin; S.A. Dikanov
- Publisher
- Elsevier Science
- Year
- 1998
- Tongue
- English
- Weight
- 464 KB
- Volume
- 131
- Category
- Article
- ISSN
- 1090-7807
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✦ Synopsis
One-dimensional C-and X-band as well as two-dimensional Xare governed by a significant isotropic hfi (5-7 MHz) leadband ESEEM experiments were performed on the complex oxoing to dominating double-quantum features. In addition, at bis(2-methylquinolin-8-olato) vanadium(IV) in frozen solution. A the orientation-selection positions close to the ''single-crys-14 N ESEEM simulation strategy based on initial first-and secondtal-like'' conditions, the lines from single-quantum transiorder perturbation analysis of peak positions in orientationally tions as well as the combination peaks in two-pulse spectra selected ESEEM spectra is presented. The constraint parameters are usually well pronounced. Dikanov et al. ( 16) derived extracted enable one to reduce the number of free fitting paramethe second-order analytical expressions for this set of experiters for each nitrogen from 10 to 4. These are the a, b resp. the mental features unlimited by any restrictions on the relative f, u Euler angles of the NQI and the HFI tensor defined in the orientation of nitrogen hyperfine and quadrupole tensors and coordinate system of the axial g tensor. The local symmetry of the the applied magnetic field. The application of these exprescomplex allows one to reduce the number of free parameters to two angles only. Subsequently, a grid search in the remaining sions to the analysis of the frequency positions of the Euler space produced the starting parameters for the final fit of ESEEM signals provides reliable starting values or conthe 14 N hyperfine and quadrupole tensors. The anisotropic nitrogen straints for hyperfine and quadrupole parameters which sighyperfine interaction tensor was found to be strongly nonaxial nificantly simplify the final fitting of the experimental data. (0.06, 0.51, 00.57) MHz with the components significantly smaller As a result of such analysis, the determination of the hyperthan the isotropic hyperfine constant 06.18 MHz. In contrast, the fine and quadrupole tensors of the coordinating histidine quadrupole tensor with K Å 0.58 MHz is close to axial (h Å 0.13).
nitrogen in VO 2/ -substituted D-xylose isomerase was re-These tensors share the principal axis normal to the ligand plane ported (16). These tensors have provided a comprehensive (as imposed by the local symmetry). The axes in the ligand plane magnetic resonance picture of the electronic and geometrical are, however, rotated 50Њ with respect to each other. The orientation of the quadrupole tensor axes correlate within 10Њ with the structure of nitrogen coordination in an oxovanadium comorientation of the ligand plane following from the X-ray structure. plex.