Thomas Neisius

The first room-temperature X-ray absorption spectra of higher oxidation states of the tetra-manganese complex of photosystem II

The manganese (Mn) complex of photosystem II catalyzes water oxidation. For the first time, its advancement through the reaction cycle was monitored by time‐resolved X‐ray absorption measurements at the Mn K‐edge at room temperature. The complex was stepped through its four oxidation states by nano‐second‐laser flashes applied to samples exposed to the X‐ray beam. Time courses of the X‐ray fluorescence intensity were recorded during a flash sequence. Extended X‐ray absorption fine‐structure spectra were recorded with the S1, S2, and S3 oxidation states highly populated. The room temperature data is compatible with the formation of a third di‐μ‐oxo bridge between two Mn atoms upon the S2→S3 transition.

Characterization of the H2 sensing mechanism of Pd-promoted SnO2 by XAS in operando conditions

The effect of Pd nanoparticles on the H2 sensitivity of SnO2 thin films was studied in real working conditions using X-ray Absorption Spectroscopy (XAS), electrical conductivity measurements and mass-spectrometry.

Structural characterisation of solution species implicated in the palladium-catalysed Heck reaction by Pd K-edge X-ray absorption spectroscopy: palladium acetate as a catalyst precursor

Energy dispersive EXAFS (EDE), Quick EXAFS (QEXAFS), 13C NMR and X-ray crystallography have been used to probe the co-ordination sphere of palladium in the course of the phosphine free Heck reaction. [Pd2I6][NBu3H]2 has been isolated from the precatalytic solution and its crystal structure determined. EDE and QEXAFS spectra of the complexes Pd(OAc)2, Pd(PPh3)4 and [Pd2I6][NEt3H]2 illustrated the value of the technique in structure elucidation. EXAFS of the precatalytic solution detects [Pd2I6]2− and no co-ordinated carbon. EXAFS of the catalytic solution shows a first co-ordination sphere of 2 carbon atoms and a second of 2–2.5 iodines. A scheme involving an equilibrium between the oxidative addition product and the olefin co-ordination species, has been proposed to explain these results.

First steps towards time-resolved BioXAS at room temperature: state transitions of the manganese complex of oxygenic photosynthesis

Structural changes and redox transitions at the metal atoms of the active site are essential for the understanding of the catalytic mechanisms of biological metalloenzymes. First steps towards studying these processes by time-resolved X-ray absorption spectroscopy on protein samples (BioXAS) are reported. Photosystem II (PSII) catalyses the light-driven oxidation of bound water molecules at a tetranuclear manganese complex yielding the molecular oxygen of the atmosphere. In this work, first time-resolved XAS results under quasi-physiological conditions (at room temperature, non-crystalline samples) on PSII are presented. Perspectives of time-resolved BioXAS are discussed.

Extended X-ray absorption fine structure (EXAFS) characterisation of the hydroformylation of oct-1-ene by dilute Rh?PEt3 catalysts in supercritical carbon dioxideElectronic supplementary data (ESI) available: data includes the Rh K-edge EXAFS-derived structural/statistical parameters for spectra shown in Fig. 1. See http://www.rsc.org/suppdata/cc/b3/b311331k/

Dilute EXAFS characterisation has been used to elucidate species involved during the course of the 3 mM Rh-catalysed hydroformylation of oct-1-ene in scCO(2); significant metal clustering occurs with a Rh:P ratio of 1:1 but at a 1:3 ratio, metal clustering is not detected, with the presence of monomer species only.