Characterization of the Mn Oxidation States in Photosystem II by Kβ X-ray Fluorescence Spectroscopy

Abstract

The nature of the Mn oxidation states involved in photosynthetic oxygen evolution has remained controversial, despite intense study by X-ray absorption and electron paramagnetic resonance spectroscopy. As an alternative approach, high-resolution Kβ X-ray fluorescence spectra have been recorded on the dark-adapted S1 state and the hydroquinone-reduced state of the oxygen-evolving complex in photosystem II. By comparison of the Kβ chemical shifts with those of appropriate model compounds, the S1 state of photosystem II is found to contain equal amounts of Mn(III) and Mn(IV). In the hydroquinone-reduced sample, a significant fraction of the Mn is reduced to Mn(II). The results are compatible with models involving conversion of Mn(III)2Mn(IV)2 to Mn(II)2Mn(IV)2 clusters.

Influence of the core hole onKβemission following photoionization or orbital electron capture: A comparison using MnO and55Fe2Glatzel1, Bergmann2, Groot3 et al. 2001Phys. Rev. BSelf Cite521340View full textAdd to dashboardCite

“…The S term of the ground state under SO 3 symmetry transforms into A 1g in the octahedral symmetry O h of the cubic crystal field. If Dq/Bр2.8 where B is the Racah parameter ͓Bϭ(9 * F dd 2 Ϫ5 * F dd 4 )/441͔ the ground state configuration is t 2g 3 e g 2 with 6 A 1g symmetry as can be seen from the TanabeSugano diagram. 39 It has been found theoretically and experimentally that the crystal-field strength only has a minor effect on the spectral shape of the K␤ emission as long as a high-spin configuration in the valence shell is maintained.…”

“…In the case of photoionization, the core-hole-d-electron Coulomb attraction energy Q cd changes the relative ordering of the 1s3d 5 and 1s3d 6 L configurations in the intermediate and in the final state ͑Fig. 3͒.…”

“…The same scaling was then used for the PI and the KC calculations. For the calculation of the 1s intermediate states, the 1s3d 5 ⑀p and 1s3d 6 L⑀p channels were taken into account and no interaction of the continuum electron with the ionized atom was considered.…”

“…5͒, and metaloproteins like the 4-Mn cluster in the oxygen evolving complex of the transmembrane protein complex PSII. 6 In core-hole spectroscopy, the creation of a vacancy in an inner shell causes a considerable readjustment of the electrons. The ground-state Hamiltonian relaxes into the new Hamiltonian that includes the core hole.…”

“…[8][9][10][11] Taguchi et al calculated the 3p photoemission spectra ͑XPS͒, the K␤ fluorescence emission ͑XES͒, and the spin-dependent 1s absorption spectra of different Mn compounds by means of an MX 6 cluster model including three configurations. 12,13 They treated the K␤ emission as a coherent second-order optical process and emphasized the influence of the core-hole potential on the 1s excitation spectra.…”