Iron spin states

Figure 9.1 CYP catalytic cycle. The sequential two-electron reduction of CYP and the various transient intermediates were first described in the late 1960s [206], The sequence of events that make up the CYP catalytic cycle is shown. The simplified CYP cycle begins with heme iron in the ferric state. In step (i), the substrate (R—H) binds to the enzyme, somewhere nearthe distal region of the heme group and disrupts the water lattice within the enzymes active site [207], The loss of water elicits a change in the heme iron spin state (from low spin to high spin) [208]. Step (ii) involves the transfers of an electron from NADPH via the accessory flavoprotein NADPH-CYP reductase, with the electron flow going from the reductase prosthetic group FAD to FMN to the CYP enzyme [206,209]. The...

Other complexes containing the coordination units FeN2S2 [842] and FeN2S4 [843— 845] are also known. These compounds have due importance in coordination chemistry since they provide a possibility to study the changes of iron spin states in accessible temperature intervals [845]. Moreover, they are permanently used as models of active centers in some iron-containing nonporphyrine metalloenzymes, in particular, nitrylhydrataze [804,846-850]. 

Change in heme iron spin-state shifts this resonance... 

Fig. 1. Iron spin states. Distribution of electrons in the d-orbitals for ferrous (d6), ferric (d5) and ferryl (d4) iron in an octahedral ligand field in the presence of strong (large AE) and weak (small AE) ligands. Spin states (S) for high- and low-spin iron are as indicated.

The most prominent features in NRVS spectra are the strong set of peaks in the middle portion of the spectrum, which are principally from the in-plane motion of iron. At this time, a complete general analysis ofthe in-plane modes is notpossible. However this is probably not a frnal state. A relationship between the frequencies of the in-plane modes, iron spin state, and coordination state can be reasonably expected and is qualitatively observed. The increasing database of NRVS measurements on oriented single crystals of iron porphyrins... 

This hydrogen bonding also impacts Mossbauer spectroscopic properties as shown in Table 3. It should be noted that the use of the B3LYP method has enabled accurate predictions of the Mossbauer quadrupole splittings and isomer shifts in a wide variety of iron proteins and model systems covering all iron spin states and coordination states [8-14,23], with a theory-versus-experiment correlation coefficient R2=0.98 over an experimental range of 8.80 mm/s in 47 systems... 

Resonance Raman data were used to study the change of iron spin state in horseradish peroxidase c - induced by the removal of calcium.238 Ligand modes for spin-state cycling of photosystem II from a cyanobacterium are very similar to those for related systems from spinach.239... 

The peculiar iron spin state in ferricytochrome o from Chromatium has been investigated by Maltempo et al. (44 ) > who studied the EPR spectrum down to 7°K, and measured magnetic susceptibilities between... 

Cyt P450 Heme Iron Spin State Spectral and Electrochemical Properties... 

Krishnan S, Abeykoon A, Schenkman JB, Rusling JF (2009) Control of electrochemical and ferryloxy formation kinetics of cyt P450s in polyion films by heme iron spin state and secondary structure. J Am Chem Soc 131 16215-16224... 

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