A neutron-diffraction study of the low-cycle fatigue behaviour of an austenitic stainless steel 316

Abstract

SPring-8 in JAPAN.Since previous report has shown that the Mn 4 Ca-cluster suffer from serious X-ray radiation damage during data collection of PSII crystals [2], we adopted a slideoscillation method to collect the low-dose X-ray diffraction data using large PSII crystals (length: ~1mm), which allowed us to collect a full data set from nine irradiation points of one single crystal in a range of 180 degree.The X-ray dose irradiated onto each point was estimated to be half of the value determined by the spectroscopic method where the radiation damage begins to occur [2].In the crystal structure obtained at 1.9 Å resolution, the electron density distributions for each of the 5 metal ions were clearly separated, which were also confirmed by the anomalous difference Fourier map.Five oxygen atoms forming the oxo-bridges between the metal ions were clearly identified by the omitted Fourier map, and several water molecules were found to be associated with the metal cluster, which may function as substrates for the oxygen-evolving reaction.In addition, thousands of water molecules were found in the whole structure of PSII dimer.Some of the water molecules form a network linking the catalytic site and two chloride ion sites identified previously [3].Including protein subunits and co-factors, we will discuss the atomic resolution structure of PSII complex.