Diamagnetic states

The Mosshauer data performed on the as-isolated D. vulgaris [Fe] hydrogenase are in agreement with the EPR data, and further support the presence of two ferredoxin-type [4Fe-4S] clusters and that the H-cluster is in the diamagnetic state in the as-purified enzyme (169). 

The active site in the aerobic, inactive D. vulgaris enzyme shows no EPR signals. The FTIR spectrum indicates the presence of a bridging CO, in addition to the end-on bound CN/CO pair to each iron atom (Fig. 7.2, trace A). We presently assume that both Fe atoms in the bimetallic site are low-spin ferric and that their S = 1/2 systems are anti-ferromagnetically coupled to a diamagnetic state. 

Eurther decrease in redox potential, -200 mV, only affects the [3Fe-4S] cluster properties (one electron reduced in the [3Ee-4S] state). The EPR spectrum now shows a g = 12 feature due to a S = 2 spin system. Mossbauer data clearly illustrates this point, ruling out the possibility of a [3Ee-4S] to [4Ee-4S] cluster interconversion. The two [4Ee-4S] clusters remain in the diamagnetic state, indicating that they have a lower redox potential. 

The FeMo cofactor (or M center) in the MoFe-proteinis in the native paramagnetic M state. Reduction of the MoFe-protein by the Fe-protein results in the reduction of FeMo-co from the M state to the M state at a potential estimated to be less than —0.465 V (NHE). The electron paramagnetic resonance (EPR) silent M state is only transiently produced during catalysis, and relaxes to the M state when catalysis stops. The intimate consequences of the M state reduction are not precisely known. A more oxidized diamagnetic state may also be generated (M ) at —0.042 V but its biological relevance is unclear [9]. 

In one sample, the crossover from the metallic (Pauli paramagnetic) region to the diamagnetic state occurred at 32 K. The diamagnetism measured was rather weak, on the order of 1% Meissner fraction, as compared to a pure superconductor (-1/47T, the full Meissner effect). 

For octahedral complexes only in the d6 case does equilibrium occur between a diamagnetic state and a paramagnetic T state. In the other three cases one of the isomers is in a paramagnetic A or E ground state [Eqs. (2 5)]. 

These experiments showed clearly that n states evolve into the quasi-Landau resonances. In higher resolution experiments, Gay et a/.18 and Castro et al.19 showed that it was in fact the highest energy diamagnetic states which evolved into... 

Diamagnetic States Ion Triples to Alkali Metal Anions... 

Oxyhemoglobin the heme iron atoms are in the low-spin ferrous, diamagnetic state Carbon monoxyhemoglobin the heme iron atoms are in the low-spin ferrous, diamagnetic state Methemoglobin the heme iron atoms are in the high-spin ferric state with five unpaired electrons per heme iron... 

Since the zero-order wave function of a diamagnetic state is a linear combination of the degenerate basis wave functions and the diamagnetic interaction allows for extension of dipole selection rules to Al = 1, 3, the equation for the coefficient q is modified to read (we consider the lower state to be non-degenerate, with l = m ) ... 

The transverse PRE r2 is the difference between the R2 rates in the paramagnetic and diamagnetic states of the system and can be calculated from peak intensities in R2 experiments at two time points without the need for relaxation rate fitting81 ... 

An important feature of the results obtained is the recapture of the electrons released from traps at Ti 30-60 K and Tz 110-150 K by the paramagnetic centers that form the f-signal of EPR (Fig. 6, curves 1). Only when these centers finish their work does the transformation of the lithium paramagnetic centers into the diamagnetic state begin (Tz 150-180 K,... 

When the MoFe protein is isolated in the presence of excess dithionite, its P clnster is in an S = 4, diamagnetic state (designated 4,49,50 (jjg pN g g... 

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