The investigation of water oxidation in photosynthesis has remained a central topic in biochemical research for the last few decades due to the importance of this catalytic process for technological applications. Significant progress has been made following the 2011 report of a high-resolution X-ray crystallographic structure resolving the site of catalysis, a protein-bound Mn4CaOx complex, which passes through ≥5 intermediate states in the water-splitting cycle. Spectroscopic techniques complemented by quantum chemical calculations aided in understanding the electronic structure of the cofactor in all (detectable) states of the enzymatic process. Together with isotope labeling, these techniques also revealed the binding of the two substrate water molecules to the cluster. These results are described in the context of recent progress using X-ray crystallography with free-electron lasers on these intermediates. The data are instrumental for developing a model for the biological water oxidation cycle.

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The structural flexibility … show that the core of the photosynthetic oxygen-evolving complex exists in two interconvertible structures with distinct spectroscopic properties. This solves the puzzle of the two interconvertible signals in the S 2 oxidation state of the catalyst, and paves the way for a deeper understanding of its function.

SUMMARYWe consider the hybrid output regulation problem for minimum phase linear systems with relative degree greater than one. In the hybrid output regulation problem, an exosystem provides a disturbance or tracking signal that must be matched via an internal model in order to asymptotically regulate the error. This hybrid exosystem is a linear system that experiences periodic jumps. In this context, we build upon previous works in hybrid output regulation by showing how high‐gain observers can successfully overcome the obstacle of high relative degree. In certain scenarios, they can also be used to stabilize the hybrid internal model dynamics through jumps. Copyright © 2013 John Wiley & Sons, Ltd.

Aus der Kristallstruktur des Photosystems II abgeleitete DFT‐Modelle zeigen, dass der Sauerstoff produzierende Komplex im S2‐Zustand in zwei Formen existiert, die energetisch ähnlich und ineinander umwandelbar sind. Damit wird eine seit langem offene Frage zur Spektroskopie dieses Zustands beantwortet: Eine Form ergibt das Multilinien‐EPR‐Signal bei g=2.0 (rechts im Bild; rot O, violett Mn, gelb Ca), die andere das g≥4.1‐Signal (links).