scholarly journals pH-dependent forms of the ferryl haem in myoglobin peroxide analysed by variable-temperature magnetic circular dichroism

1989 ◽  
Vol 261 (2) ◽  
pp. 515-522 ◽  
Author(s):  
N Foote ◽  
P M A Gadsby ◽  
C Greenwood ◽  
A J Thomson
Keyword(s):  
Circular Dichroism ◽  
Magnetic Circular Dichroism ◽  
Variable Temperature ◽  
Zero Field ◽  
Zero Field Splitting ◽  
Zero Field Splitting Parameter ◽  
Varied Temperature ◽  
Splitting Parameter ◽  
Catalytic Cycles ◽  
Circular Dichroïsm

The reaction product of myoglobin and H2O2 exists in two different forms according to the external pH. Varied-temperature magnetic-circular dichroism (m.c.d.) spectroscopy demonstrates that both contain the oxyferryl ion Fe(IV) = O. Alkaline myoglobin peroxide has often been used as a model for oxidized intermediates in the catalytic cycles of haem-containing peroxidases, but absorption and m.c.d. spectra show that the acid form is much more closely related to species such as horeradish peroxidase Compound II. The differences are tentatively ascribed to ionization of the proximal histidine ligand in alkaline myoglobin peroxide. It is also shown that the m.c.d. method allows an estimate of the zero-field splitting parameter of both forms, values of D = 28.0 +/- 3 cm-1 and 35.0 +/- 5 cm-1 being obtained for the alkaline and acid forms respectively.

A variable temperature EPR study of Mn2+-doped NH4Cl0.9I0.1 single crystal at 170GHz: Zero-field splitting parameter and its absolute sign

2005 ◽  
Vol 174 (2) ◽  
pp. 265-269 ◽  
Author(s):  
Sushil K. Misra ◽  
Serguei I. Andronenko ◽  
Prem Chand ◽  
Keith A. Earle ◽  
Sergei V. Paschenko ◽  
...  
Keyword(s):  
Single Crystal ◽  
Variable Temperature ◽  
Zero Field ◽  
Zero Field Splitting ◽  
Field Splitting ◽  
Zero Field Splitting Parameter ◽  
Splitting Parameter

Absorption and magnetic circular dichroism spectra of nitrogen homologues of magnesium and zinc phthalocyanine

1993 ◽  
Vol 71 (11) ◽  
pp. 1898-1909 ◽  
Author(s):  
Edward A. Ough ◽  
Martin J. Stillman ◽  
Katherine A.M. Creber
Keyword(s):  
Circular Dichroism ◽  
Magnetic Circular Dichroism ◽  
Electron System ◽  
Zinc Phthalocyanine ◽  
Zero Field ◽  
Molecular Symmetry ◽  
Zero Field Splitting ◽  
Benzene Rings ◽  
Circular Dichroïsm ◽  
Magnetic Circular Dichroism Spectra

Absorption and magnetic circular dichroism (MCD) spectra are reported for the metallophthalocyanine-N-isologs: magnesium-3,4-pyridinoporphrazine (MgPcN4(−2)), zinc-3,4-pyridinoporphyrazine (ZnPcN4(−2)), and zinc-3,4-pyridazinoporphyrazine (ZnPcN8(−2)). Band deconvolution calculations, which couple both the absorption and the MCD spectra, are reported for each complex. The presence of the peripherally fused pyridine rings in MgPN4(−2) and ZnPcN4(−2) reduces the molecular symmetry and splits the degenerate Q band into its x and y components with zero field splitting parameters (ΔQxy) of 224 and 279 cm−1, respectively. Band fitting results for ZnPcN8(−2) show that with the fused pyridazine rings the degeneracy in the 1Eg excited state is retained and the MCD envelope in the region of the Q00 transition can be described by an MCD A term. Comparison of the fitted band energies with the results reported for ZnPc(−2) (T. Nyokong, Z. Gasyna, and M.J. Stillman. Inorg. Chem. 26, 1087 (1987)) and MgPc(−2) (E.A. Ough, T. Nyokong, K.A.M. Creber, and M.J. Stillman. Inorg. Chem. 27, 2725 (1988)) shows that as the number of nitrogens substituted increases from 0 to 8, the Q band blue shifts from 671 nm in ZnPc(−2) to 664 nm in ZnPcN4(−2) (midpoint between the x and y components) to 654 nm in ZnPcN8(−2) and from 672 nm in MgPc(−2) to 666 nm in MgPcN4(−2) (midpoint). These results demonstrate that chemical modification (symmetric and asymmetric) of the peripherally fused benzene rings influences both the energy and the symmetry of the states that form the inner 18-π-electron system.

Modulation of the coordination environment: a convenient approach to tailor magnetic anisotropy in seven coordinate Co(ii) complexes

2016 ◽  
Vol 52 (4) ◽  
pp. 753-756 ◽  
Author(s):  
Mamon Dey ◽  
Snigdha Dutta ◽  
Bipul Sarma ◽  
Ramesh Ch. Deka ◽  
Nayanmoni Gogoi
Keyword(s):  
Magnetic Anisotropy ◽  
Zero Field ◽  
Zero Field Splitting ◽  
Field Splitting ◽  
Coordination Environment ◽  
Zero Field Splitting Parameter ◽  
Convenient Approach ◽  
Splitting Parameter ◽  
Remarkable Deviation

Subtle modulation of the coordination environment in seven coordinate Co(ii) complexes leads to a remarkable deviation in the axial zero field splitting parameter (D) in a predictable fashion.

Correlation of Zero Field Splittings and Site Distortions V. Mn2+ in Cs2Zn3S4

1983 ◽  
Vol 38 (2) ◽  
pp. 149-153 ◽  
Author(s):  
M. Heming ◽  
G. Lehmann
Keyword(s):  
Fine Structure ◽  
Hyperfine Splitting ◽  
Site Symmetry ◽  
Zero Field ◽  
Structure Parameters ◽  
Zero Field Splitting ◽  
Zero Field Splitting Parameter ◽  
Free Ion ◽  
Splitting Parameter ◽  
Epr Signal

Abstract In platelets of Cs2Zn3S4 with about 4% of the Zn substituted by Mn two nonequivalent centers of isolated Mn2+ were observed in addition to a broad EPR signal near g = 2 which is assigned to clusters of interconnected MnS4 units. The fine structure and hyperfine structure parameters for the single-ion centers (all in units of 1CT 4 cm -1) areb02 = -318.3 ± 3; b22 = -210.3 ± 2; Ay = -62.7; Az = -63.6 ± 0.8;b02 = -890 ± 18; b22 = -743 ± 36; Ay = -60.6; Az = - 61.4 ± 0.8;for centers I and II, resp. Center II arises from Zn sites of C 2 site symmetry while for center I assignment to either one of two sites with D2 site symmetry is possible. The larger hyperfine splitting constants as well as the superposition analysis favor the larger sites which are not occupied by Zn, but are partly occupied in the analogous Mn (and Co) compounds. Superposition analysis yields the same value of + 0.12 ± 0.02 cm-1 for the intrinsic zero field splitting parameter b̄2 of the bridging MnS4 units in both sites. gz is significantly higher than the free ion value indicating a higher degree of covalency than in Cds and CdGa2S4.

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