Modelling the metal atom positions of the Photosystem II water oxidising complex: a density functional theory appraisal of the 1.9 Å resolution crystal structure.

Density functional theory (DFT) calculations are reported for a set of model compounds intended to represent the structure of the Photosystem II (PSII) water oxidising complex (WOC) as determined by the recent 1.9 Å resolution single crystal X-ray diffraction (XRD) study of Umena et al. In contrast with several other theoretical studies addressing this structure, we find that it is not necessary to invoke photoreduction of the crystalline sample below the S(1)'resting state' in order to rationalise the observed WOC geometry.

The interaction of His337 with the Mn4Ca cluster of photosystem II.

The most recent XRD studies of Photosystem II (PS II) reveal that the His337 residue is sufficiently close to the Mn(4)Ca core of the Water Oxidising Complex (WOC) to engage in H-bonding interactions with the μ(3)-oxo bridge connecting Mn(1), Mn(2) and Mn(3). Such interactions may account for the lengthening of the Mn-Mn distances observed in the most recent and highest resolution (1.9 Å) crystal structure of PS II compared to earlier, lower-resolution (2.

Application of computational chemistry to understanding the structure and mechanism of the Mn catalytic site in photosystem II--a review.

Applications of Density Functional Theory (DFT) computational techniques to studies of the molecular structure and mechanism of the oxygen evolving, water oxidising Mn(4)/Ca catalytic site in Photosystem II are reviewed. We summarise results from the earlier studies (pre 2000) but concentrate mainly on those developments which have occurred since publication of several PS II crystal structures of progressively increasing resolution, starting in 2003. The work of all computational groups actively involved in PS II studies is examined, in the light of direct PS II structural information from X-ray diffraction crystallography and EXAFS on the metals in the catalytic site.

Bridge over troubled water: resolving the competing photosystem II crystal structures.

Density functional theory (DFT) calculations, at the Becke-Perdew/TZP level of theory, were used to investigate a set of CaMn(4)-containing clusters that model the active site of the water-oxidizing complex (WOC) of photosystem II (PSII). Metal-atom positions for three representative isomeric clusters of the formula [CaMn(4)C(9)N(2)O(16)H(10)](+)4 H(2)O are in good agreement with the disparate Mn(4) geometries of the three most recent X-ray crystal structures. Remarkably, interconversion between these three isomeric clusters is found to be facile, resulting from subtle changes in the coordination environment around the CaMn(4) centre.

Extending, and repositioning, a thermochemical ladder: high-level quantum chemical calculations on the sodium cation affinity scale.

High-level ab initio quantum chemical calculations, at the CP-dG2thaw level of theory, are reported for coordination of Na+ to a wide assortment of small organic and inorganic ligands. The ligands range in size from H to C6H6, and include 22 of the ligands for which precise relative sodium ion binding free energies have been determined by recent Fourier transform ion cyclotron resonance and guided ion beam studies. Agreement with the relative experimental values is excellent (+/-1.