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The overall manganese oxidization states of the oxygen-evolving complex (OEC) in the [S.sub.0] and [S.sub.2] states are determined for methanol containing spinach photosystem II (PSII) membrane fragments. The analysis has shown that the [Mn.sub.4][O.sub.x]Ca cluster has taken part in the unique water splitting chemistry through the structural changes, of which one can be located within the cluster.

Electron paramagnetic resonance (EPR) study on Co(II)corrins Cob(II)ester(1+) and base-off B12r(2+) provides the first direct evidence for axial solvent ligation in polar solvents. EPR forms an excellent tool to analyze subtle changes in the electronic structure of Co(super II)-corrin systems, especially when they are supported by density functional computations.

The simulations of both strongly and weakly coupled protons, along with the known copper hyperfine couplings, were used to estimate and compare the spin density distribution in the various CuA centers. The largest sulfur spin density was found in M160T9, and the lowest was found in purpAz.

(super 55)MN pulse ENDOR spectra for the So and S2 states at Q-band frequency is reported. Numerical analysis of the spectra shows that all four Mn ions are magnetically coupled, allows a refinement of the hyperfine interaction (HFI) parameters for the S2 state and provides the first reliable HFI tensors for the S0 state.

Research into the impact of axial ligand mutation on the Cu(sub A) site in the recombinant water soluble fragment of subunit II of Thermus thermophilus cytochrome c oxidase ba3 is presented. It is concluded that the axial ligand has a small but significant impact on the spin distribution in the Cu(sub A) centre, reflecting on the ground-state wave function.

The heart of the oxygen-evolving complex (OEC) of photosystem II is a Mn4OxCa cluster that cycles through five different oxidation states (S0 to S4) during the light-driven water-splitting reaction cycle. In this study we interpret the recently obtained 55Mn hyperfine coupling constants of the S0 and S2 states of the OEC [Kulik et al. J. Am. Chem. Soc. 2005, 127, 2392-2393] on the basis of Y-shaped spin-coupling schemes with up to four nonzero exchange coupling constants, J. This analysis rules out the presence of one or more Mn(IIions in So in methanol (3%) containing samples and thereby establishes that the oxidation states of the manganese ions in S0 and S2 are, at 4 K1 Mn4(III, III, III, IV) and Mn4(III, IV, IV, IV), respectively. By applying a ‘structure filter’ that is based on the recently reported single-crystal EXAFS data on the Mn4OxCa cluster [Yano et al. Science 2006, 314, 821-825] we (i) show that this new structural model is fully consistent with EPR and 55Mn-ENDOR data, (ii) assign the Mn oxidation states to the individual Mn ions, and (iii) propose that the known shortening of one 2.85 Å Mn-Mn distance in S0 to 2.75 Å in S1 [Robblee et al. J. Am. Chem. Soc. 2002, 124, 7459-7471] corresponds to a deprotonation of aμ-hydroxo bridge between MnA and MnB, i.e., between the outer Mn and its neighboring Mn of the μ3-oxo bridged moiety of the cluster. We summarize our results in a molecular model for the S0 → S1 and S1 → S2 transitions. [ABSTRACT FROM AUTHOR]

Examines the electron-mediating copper centers in proteins. Structure of the nearest ligands of copper sites; Electron-nuclear double resonance spectra of the proteins; Relationship between the structure of the copper sites and the electron transfer characteristics.

The article states that powered by light-induced charge separations that generate oxidizing equivalents of about +1.3 Volt, photosystem II (PSII) has the unique capability to oxidize water to molecular oxygen. A manganese complex housed in a special protein environment that also controls proton movements and the access of water catalyzes water splitting. This functional unit of PSII is referred to as the oxygen-evolving complex. PSII created the aerobic atmosphere on earth and may serve as a model for technical approaches to split water by sunlight, which is a prerequisite for a sustainable hydrogen economy. In this article, the authors report manganese pulse ENDOR spectra for the oxidation states at Q-band frequency.

The heart of the oxygen-evolving complex (OEC) of photosystem II is a Mn4OxCa cluster that cycles through five different oxidation states (S0 to S4) during the light-driven water-splitting reaction cycle. In this study we interpret the recently obtained 55Mn hyperfine coupling constants of the S0 and S2 states of the OEC [Kulik et al. J. Am. Chem. Soc. 2005, 127, 2392-2393] on the basis of Y-shaped spin-coupling schemes with up to four nonzero exchange coupling constants, J. This analysis rules out the presence of one or more Mn(II) ions in S0 in methanol (3%) containing samples and thereby establishes that the oxidation states of the manganese ions in S0 and S2 are, at 4 K, Mn4(III, III, III, IV) and Mn4(III, IV, IV, IV), respectively. By applying a "structure filter" that is based on the recently reported single-crystal EXAFS data on the Mn4OxCa cluster [Yano et al. Science 2006, 314, 821-825] we (i) show that this new structural model is fully consistent with EPR and 55Mn-ENDOR data, (ii) assign the Mn oxidation states to the individual Mn ions, and (iii) propose that the known shortening of one 2.85 A Mn-Mn distance in S0 to 2.75 A in S1 [Robblee et al. J. Am. Chem. Soc. 2002, 124, 7459-7471] corresponds to a deprotonation of a mu-hydroxo bridge between MnA and MnB, i.e., between the outer Mn and its neighboring Mn of the mu3-oxo bridged moiety of the cluster. We summarize our results in a molecular model for the S0 --> S1 and S1 --> S2 transitions.

Detailed information on the structure of cobalt(II) corrinates is of interest in the context of studies on the coenzyme B(12) catalyzed enzymatic reactions, where cob(II)alamin has been identified as a reaction intermediate. Cob(II)ester (heptamethyl cobyrinate perchlorate) is found to be soluble in both polar and nonpolar solvents and is therefore very suitable to study solvent effects on Co(II) corrinates. In the literature, Co(II) corrinates in solution are often addressed as four-coordinated Co(II) corrins. However, using a combination of continuous-wave (CW) and pulse electron paramagnetic resonance (EPR) and pulse ENDOR (electron nuclear double resonance) at different microwave frequencies we clearly prove axial ligation for Cob(II)ester and the base-off form of cob(II)alamin (B(12r)) in different solvents. This goal is achieved by the analysis of the g values, and the hyperfine couplings of cobalt, some corrin nitrogens and hydrogens, and solvent protons. These parameters are shown to be very sensitive to changes in the solvent ligation. Density functional computations (DFT) facilitate largely the interpretation of the EPR data. In the CW-EPR spectrum of Cob(II)ester in methanol, a second component appears below 100 K. Different cooling experiments suggest that this observation is related to the phase transition of methanol from the alpha-phase to the glassy state. A detailed analysis of the EPR parameters indicates that this transition induces a change from a five-coordinated (above 100 K) to a six-coordinated (below 100 K) Co(II) corrin. In a CH(3)OH:H(2)O mixture the phase-transition properties alter and only the five-coordinated form is detected for Cob(II)ester and for base-off B(12r) at all temperatures. Our study thus shows that the characteristics of the solvent can have a large influence on the structure of Co(II) corrinates and that comparison with the protein-embedded cofactor requires some caution. Finally, the spectral similarities between Cob(II)ester and base-off B(12r) prove the analogies in their electronic structure.